KEP Power Testing Blog

Post-Installation Cable Testing: Subcontracting or In-House Testing

noreply@blogger.com (Anonymous) — Mon, 05 Mar 2018 13:35:00 +0000

On a daily basis, power networks suffer from huge losses on account of cable system failure. In addition to undesired downtime caused by cables going out of order, substantial energy losses occur during electricity transmission due to the system malfunctioning. Yet, many of cable system failures can be prevented at the point of cable commissioning, provided proper post-installation cable testing is conducted.

Hiring a cable test contractor

One way to run post-installation cable testing is to hire an experienced professional contractor. When choosing one, it is advisable to take into consideration the following:

Reputation. Try to find out what other clients think of the contractor you are considering to hire. In the age of Internet, customer feedback can usually be found online, and it will be helpful to rule out contractors with a lot of dissatisfied clients or no reviews at all, which may be evidence of little experience.

Quote. Screening potential contractors, compare the quotes they offer for the job required. Beware of those quoting a price considerably lower than that quoted by the others, as cable testing requires qualification, experience, and a range of quality cable test equipment – remember, all these things are not cheap. Also, the quote should include the details of the job involved; this way you will not only be able to see how reasonable the price is, but also assess whether the contractor knows what they are doing.

Knowledge of applicable standards. You need to make sure that your contractor is capable to run post-installation testing while following the standards that apply to your cable system.

Running cable testing in-house

If your decision is to run cable testing in-house, you need to be aware of the following:

Test standards and results. Whether you’ve hired a contractor or going to run cable testing in-house, it is important to agree on the test standards you’ll need to adhere to and, accordingly, how you are going to evaluate the test results. Therefore, before testing begins, you should have a list of measurements to obtain with respective reference values depending on the applicable standards.

Staff training. A wide range of modern high voltage testing equipment allow for automatic effortless testing. However, this does not mean that you should neglect staff training. Quite the opposite, it is vital to invest in the education of the testing personnel, as this is essential for reliable test results and accurate interpretation.

The right cable testing equipment. Depending on your cable system, you may require a range of cable testing equipment. Prior to beginning the post-installation test, make sure you have instruments that will help to run cable proof testing (such as hipot testers) and, if cable failure is found, to prelocate the fault (usually with a TDR) and to conduct precise fault pinpointing (eg using a surge wave generator in conjunction with a surge wave locator ). Companies that do cable testing at large scales usually opt for cable test vans that integrate all the equipment required for cable testing.

Safe test area. High voltage cable testing should be conducted in accordance with best safety practice.

The equipment used during cable testing should have safety interlocks and/or other safety features.
Even if the test set being used has an automatic discharge function, use the discharge stick to ensure that the object under test has been completely discharged.
Make sure that only testing personnel are present at the testing site. You don’t need any bystanders there, whether public or company employees, as they are a potential hazard, first of all to themselves.

Summing up, whatever you choose, to subcontract post-installation testing or two run it in-house, this job requires extensive preparation, so you need to identify the scope of testing, what standards to follow, which tests to run and measurements to make for comprehensive assessment of the cable system being tested.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Integral Cable Test & Fault Locating Systems: Convenient Solution for Cable Commissioning and Maintenance

noreply@blogger.com (Anonymous) — Thu, 01 Feb 2018 07:19:00 +0000

Cable fault location presents a number of challenges, and how successful it is greatly depends on the nature of the fault, how remote the site is, and how skillful the repair crew are. Combined together, when the type of cable defect is unknown, testing needs to be done at a remote location, and the testing personnel have little experience in fault finding, these challenges might be difficult to tackle.

For this reason, KEP offers a series of cable test vans ETL, which provide the flexibility required for efficient fault finding.

A strong advantage of KEP’s cable test vans is that they comprise the most advanced fault locating equipment, offering DC hipot testing from 4 to 80 kV, with surge energy from 1000 to 2560 J.

The integrated hipot test set allows to run cable proof testing, while the time domain reflectometer ensures accurate fault pre-locating in the pulse echo (TDR), arc reflection (ARC), impulse current (ICE) and voltage decay (DECAY) modes.

The incorporated surge wave generator, used in conjunction with a surge wave locator, is responsible for acoustic fault pinpointing. Also, in the burn mode the surge generator is used for cable fault conditioning, which allows to pinpoint intermittent cable faults.

On the customer’s request, KEP delivers a test van supplied with all the required testing equipment. Alternatively, KEP can deliver the selected cable fault location system ETL for the customer to install themselves into a vehicle of their choice.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Cable Fault Location: Pinpointing Solid Shorts, Open Circuits & Splices

noreply@blogger.com (Anonymous) — Wed, 10 Jan 2018 08:07:00 +0000

SWG-12/1100R portable cable fault location system

A typical method of pinpointing a cable fault is arc reflection, which is performed with the help of a thumper (surge wave generator) and a time domain reflectometer (TDR).

This approach uses the gap at the place of a fault: a surge wave generator sends high voltage surges that, when bridging the gap, cause an arc to burn. This reduces the cable impedance at the place of the fault, creating a terminating event for the pulse of a time domain reflectometer.

As a result, the TDR pulse is reflected off the arc, and the TDR automatically measures the distance to the fault.

The limitation of this approach is that when the gap is too wide, the surge wave pulse cannot bridge it, and no arc can be created. The same is true for when there is no gap at all: if there is no gap, there is no air, and it is impossible to create an arc. Thus, in these two cases the TDR pulse will not find a terminating event and will not be able to pinpoint the fault.

Pinpointing a solid short (bolted fault)

A solid short, or a bolted fault, has not gap at the place of the fault. However, as it has zero impedance, the cable TDR trace will show a negative reflection at the place of the fault. All that needs to be done to localize this type of fault is measure the distance to this reflection.

Pinpointing open circuits

In contrast, an open circuit will be shown on the TDR trace as a positive reflection. To pinpoint this type of fault, the TDR identifies the distance to this positive reflection.

Receiver PT-14

Pinpointing a slice

Locating of a splice can be done using the impulse current mode of a time domain reflectomerter.

If the impulse current does not help, a splice can be pinpointed using a surge wave generator and a receiver (cable tracer). When a thumper transmits high voltage surges, the receiver will pick up a strong deflection at the place of a fault.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Season's greetings from the KEP Power Testing team!

noreply@blogger.com (Anonymous) — Fri, 15 Dec 2017 11:47:00 +0000

Breakdown Voltage Test of Transformer Oil

noreply@blogger.com (Anonymous) — Tue, 12 Dec 2017 11:00:00 +0000

Be it a transformer, a high voltage cable or a capacitor – any type of high voltage apparatus must be
maintained properly and timely. However, transformers are one of the most important elements of the power grid to be kept up-to-date as they are the main distributors of alternating current electrical energy. Both homes and businesses, actually, whole cities depend on their proper operation for stable energy supply.

Regular transformer oil testing is a crucial preventative measure that will help you keep your high voltage devices up and running. The dielectric liquid deteriorates over time due to moisture and impurities, losing its cooling and insulating properties. A common method for checking the oil quality is measuring its breakdown voltage.

Conducting the oil testing procedure periodically, you can keep the hydrocarbon fluids of the oil pure and keep its breakdown voltage high, which optimizes the overall transformer performance. Just take a sample of the dielectric liquid, fill it into the vessel of an oil dielectric tester (like one of the KEP OLT models), run a test, get the oil breakdown voltage and compare it with that set in one of the numerous standards.

KEP’s OLT oil dielectric testers provide an easy and reliable way to measure the breakdown voltage of dielectric liquids. These portable solutions allow to automatically run the whole testing process, which saves a lot of time and money.

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Cable Test Vans by KEP for Reliable, Easy and Efficient Cable Fault Location

noreply@blogger.com (Anonymous) — Thu, 09 Nov 2017 10:42:00 +0000

ETL-40 Vehicle Based System

Diagnostics of power cable sheath presents one of the biggest challenges in transmitting and distributing electricity, with the percentage of failure during cable exploitation still being high. These
failures happen due to the extremely long length of cable lines, soil inhomogeneity, and cable sheath heterogeneity along all cable length.

With the purpose of detecting serious insulation defects, megohmmeters are widely used. However, their readings cannot be relied on for the final evaluation of sheath condition because the readings depend mostly on the cable length and condition of bondings.

This is explained by the fact that the capacitance of power cables is high and, thus, is not fully charged in the time of resistance measurement. Therefore, the readings of a megohmmeter will not only be based on leakage current, but on charging current as well.

The most widespread method of monitoring the cable line sheath condition is testing with high direct current voltage. The aim of high voltage testing is to timely identify and fix degradation defects of cable sheath, couplings and bondings in order to prevent the appearance of cable faults during operation. So, the task of high voltage testing is to decrease quantity of cable failures while they are in being used.

The whole range of equipment required for diagnostics and high voltage testing is integrated in cable test vans by KEP.

Cable test vans by KEP allow to conduct high voltage testing of power cables and other elements of power grid systems such as insulators, power transformers winding, arresters, etc. The usage of such cable test vans makes cable fault location process much more efficient, easily tackling the issues that have been troublesome for power engineers for a long time.

Depending on the fault locating conditions, the distance to a cable fault can be measured with the incorporated RIF-9 using the TDR method, while the combination of surge wave generator and P-900 can be used to locate a fault with an acoustic method, and the combination of the LFG-generator and surge wave locator P-900 – with an inductive method.

In addition, the application of the time domain reflectometer RIF-9 makes burning at the place of fault unnecessary, which accelerates the process of fault location and elimination. As for the acoustic method, it has almost solved the issue of locating difficult-to-detect single-phase faults and fused cable faults.

Another advantage of cable test vans by KEP is that these can be mounted into any vehicle according to customers’ choice depending on specific application circumstances.

VLF-60 Very Low Frequency High Potential Tester

Also, KEP’s cable test vans can be customized to meet the customers’ requirements. For example, in order to test XPLE insulation cables, cable test vans by KEP can be equipped with a very low frequency high potential tester.

The main priority of applying high voltage test equipment is the safety of servicing personal. The experience which has been gained in the course of cable test system exploitation confirms that the cable test vans by KEP correspond to the industry’s electrical safety standards.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Cable Fault Location on Cross-bonded Cable Systems

noreply@blogger.com (Anonymous) — Mon, 02 Oct 2017 08:48:00 +0000

Cable systems of substantial length frequently apply cross-bonding as it allows to improve the current carrying capacity, and thus decrease power losses in the system. On the down side, this type of bonding presents a number of challenges to be tackled during cable fault location. This article describes a typical practice for testing cross-bonded systems.

What is cross-bonding

In cross-bonding, the circuit is made up of three (six, or nine) cross-connected minor sections, which form a major section. At the beginning of the first and at the end of the third minor section the shield is solidly grounded, with the second section isolated using shield ‘breaks”, and its sheath bonded to other phases. Due to such an arrangement, the total induced shield currents are reduced, which makes for an increased ability to carry useful current and higher safety to the cabling system.

Testing a cross-bonded cable system

The cable fault location procedure includes the following steps:

1. Learn about the cable system being tested, i.e. type of cable, insulation type, and total length of the circuit.

2. If needed, especially on new installations, run a sheath test to see if the integrity of the outer cable sheath is intact. For this test a test voltage is fed to the cable neutral. Current leakage resulting from the procedure indicates there is mechanical damage to the cable sheath.

VLF-60 Hipot

Note: In order to conduct this test on a cross-bonded system, the solid bonded link boxes need to be opened to remove the ground connections; any additional overvoltage protection devices should also be disconnected.

3. Run a preliminary VLF hipot test; this will make it possible to check the splices and terminations, to confirm a cable fault and identify the breakdown voltage.

4. Conduct cable fault pre-location (see below).

5. Pinpoint the fault with the acoustic method.

Cable fault pre-location on cross-bonded cable systems

One of the most popular approaches to fault pre-location is time domain reflectometry, which identifies cable events, like faults, splices, cable ends, based on the change in the characteristic impedance of the cable. In cross-bonded cable systems there are a large number of cross-bonding joints; predictably, the TDR signal is reflected off the first two or three joints and cannot go any further.

These influences can be eliminated by bridging the cross-connections with solid short-circuit jumpers that can be fixed directly.
If bringing cannot be applied, it is advisable to identify the cable section affected by the fault using a surge wave generator and a cable fault pinpointer.

Alternatively, while using TDR, attempt adjusting the pulse width and pulse voltage. In order to utilize this approach, it is important to understand that while a wider pulse width yields a stronger signal, the reflection at first-cross bonding points will be strong as well; at the same time, a too narrow pulse width means the signal will attenuate too fast. As for the pulse voltage, there is a direct connection between the amount of voltage applied and the quality of the TDR imprint: the higher the voltage pulse sent, the clearer the reflections in the longer cable sections.

Time Domain Reflectometer RIF-9

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Cable Fault Pinpointers: Choosing the Right Instrument

noreply@blogger.com (Anonymous) — Mon, 11 Sep 2017 06:14:00 +0000

Cable fault location cannot be imagined without the actual pinpointing of a cable fault, which can be challenging and time-consuming. How soon the result is delivered heavily depends on the pinpointer being used; yet, there still appears to be some confusion as to how to choose the right one. This article will highlight the differences between the principal pinpointer types, and, hopefully, will equip the users with the information needed to make the right choice.

Pinpointers with an acoustic sensor

Description: a basic type of pinpointers, which can be effectively used for fault pinpointing on short cable lengths provided the line route is known.

Advantage: low price.

Limitation: in most cases purely acoustic pinpointers are inefficient when it comes to locating a fault on unknown cable routes and/or longer cables as they cannot trace the cable route and measure the distance to the fault.

Pinpointers with an electromagnetic sensor

Description: an alternative to acoustic pinpointers, designed to pick the electromagnetic signal of the discharge.

Advantage: low price.

Limitation: also limited in applications since purely electromagnetic pinpointers are unable to measure the time delay between acoustic and electromagnetic signals, based on which the distance to the fault is identified.

Dual-signal pinpointers integrating one magnetic sensor

Description: fault pinpointing instruments equipped both with an acoustic and a magnetic sensor, making it possible to pick the two types of signal and calculate the respective time delay.

Advantage: the flexibility of switching between the acoustic and inductive fault locating methods makes such a pinpointer suitable for various testing conditions; can measure the time delay between acoustic and electromagnetic signals; significantly lower priced compared to the following type.

Limitation: cannot show the direction to the fault.

Dual-signal pinpointers integrating two magnetic sensors

Thus, out of the four described options, the latter two enable most accurate fault location in as little time as possible and, therefore, lower cable maintenance costs. The choice between them should be made based on your circumstances: the one with two inductive sensors will make the process faster, but at quite a high cost, whereas the reasonably-priced pinpointer with a single inductive sensor with an acoustic one is just as effective, being perfect value for money.

Dual-signal pinpointer incorporating an acoustic and electromagnetic sensor P-900

Pinpointer P-900 is designed to:

Locate underground cable lines and power cables;
Measure cable depth;
Pinpoint shorts;
Pinpoint insulation faults.

P-900 should be used with an auxiliary frequency generator of 1024 ± 2 Hz / 2048 ± 2 Hz and no less than 200 W of output power at the load range from 0.5 to 200 Ohms (e.g., LFG-2500) when searching using the inductive method.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Cable Test Vans from KEP for Fast and Accurate Cable Testing and Fault Location

noreply@blogger.com (Anonymous) — Thu, 17 Aug 2017 07:55:00 +0000

The progress in the power cable testing sector has equipped technicians with a range of high performance cable testing tools. Yet, despite the tendency for combining various testing techniques in one instrument, it is frequently the case that a complex of tools is required to tackle the job at hand. In these circumstances it is best to opt for a cable test van, like KEP’s ELT-Series test systems, which will ultimately help to save time and money, while facilitating effective fault location.

The ETL-Series cable test vans allow the user to carry out non-destructive diagnostics, testing and fault location on low and medium voltage power cables. These modular test systems comprise a thumper, a time domain reflectometer, and an audio frequency system, which gives the necessary flexibility in terms of choosing the most appropriate cable testing method. The fault location instruments integrated in the ETL test vans are from KEP’s product line and can be customized to the customer’s requirements.

The ETL-series test systems offer the most effective methods of power cable testing such as the acoustic thumping and TDR-based approaches. The latter include pulse echo (TDR), arc reflection (ARC), impulse current (ICE) and voltage decay (DCY).
Fault conditioning is achieved with the systems’ burning and arc reflection modes.

Fault pinpointing

One of the components of a KEP’s test van is the thumper, or a surge wave generator. In conjunction with the receiver P-900, it allows to effectively conduct acoustic cable fault pinpointing. Sheath faults can be pinpointed with either pulsed DC step-voltage or burning.

To facilitate cable route tracing and fault location, the test systems are equipped with an audio frequency generator.

ETL-8V Cable Test Van

Time domain reflectometry

Cable fault prelocation is achieved with the RIF-9 Time Domain Reflectometer, which can be operated either with the high contrast, high resolution touch-screen, or with the handy control knob. The RIF-9 can be used in the TDR mode; coupled with the system’s surge wave generator, it enables running tests in the modes of arc reflection, impulse current and decay.

The onboard memory stores test results and allows sending reports to a PC for further processing.

ETL-40V Cable Fault Location Test System

Audio frequency system

Utilizing the incorporated audio frequency generator (a 50 W LFG-50 or 200 W LFG-200), the ETL-Series test systems help solve the tasks of cable route tracing, fault location, depth measurement and cable identification. The LFG offers a choice of three frequency levels, 491 Hz, 982 Hz and 8440 Hz, and can be operated in a single or two-frequency modes. The load is adjusted automatically, with the overload trip interlock ensuring an even higher safety of operation.

In addition, the audio frequency system makes it possible to test a cable’s shield integrity and identify splices.

Safe operation

The ETL test systems comply with safety standards and integrate a system of interlocks, emergency stop, and key lock switch.

A vital component of the ETL safety is the earthing system delivered through operational, protective and auxiliary earth. To ensure proper operation, the ETL control unit monitors the voltage between protective and auxiliary earth as well as the resistance between operational and protective earth. The safety level is raised even further with the isolating transformer.

Also, the ETL systems incorporate overcurrent protection to make sure the object under test will not be damaged in case of the current exceeding the threshold value.

KEP’s ELT-Series

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

AC & DC Hipot Cable Testing with HVTS-HP from KEP

noreply@blogger.com (Anonymous) — Tue, 01 Aug 2017 06:32:00 +0000

HVTS-HP Control Unit

AC and DC hipot testing is widely utilized for diagnostics and testing of dielectric materials. As a large proportion of the world’s distribution network is approaching the end of its service life, the technicians regularly come across the need to conduct maintenance or acceptance tests. These measures frequently need to be taken on site, which means the industry’s demand for powerful compact hipot testers combining the two main types of hi potential testing is growing.

Understanding the challenges the utility sector faces, KEP offers the HVTS-HP Series High Voltage Test Systems intended for AC and DC high potential testing. These test systems are used for diagnostic and testing purposes, helping to prevent losses due to downtime. Using the HVTS-HP Series testers, the user can evaluate the condition of various low- to medium-capacitive components of cable networks.

HVTS-HP High Voltage Unit

Due to the friendly interface and intuitive manual controls, the test systems can be configured to suit the current testing needs. Also, the user can run tests automatically, which is especially useful for staff with less experience in withstand cable testing.

The HVTS-HP Test Systems maintain the output voltage at the user-specified level and generate a stable waveform while the output voltage is increased to the pre-set value. To achieve a high accuracy of test results, the systems measure the output voltage on the object being tested, thus providing the user with the relevant testing information.

The HVT-family testers ensure high safety levels, featuring current and voltage trip interlocks. Depending on the test requirements, the user can set the threshold output voltage as well as current and voltage trip values.

In addition, KEP provides a possibility to customize the HVTS-HP testers in order to help the customer reach specific testing objectives.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Cable Fault Location: Straightforward and Efficient

noreply@blogger.com (Anonymous) — Wed, 19 Jul 2017 08:07:00 +0000

Portable Cable Fault Location System SWG-12/1100R

The worldwide problem of the aging cable infrastructure brings about a greater than ever need for power cable maintenance testing and fault locating. Despite the common guidelines for cable fault location to be done by experienced professionals only, the circumstances frequently demand staff with insufficient fault locating skills to perform cable testing.

For this reason the industry has seen an increase in the demand for fault locating equipment flexibility, enabling both expert technicians and newbies to cable testing to efficiently diagnose cables and locate cable faults.

Suitable for testing of medium voltage cables up to 12 kV, KEP’s SWG-12/1100R portable cable fault location system keeps up with the industry’s requirements, providing cable testing simplicity, accuracy and safety to the user. The system combines a surge wave generator and a time domain reflectometer, which enables accurate diagnostics and precise pinpointing of cable faults.

Rather than having to choose between alternative cable testing techniques, with the SWG-12/1100R the user has the possibility to utilize the synergistic effect of the most popular fault locating techniques in a single cable test system. As the tester features both a surge wave generator and a time domain reflectometer (TDR), it helps to solve a range of objectives related to the cable testing process, including cable diagnostics, fault pre-location and pinpointing.

Thumper & TDR in a single tester

To make the process of cable fault location more straightforward for users with a lack of relevant skills, the cable test system features testing in the automatic mode. The intuitive control panel and user-friendly software further facilitate error-free testing. Also, the more experienced users can benefit from the manual mode, allowing to specify the test parameters and sequence.

The high levels of cable testing efficiency are achieved due to the powerful surge wave generator, which significantly speeds up testing of power cables, known for their high capacitance.

Easy test result interpretation with SWG-12/1100R

On account of the high voltage nature of power cable testing, a critical requirement to cable fault locating equipment is safety, both to the user and the equipment being tested. In the SWG-12/1100R the combination of a thumper and a TDR tester allows to bring down the cable load to the minimum, while safety checks prior to the beginning of testing prevent high voltage hazards caused by improper earth connections.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Cable Commissioning: Post-Installation Testing Tips

noreply@blogger.com (Anonymous) — Thu, 06 Jul 2017 08:44:00 +0000

The main purpose of post installation cable testing is to check the cable and accessories for any defects that may have occurred during the installation process. Should a defect be found, the techniques of after installation testing help pinpoint the place of the fault and repair it.

The steps to be performed during post installation testing depend on the requirements to the newly installed cable or cable system; they may include the insulation and conductor resistance tests, sheath and conductor phase identification, cross bonding test, sequence impedance measurements, serving tests to check the quality of the outer sheath, sheath or screen resistance tests, and HV tests.

This post is going to discuss what needs to be taken care of in the process of a cable system commissioning process. While being quite obvious, these steps are often ignored to speed up the test procedures, but failure to follow them is likely to result in injuries to the personnel and significant time loss due to resulting cable system downtime in future.

Safety comes first

Since power cable testing carries electrical hazard, it is crucial to ensure the safety of the staff involved and to prevent unauthorized access to the testing site. The people present at in the testing area are to be limited to the testing personnel, who should have an appropriate line of communication. The testing site should be fenced off and warning signs should be put up.

In addition to safety reasons, it is important to stay clear of potential interruption as, for instance, the undesirable actions of observers might compromise the testing results and lengthen the time of testing.

Abide by the industry standards and regulations

Codes for cabling installation and testing have been written for a reason and are a good source of safe, reasonable and efficient practice during cable system commissioning.

Discipline and experience to achieve accurate results

Cables under test should be properly deegenergized, with earthing applied before and after testing cable ends should be insulated and the necessary precautions should be taken to avoid accidental contact. Care should be taken to remove the semiconducting material of the oversheath so as to prevent a flashover while testing the sheath.

No short cuts should be taken, with sufficient amount of time allocated to remove all the cross bondings in the link boxes.

Have the right cable testing equipment at hand

To avoid any interruptions and delays in the testing process, it is important to have on site testing systems for cable diagnosis and fault location matching the tested cable system specification. The testing equipment should be properly calibrated and used by experienced personnel.

Having found a fault, double check

In case a defect has been found, it is necessary to discharge the cable and check the integrity of all cable connections. Following this, the testing procedure is repeated, and if the defect is confirmed, a time domain reflectometer (TDR) can be used for prelocation in conjunction with a fault pinpointing system to locate the exact place of the defect.

Discharge properly

The modern cable testing equipment is typically supplied with a discharge feature. However, a safe testing practice requires a manual discharge, so using a discharge rod at the end of the cable testing process should never be neglected.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

New Directions in the Solar Power Industry

noreply@blogger.com (Anonymous) — Fri, 23 Jun 2017 07:02:00 +0000

Solar balloons to generate renewable energy

A significant limitation of today’s solar installations is their unstable operation dependent on the amount of solar energy reaching the earth surface, varying based on the weather conditions, season and time of day.

The development of power plants utilizing solar balloons can become a new direction in renewable energy usage, which will enable a more efficient use of solar energy. The main element of such a power plant, a solar balloon, can be raised a few kilometers over the ground, floating above the clouds, and provide sustainable utilization of solar energy throughout the day.

In a stratosphere PV power plant, the two-layer PV surface of the installation absorbs solar energy, the thermal power of which causes the steam inside to heat. The light going through the outer transparent layer heats the interior layer; as a result, the steam inside heats to 100-150°С. The two layers are divided with gas or air serving as thermal insulation that reduces thermal loss to the atmosphere. The steam pressure is close to that of the air outside the stratosphere installation.

The water steam, through a flexible steam pipe, goes to the steam turbine and condenses in the condenser. The water is again supplied out of the condenser to the internal cavity of the sheath, where it evaporates due to contact with heated water steam. Such an installation can have an efficiency of up to 25%; in addition, using the water steam stored in the internal cavity, a stratosphere installation can operate at night. A 150-meter in diameter solar power balloon placed at an altitude of 5 km can have a capacity of 2 MW.

Stratosphere PV installation

1 – sheath of solar balloon
2 – thin-film solar cell
3 – string with a cable
4 – cable drum
5 – electric motor
7 – reductor
6 – inverter

Such a stratosphere PV power station can be placed hundreds of meters above the ground with a steam-turbine unit on the ground, or above the sea surface with the power unit located on anchored platforms fixing the stratosphere installation. The operation of a 5-7 km high stratosphere power plant does not depend on weather conditions, and the steam turbine unit can be placed either on the ground or in the basket of the solar balloon. In the latter case electricity is transmitted to the ground along a cable. Currently, such solar balloons are used in Taiwan.

The first experimental solar PV power plant, launched in 2003, consists of a solar energy receiver made up of several layers of flexible spherical sheaths. An important benefit of the installation is the fact that the steam condensed by the condenser into the separated compartments of the space between the transparent and absorbing layers circulates on the lit side only. This 2 MW stratosphere PV installation occupies an area of 0.3 km2. In another solar installation, launched in 2005, the centre of the 300 m in diameter sheath is at an altitude of 450 m, which made it possible to substantially reduce the occupied area. Having a positive experience of exploiting such stratosphere PV stations, Taiwan intends to use them on a wider scale.

Space-based solar power plants

Another important direction in the development of solar energy exploitation is the creation of orbital solar power plants with solar arrays accumulating the energy of the Sun and converting it into microwave or laser emission directed at the Earth, where it is received with designated antennas and then converted to electrical energy.

For the purpose of converting solar energy into electricity, the industry uses solar cells, which, combined together, make up solar arrays.

In space, where there is no atmosphere, clouds, the change of day to night, the amount of solar energy is ten times as much as that on the ground. Research into the development of orbital solar power stations began in 1970s in the USA, USSR and other countries.

Currently, orbital solar power stations are being developed in the USA, Russia, Japan and other countries. This work utilizes the latest technological developments in photovoltaics, electronics, and robotics. More research is required on the ways to reduce the weight and cost of orbital power stations.

Around 2030, Japan intends to assemble an orbital solar power station at an altitude of 36 thousand kilometers, which is to transmit electricity to earth as a microwave beam, to be received by an Earth station antenna. The Japanese scientists have developed solar cells converting solar radiation into a laser beam with an efficiency of 42 %.

Source (Russian language): http://energetika.in.ua

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Photoelectric Conversion of Solar Energy

noreply@blogger.com (Anonymous) — Thu, 15 Jun 2017 05:53:00 +0000

Basic Principle of Photovoltaics

Molten Salt Power Tower

Photovoltaics is to do with the direct conversion of solar radiation into electricity. A photoelectric converter uses the photoelectric effect typical of certain materials. This effect is exhibited when photons of light fall onto a material and electrons are emitted as a result, generating photoelectric current.

To put it simply, when falling onto a solar cell made of two materials with different electric conductivity (N-type and P-type), the photon dislodges an electron, creating a free electron and a hole. As a result, the balance of the so-called PN junction is distorted, which causes electric current to flow.

A photovoltaic cell’s spectral response depends on the wavelengths of the falling light and thinness of the cell top layer. In clear weather a silicon solar cell generates electric current of about 25 mA at a voltage of 0.5 V per 1 cm2 of the cell area, that is, 12-13 mW/cm2. The theoretical efficiency of silicon solar cells is about 28%, and practical efficiency – 14 to 20%.

Silicon solar cell diagram

When series-parallel connected, solar cells make up a solar (photovoltaic) array. The capacity of solar arrays produced in the industry is 50 to 200 W. In photovoltaic power plants solar modules are used to build photoelectric generators. The service life of such a power station is 20 to 30 years, at low operating costs.

The drawbacks to using flat photocells to produce electrical energy are their high cost (up to 5 USD/W) and large areas required for setting up of photo power plants.

Solar power plant chart

Concentrator photovoltaics

One of the important developments in the field of photovoltaics is the advancement of concentrator photovoltaic installations. The system of solar energy concentration consists of a concentrator and a solar tracker because CPV units pick up only direct solar radiation.

Nowadays the basis for production of low concentration CPV modules is silicon. For instance, Australia produces crystalline silicon modules with a concentration of 11 suns and efficiency of 21.6%, while the USA manufactures silicon modules with a concentration of 40 suns and efficiency of 20%.

To improve the efficiency of solar energy conversion, gallium arsenide is applied, the high-temperature photovoltaic loss of which is much lower than that of silicon.

With the use of gallium arsenide there have been created two- and three-junction modules with a high efficiency at a concentration of 1000 suns and more. There have been created laboratory samples of CPV cells with an area of 0.5 cm2, a concentration of 500 suns and efficiency of 40%.

Specialists in the field of photovoltaics predict that the most promising CPV modules are going to be the ones with a concentration of 1000 suns, operating with the next-generation multi-junction gallium arsenide solar elements.

Applications of Solar Cells

One of the examples of using solar cells is photoelectric transport, with many companies creating vehicles powered by solar cells. The first solar plane was made in 1980; its flying distance was 160 km. In 2015 Solar Impulse 2 became the first solar plane to make a round-the-world trip, having spent 23 days without landing.

Some research has also been done in the development of solar powered car; the first automobile powered by a solar array was built in 1977. Currently, auto manufacturers are developing solar roof options to power their cars.

In addition, photovoltaics plays an important role in powering satellites and telescopes, helping achieve a significant economy of fuel consumption.

Source (Russian language): http://energetika.in.ua

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Types and Design of Solar Power Plants. Solar Power Industry

noreply@blogger.com (Anonymous) — Wed, 07 Jun 2017 08:21:00 +0000

There are two primary ways to convert sunlight into electrical energy: thermodynamic and photovoltaic methods. The thermodynamic approach utilizes the conventional approach of converting solar energy into electricity in thermal power stations, where the heat released by burning fuel is replaced with concentrated solar power.

Long parabolic (in their cross-section) heliostats with tubes for heating the transfer medium

Depending on their structural features, solar thermal power stations can be categorized into three main types:

solar power towers with a central receiver steam generator concentrating the solar light reflected by heliostats;
parabolic troughs, where along the focal lines of parabolic collectors there are tube receivers with a heat transfer fluid;
dish systems, which are made up of a parabolic reflector and a receiver located at the reflector’s focal point.

Solar Power Towers

Solar power towers contain five basic elements: an optical system, a control system for heliostats and the station as a whole, a steam generator, a tower supporting a solar collector, and a system responsible for energy conversion. The latter is made up of heat exchangers, energy accumulators, and a power conversion unit.

Solar power tower diagram

Since such a power station uses direct sunlight, concentrating solar systems continuously track solar activity, with each heliostat operating independently of each other.

The temperature achieved atop a tower with the help of concentrating elements is 300 to 1500°С. A single module provides a capacity of up to 200 MW, which is explained by losses during energy transfer from the furthermost concentrators to the top of the tower.

Solar thermal power plant “Solar Two”

The global experience in utilizing solar towers has proved the feasibility and effectiveness of these projects. Some of the main disadvantages of such power stations are their high cost and the large area they occupy. For instance, a 100 MW solar power tower occupies an area of 200 hectares.

One of the first large-scale solar-thermal projects, the power station “Solar Two” was in operation from 1981 to 1999 in the Mojave Desert (California, USA); its output was over 10 MW. The power station’s solar tower was surrounded with 1926 heliostats, a total area of 83000 m 2. It is interesting to note that the sunlight heated not water, but a heat transfer medium made up of sodium and potassium nitrates. In its turn, the medium caused the water producing steam for the turbines to boil. In 1999 the station was rebuilt into a huge Cherenkov telescope with the purpose of studying the effect of gamma rays on the atmosphere.

Solar power plant in Seville (PS1), Spain

The light reflected from large mirrors is so bright that it illuminates the particles of dust and moisture in the air; due to this we can see the beams surrounding the stunning white tower.

A more recent solar tower project was launched on March 30th, 2007 in Sanlucar la mayor near Seville, Spain. A beautiful concrete tower 115 m high and 624 heliostats, an area of 120 m 2 each, supply steam to the power conversion unit with a capacity of 11 MW. This is enough to provide electricity to 5000 houses, saving 18000 tons of carbon emissions per year.

A similar station, but with a higher capacity of 20 MW, was later added to this solar power station. The larger tower is surrounded with 1255 heliostats; its launch reduced carbon emissions to the atmosphere by 54000 tons a year and gave electricity to 18000 houses. The total capacity of this solar power plant is 300 MW, which is enough to meet the electricity demands of a city the size of Seville.

Parabolic Troughs

Parabolic troughs use parabolic reflectors, which concentrate beams of sunlight on the receiver tubes located at the focal point of the structure and contain liquid heat transfer medium. The medium heats u[ to about 400°С and goes through a series of heat exchangers. The resulting steam powers a typical turbine generator, which task is to generate electrical energy.

Parabolic trough diagram

Parabolic troughs are used throughout the world; their popularity being due to a simple system ensuring tracking of the Sun’s position and higher cost-efficiency compared to the other types of solar power plants. The cost of parabolic troughs is close to the cost of nuclear power stations.

Dish Systems

Dish-type power stations use parabolic dishes, which concentrate solar energy on the receiver located at the focal point of each dish.

Dish system

The working liquid in the receiver heats up to 1000°С and its energy is used for generating electricity either in a Stirling engine or in a Brayton cycle engine unit. Such installations also have systems that track the Sun. The maximum diameter of the dish is 20 m, which ensures a capacity of 60-75 kW. The cost of a dish-type power station can be lower than that of tower or parabolic designs.

Dish system

The solar power station of the company Solucar in Sanlucar la mayor tests various innovative technologies. For example, it combines parabolic concentrators with Stirling engines and extra-long parabolic (in their cross-section) reflectors with tubes for heating the heat transfer medium.

Naturally, solar power stations are more efficient in regions with a high level of sun radiation and low nebulosity. Their efficiency ratio can reach up to 20%, and capacity - 100 MW.

The next article is going to discuss photoelectric conversion of solar radiation.

Source (Russian language): http://energetika.in.ua

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Preventive Transformer Oil Testing

noreply@blogger.com (Anonymous) — Tue, 16 May 2017 08:49:00 +0000

Transformer Explosion Breaking News

Transformers are among the most expensive assets in the power network, representing over half of substation capital cost. In that extremely valuable transformer the cellulose insulation is the one component that will degrade with age and cannot be replaced without considerable cost and loss of service. Of the factors that can degrade the cellulose insulation – moisture, temperature, and oxygen – moisture is the most aggressive combatant.

Excessive moisture and other impurities in the paper and oil can significantly reduce the dielectric strength and the partial discharge inception levels; therefore, it has a profound effect on the aging rate.

Transformer Insulation Paper

To put it simply, moisture and contamination in the transformer’s insulation system cause the molecular chains of the cellulose to decompose, in turn accelerating the aging process of the cellulose
and adversely affecting the tensile strength and dielectric properties of the insulation. The result can be catastrophic, ending in premature failure, with replacement involving a considerable amount of time and expense – vital assets that you cannot afford to waste.

Yet, power utilities across the globe are faced with reductions of capital spending, retirement of experienced personnel, and crippled maintenance budgets. Existing resources must be leveraged to get the most out of assets that are nearing the end of their useful life.

Meeting the growing demands of the grid, while maintaining system reliability with this aging fleet is extremely taxing and uneconomical. Without significant changes in the way the utility operates and cares for its transformers, resources will be lost at exponential rates, but traditional maintenance is reactive rather than proactive.

Transformer Oil Testing

For these reasons, regular transformer oil testing saves real time and money to reduce maintenance, and defers the need for capital expenditures to replace these critical expensive assets in the long term. With this no-risk and cost-efficient procedure you can protect a million-dollar investment and ensure that your power transformers perform to their full potential.

OLT Testers by KEP

The OLT Insulating liquid testers by KEP are designed for measuring the oil dielectric breakdown voltage; the A-Series oil testers are fully automatic, produce accurate testing results, safe for the operator, and comply with the industry’s main standards.

The OLT insulating liquid test sets switch off the voltage feed to the electrodes immediately after the testing is over, which allows for testing dielectric liquids susceptible to disintegration due to arcing caused by a breakdown.

Main features of the KEP oil testers OLT A-Series:

Oil Test Set OLT-100A

Fully automatic operation
Fully compatible with IEC 60156
Preset testing programs for different standards
Built-in printer
PC connectivity
Internal test data storage
Precise direct voltage measurement
True sine high-voltage on electrodes
Oil temperature measurement

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Non-Conventional Sources of Energy. General Information

noreply@blogger.com (Anonymous) — Fri, 28 Apr 2017 06:40:00 +0000

One of the major development directions in the energy sector is the widespread usage of renewable energy technologies. The keen interest in alternative energy resources is mainly due to the fact that they are environmentally-friendly and thus make it possible to reduce the negative environmental impact of the energy industry, increasing the levels of energy and ecological safety.

Renewable versus Non-Renewable Energy Sources

The conventional sources of energy are represented by non-renewable resources such as coal, natural gas, oil and uranium; while renewable sources include hydropower and fuel wood.

The modern energy industry is mainly dependent on non-renewable energy resources, which are limited and cannot guarantee the sustainable development of the world’s energy sector in the long term period. Another substantial drawback of using non-renewables is their devastating effect on the environment.

In contrast, the non-conventional or alternative energy relies on solar power, wind power, geothermal energy, biomass, hydro power, which are potentially infinite in the foreseeable future. All renewables can be divided into two groups: those using direct solar power and those reliant on its secondary manifestations (indirect solar power) as well as the energy of interaction between the Sun, Moon, and Earth.

The indirect activity of the Sun results in respective effects in the atmosphere, hydrosphere and geosphere, mainly in wind power, hydro power, the energy of waves, tidal energy, geothermal energy, etc. Also, the non-conventional renewable energy includes small hydropower with hydro power plants, the capacity of which is up to 30 MW, or even up to 10 MW in some countries.

Compared to conventional unsustainable sources, the main benefits of renewables are that they are next to infinite and diminish the negative effects on the environment, such as the greenhouse effect, radioactive and thermal pollution, etc.

Types of Renewable Energy

Rising Energy Demands to Shape the Future Energy Systems
The main factors limiting the usage of non-conventional renewables are the following:

the low density of the power flow, which, for instance, is 1.36·10-3 MW/m2 for solar energy on the Earth surface, wind power at a wind speed of 10 m/s – 6·10-4 MW/m2, geothermal – 3·10-8 mW/m2, whereas for the nuclear power it is 0.2 MW/m2;
the uneven generation and consumption of energy;
the relatively high cost of generating units and of energy generation.

At the same time, the need to use alternative sources is defined by the fast growth of energy demand, which, compared to the year 2000, is expected to increase by two by the year 2030, and by 4 by the year 2050; the prospective depletion of the known natural fuel resources; the critical condition of the environment due to it being polluted with nitrogen and sulfur oxides, carbon dioxide, dust-like particles caused by fuel combustion, radioactive and thermal pollution, etc.

Renewable energy resources have some conceptual differences, so the ability to use them efficiently is based on the scientifically developed principles of converting renewable energy into the type of energy required by consumers. The environment always has the flows of renewable energy, so in the process of alternative energy development it is crucial to take advantage of local energy resources, while selecting those most efficient.

The use of renewable resources should be multivariable and complex, which will facilitate a particular region’s economic development. For instance, alternative energy resources can be found in agro-industrial systems, where animal and garden waste is used for obtaining biogas, liquid and solid fuel, and for producing fertilizers.

The effective planning of renewable-based energy systems involves the following:

regular research of the environment similar to geological exploration done when searching for oil or gas;
studying the region’s energy demands in industrial manufacturing, agricultural production and household requirements. To put it in other words, to select the most economical source of energy, it is important to know the structure of energy consumers.

Potential of Renewable Energy

One of the main characteristics of renewable energy sources is their energy potential. This parameter represents the amount of energy typical of the respective renewable resource. For evaluation purposes the renewable energy sources are differentiated as having the following energy potential:

theoretical, defined as the total amount of energy;
technical, defined as part of the theoretical potential, which can be utilized with the contemporary equipment;
economic, defined as the part of energy potential, which is reasonable to use considering economic, social, ecologic and other factors.

The approximate data on the world’s renewable energy sources are shown in the table below.

Energy potential of renewable energy sources

Renewable energy resources	Potential, billion tons of oil equivalent / year
Renewable energy resources	Technical	Economic
Direct solar power	5	1
Thermal energy of seas and oceans	1	0.1
Wind power	5	1
Hydro power, including:
- energy of currents	4.5	2.6
- energy of waves	0.05	0.01
- tidal energy	0.7	–
Biomass power (excluding wood fuel)	2.55	2.0
Geothermal energy	0.4	0.2

Source (Russian language): http://energetika.in.ua

About KEP

KEP (KharkovEnergoPribor Ltd.) produces high voltage testing equipment, including portable testing instruments and cable test vans, for the world’s leading power engineering companies. The KEP’s product range includes solutions for cable tracing, cable diagnostics and fault locating, testing high voltage instruments and safety gear, and oil dielectric testing.

We at KEP believe that our main task is to translate the customer’s requirements into the top-quality product, combining cutting-edge technology with fundamental high voltage testing principles.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

KEP Power Testing (KEP) at The Exhibition ElcomUkraine 2017

noreply@blogger.com (Anonymous) — Tue, 18 Apr 2017 11:26:00 +0000

Last week KEP Power Testing (KEP) took part in the exhibition elcomUkraine 2017, which displayed equipment for the power engineering industry. The event was held in the Ukrainian exhibition centre “KyivExpoPlaza”, presenting manufacturers from Ukraine, Turkey, China, Austria, Belarus, South Korea, Poland, Germany, Slovakia, Sweden, and Lithuania. The visitors to the exhibition included companies from Ukraine, CIS counties and other regions of the world.

KEP Power Testing presented well-established high voltage testing instruments along with its newest developments that are not yet produced in the CIS countries. The KEP products were displayed as equipment samples; the visitors to the KEP’s stand were able to use some of the product samples for actual testing, study the menu, select the required operating mode and simulate a particular job.

Among the professionals visiting our stand there were those currently using KEP instruments in their jobs, working in our cable test vans, applying insulating oil testers, test sets for cable fault location and other instruments for testing high voltage equipment.

A great benefit of such events is the ability for businesses to network and promote the industry’s latest advancements in the local market and globally. Over the course of these three days KEP gained over a hundred new prospective clients, who expressed their intention to cooperate with our company.

Also, the KEP team believes that business exhibitions of this kind are an amazing opportunity to track the changes in the industry’s consumer demand and obtain the information needed to forecast the future developments in the customers’ needs and the power engineering sector as a whole.

About KEP

KEP (KharkovEnergoPribor Ltd.) produces high voltage testing equipment, including portable testing instruments and cable test vans, for the world’s leading power engineering companies. The KEP’s product range includes solutions for cable tracing, cable diagnostics and fault locating, testing high voltage instruments and safety gear, and oil dielectric testing.

We at KEP believe that our main task is to translate the customer’s requirements into the top-quality product, combining cutting-edge technology with fundamental high voltage testing principles.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Perspectives on The Development of Non-Conventional Renewable Energy

noreply@blogger.com (Anonymous) — Fri, 07 Apr 2017 19:04:00 +0000

Due to the world’s energy crisis in the end of the twentieth century, the power sector began studying the potential of renewable energy sources.

Renewable sources of energy are now used in both developed and emerging economies. Major advancements in the renewable energy sector have been made where it has been strongly supported by the government on the financial and legislative level, with an emphasis on funding the development of the renewable energy technology.

In the beginning of the twenty first century the share of all renewable energy sources (including conventional hydropower and wood) in the gross energy consumption made up 14%, and in electricity consumption – 19%.

A substantial increase in the utilization of non-conventional renewable sources, especially since the turn of the twentieth century, has been typical for most developed and many developing economies. For instance, in 2006 in the EU countries the share of electric energy produced from non-conventional renewable sources came to 12,1% in Denmark, 13,1% in Finland, 4% in Hungary, 2,8% in Greece, 2,8% in Italy, 2,8% in Spain, 14,2% in Germany, a total of 87.6 billion kW·h, including small hydroelectric stations – 20.7 billion kW·h, wind power stations – 39.5, thermal power stations using biomass and biogas – 23.8, solar panels – 3.5, and geothermal – 0.1.

The positive experience of the EU countries indicates that among the many factors affecting the scale and future of utilizing renewable energy sources, the most important consideration is the government financial support of the country. One of the main directions of the Kyoto protocol on reducing greenhouse gas emissions is large-scale deployment of green energy sources.

The Future of Renewable Energy

In 2010 in the EU countries the share of renewable energy (including conventional hydro power stations) comprised 22 per cent, a large proportion of which coming from non-conventional sources; and by the year 2020 the European Union is expected to raise its energy consumption from non-conventional sources to 20 per cent.

If this project comes to life, it is going to be the largest in the world. The electric energy will be transmitted to Europe via a cable that is to be installed in the Mediterranean Sea.

Solar Power Station in Sahara

The projected use of non-conventional renewable energy sources in 2020

Energy source	Minimum scenario		Maximum scenario
Energy source	mln tonne of oil equivalent	share in gross renewable energy, %	mln tonne of oil equivalent	share in gross renewable energy, %
Biomass	243	45	561	42
Solar power	109	20	355	26
Wind power	85	16	215	16
Geothermal power	40	7	91	7
Small hydropower	48	9	69	5
Ocean power	14	3	54	4
Total	539	100	1345	100
Share of gross world’s demand in primary energy sources, %		3–4		8–12

In Japan the contribution of non-conventional renewables to the electricity production was 1.2% in 2000, 3% in 2010, with a target of 10% for the year 2030.

By 2020 Russia plans to increase its share of non-conventional renewable sources to 4.5%, and China – to 16%.

Some of the Reasons for Developing Renewable Energy

In many countries, especially in those dependent on the import of conventional energy sources, a strong motivation for the development of renewable energy is ensuring secure energy supply.

The cost of many technologies related to utilizing renewables and that of the energy generation is steadily decreasing due to the advancements made in the sector and economy of scale.

Non-conventional renewables are becoming more and more competitive in such areas of the energy industry as electricity generation, heat supply, and autonomous energy supply systems.

By the middle of the twentieth century non-conventional renewables may become one of the most important energy resources. Their contribution to the energy balance of many countries might come to 40–50%.

Combining Conventional and Non-conventional Energy Sources

Since many alternative energy sources are unstable in terms of their energy potential (caused by changes in wind speed, solar intensity, river flow, etc.), they are used in energy combination systems along with conventional energy sources. In addition to these, in local heat and electricity supply systems renewables are used in conjunction with various types of thermal and electric energy storage as well as hydrogen-based storages. This increases the efficiency of renewable energy sources and allows for stable energy supply to consumers. In the future, alternative energy source may become a primary source of water-based hydrogen production.

Source (Russian language): http://energetika.in.ua

About KEP

We at KEP believe that our main task is to translate the customer’s requirements into the top-quality product, combining cutting-edge technology with fundamental high voltage testing principles.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

Basic Information on Circuit Breaker Maintenance

noreply@blogger.com (Anonymous) — Fri, 24 Mar 2017 13:28:00 +0000

Circuit Breaker Tester

Billions of circuit breakers are installed in residential and non-residential buildings, or are used for industrial applications. These automatic electrical switches make it possible to switch currents on and off during the normal operation of the grid, and to automatically switch the current off if it exceeds the permissible value for a certain period of time.

In order to allow for typical appliance-inrush-currents, the circuit breaker must remain stable during a minor short-term overload. However, if the overload persists, the circuit breaker must open the circuit after a certain period of time. During a short-circuit, a circuit breaker must interrupt the current safely in order to minimize damage.

Design and operating principles of a circuit breaker

A circuit breaker has a rather sophisticated design, consisting of two separate tripping mechanisms for overloads and short circuits. Circuit breaker tripping characteristics show a thermal trigger for overloads, and a magnetic trigger for short-circuits.

Inside of a circuit breaker, the path the current is taking across the closed contacts is visible, as are the tripping components. The higher the amplitude of the overcurrent, the faster a circuit breaker must trip.

This is achieved with a metallic element consisting of two different metals which are heated up by the current flow. The two metals are expanding at different rates while they are heating up. An overcurrent that is present long enough will eventually activate the breaking element. This mechanism is tripped when the current exceeds its rated value by a relatively low figure of 1.45 – 2 times. At the same time, the tripping time, which depends on the current value (the higher the current, the faster the heating time for the metallic element), can reach up to 2 hours.

A circuit breaker must open a circuit instantaneously when it encounters a short circuit at several times the nominal current. A solenoid and a piston are the elements used for instantaneous tripping. A short circuit creates an instant magnetic field that moves the piston and operates the breaker.

Another important point is that interrupting high fault currents can result in heavy arcing. Due to magnetic forces, the arc moves through a stack of metal plates, where it is cooled, split, and finally extinguished at the next zero crossing.

Testing circuit breakers

The quality of the materials used by the manufacturers differ widely.
Therefore, it is a good idea for users to test their circuit breakers and not simply rely on them.

During testing, the circuit breaker is disconnected from the circuit and connected to a primary injection test set, which, in essence, generates different currents in order to simulate load conditions and fault currents.

Circuit Breaker Tester UPA-16

In thermal-magnetic circuit breakers both the electromagnetic and thermal tripping elements need to be tested. The testing current is selected based on the technical parameters of the given circuit breaker provided in the respective documentation. These parameters stipulate at what current load and in what time the circuit breaker should trip.

As for the testing sequence, the short circuit tripping element is tested first. Then, the overload tripping element is tested, followed with a stability test with nominal current.
If either of the tripping elements fails to trip the circuit breaker in the set amount of time, the circuit breaker under test is considered to be out of order and must not be operated any longer.

Circuit breaker testers UPA-series by KEP

Circuit breaker testers UPA are intended for automatic testing of circuit breakers with alternating current. The devices allow measuring the values of the supplied current and timing the circuit breaker tripping time. The UPA operates on the principle of varying the power in the primary circuit of the matching power transformer and, respectively, varying the output current flowing through the circuit breaker under test.
Power adjustment can be done either through an external voltage source or through a built-in thyristor controller.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Role of Interconnections in Long-Distance Energy Transmission

noreply@blogger.com (Anonymous) — Tue, 14 Mar 2017 07:10:00 +0000

The first steps made in the field of connecting local power grids showed that the interconnections between power systems should have sufficient transmission capacity and be able to distribute electrical energy over distances of hundreds of kilometers.

The crucial issues related to long distance energy transmission were addressed at the beginning of the twentieth century. By this time two main directions in electrical energy distribution had been developed – through overhead transmission lines and underground cable lines. Further advancements in both these directions revealed that overhead lines and cable lines are different in terms of the possible applications due to their respective structural features.

When it comes to overhead transmission lines, atmospheric air serves as the main dielectric medium insulating wires from the ground, surface structures, and from the other phase wires between supports. This makes it possible to relatively easily raise the transmission line voltage and capacity by increasing electrically safe distances between wires and the ground or other objects such as buildings (the wire insulation grade should simultaneously go up). At the same time, longer distances between wires and the ground lead to utilizing a larger territory and above-ground space for installing overhead lines.

Cable lines are made of current conductors, the whole length of which is covered with insulating and protective sheaths, and the thickness of which is a few times less than the safety margin of overhead lines. The thin insulation of cable lines allows for efficient space usage during line installation. However, until the end of the twentieth century there was no technology available for laying long-distance cable lines with voltage over 40 kV; thus, the transmission capacity was limited. Another thing to bear in mind is that large electrical capacity of AC cable lines with a voltage of 110 kV and higher considerably limits their length to a few dozens of kilometers due to overvoltage occurring during operation.

AC cable lines are typically used as a local means of distributing electricity among consumption points when the construction of overhead lines is deemed impractical. Cable lines are made into electricity distribution systems in cities and other residential areas, manufacturing enterprises and housing. The usage of cable lines for interconnections has only been practical in the context of high-voltage power direct current, which removes the limits on the length of interconnections. DC cable lines have been utilized for asynchronous connection of power supply systems divided by large water bodies, e.g. the English Channel, the Baltic Sea, the Adriatic Sea, and the Tyrrhenian Sea.

Overhead transmission lines are the most widespread since their installation cost, related to their transmission capacity, is much lower than that of cable lines; in addition, overhead lines are easier to install and maintain. Summing up, the fact that overhead lines are the ones used for interconnections is explained by their ability to transmit electricity over long distances with high transmission capacity.

Source (Russian language): http://energetika.in.ua

About KEP

KEP (KharkovEnergoPribor Ltd.) produces high voltage testing equipment, including portable testing instruments and cable test vans, for the world’s leading power engineering companies. The KEP’s product range includes solutions for cable tracing, cable diagnostics and fault locating, testing high voltage instruments and safety gear, and oil dielectric testing.

We at KEP believe that our main task is to translate the customer’s requirements into the top-quality product, combining cutting-edge technology with fundamental high voltage testing principles.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

The Development of Transnational and Transcontinental Synchronous Power Grids

noreply@blogger.com (Anonymous) — Thu, 02 Mar 2017 11:37:00 +0000

At the end of the twentieth century in the world’s energy sector there was a clear trend for the integrated power systems to merge into wide area synchronous grids, both nationally and internationally. These synchronous electrical grids supplied energy to territories as big as the habitable land on the continents, and the numerous power suppliers contributing to the integrated power grids created a competitive international power supply market.

At that time in North America, Europe and Asia there were 7 high-capacity synchronous electrical grids that integrated power systems on vast territories with a population of over a billion people (see Table 1 for the details on these power grids).

Economy of Scale as a Stimulus to Interconnections

The development of wide area synchronous grids was driven by economic considerations, as large power systems enabled the utility sector to provide higher quality electrical energy at a lower price. Wide area synchronous grids are typically made of integrated power grids or parts of national energy systems with their areas of operating control (system operators).

These components are combined into a single synchronous area with high-capacity interconnections, first of all enabling to exchange electrical energy produced at the points where primary energy resources are obtained (water resources, biofuel) or generated at a nuclear power plant. Through the coordinated control of the integrated power grid development and operation, the utility sector has the ability to efficiently utilize primary energy sources, decrease energy loss during transmission, efficiently use reserve capacity, and generate electricity at the lowest reasonable cost.

When perturbations occur, the coordinated operation of the energy system components ensures mutual assistance and gives the possibility to speedily resume electricity supply after a system failure. Also, the competition of energy producers in the international power market promotes a lower electricity supply cost.

Table 1. Parameters of the largest energy systems

Location	Area, thousand square km	Yearly energy output, TW·h	Maximum load, GW	Installed capacity of power stations, GW
Eastern USA and Eastern Canada	5154	2950	508	722
Western USA, Western Canada and Mexico	3108	874	112	158
Russia	5100	791	127	192.6
Western and Central Europe	2818	1558	251	414.2
Northern Europe	1228	366.7	55	88.7
Western Japan	173	556	78	97.8
Eastern Japan	119	408	58	67.7

Basic Rules of Interconnected Operation within Integrated Power Grids

Balance between electricity demand and consumption

Behind the joint synchronous operation of the power grids that are part of transnational integrated power supply systems found in Europe and North America is the understanding that energy systems are interdependent, collaborate on the technical level and trust that every member follows the following set of rules:

in each country at any time there should be a balance between energy production and consumption;
each partner should keep to the plans of power capacity exchange;
none of the power systems can cause harm to the power systems of the other countries;
each power system must maintain the frequency level;
each power system must have a certain value of capacity reserve that is used for mutual assistance in case of a failure and for maintaining the frequency level;
the power systems must fully cooperate in restoring normal operation as soon as possible.

The main task of each power system within an integrated power grid is to create favourable conditions for stable and reliable interconnected operation by taking primary, secondary, and tertiary measures to control the frequency and capacity.

Primary, Secondary, and Tertiary Control Systems

In the West European integrated power grid ENTSO-E, the European Network of Transmission System Operators, which includes 42 system operators from 35 European countries, the demands placed on the frequency and capacity control are very high.

Primary control reserve activation

The primary control system uses turbine controllers to ensure the balance between the generated and consumed power. The primary control is triggered if the frequency level deviates from the standard by ± 20 mHz or more. This value is composed of the local frequency measurement accuracy (±10 mHz) and turbine controller insensitivity (±10 mHz). The capacity reserve for the primary frequency control should be 1 per cent of the maximum coverage, with the reserve activation time up to 30 sec (50 per cent in the first 15 sec, and 50 to 100 per cent linearly up to 30 sec).

All the members of integrated power grids are obliged to closely adhere to the regulations and standards established for a particular system, which ensures synchronous operation of an area without unified central control unit.

The main task of the secondary control is ensuring the set levels of capacity exchange between the power systems while maintaining the required frequency. Should perturbations occur in one of the power systems, after the primary control system mobilizes its active capacity reserve, the secondary control system must restore normal operation within 15 minutes. The capacity reserve for secondary control is to make up 5 to 10 per cent of the current load coverage. A minute’s reserve should correspond to the capacity of the largest unit of the grid.

The tertiary control system involves automatic and manual adjustment of the actual generator capacity or load. The reserves of the primary and secondary control systems are to be restored by activating the reserves of the tertiary control system, a process that is to commence within 15 minutes after directions on changing the capacity are issued. The size of the tertiary reserve in each power system should be large enough to maintain the required secondary reserve.

Activating primary, secondary, and tertiary control reserves

The cold or static reserve is to ensure the replacement of the highest-capacity generating unit that has gone out of order.

Another important aspect of the ENTSO-E requirements is maintaining the required grid reliability according to the N-1 criterion, which stipulates that, should any unit of the system go out of order (e.g. a generator, a transformer, a line), it must not endanger the safety of the integrated operation and must not cause cascading power outages.

Operational safety is ensured by complying with the requirements on maintaining the planned modes of real time operation, involving voltage adjustment and reactive power control. Voltage adjustment is done through primary, secondary, and tertiary voltage control.

Development of Major Transnational Power Grids

The West European integrated power grid ENTSO-E (formerly UCTE and UCPTE) was founded in 1951. In 1995 the integrated grid CENTREL, uniting the power systems of Poland, Czech Republic, Hungary and Slovakia, started interconnected operation with UCTE.

The creation of a modern Trans-European integrated power system, such as the synchronous grid ENTSO-E, results from a number of successfully connected national grids in line with the regulations and standards of the wide area synchronous grid. In the case of ENTSO-E this led to the establishment of one of the world’s most synchronous electrical energy areas, characterized by high stability and safety levels.

By the turn of the twenty first century the European continent housed 4 large-scale transnational integrated electricity systems:

UCTE (including CENTREL), or the Western Synchronous Area;
Great Britain and Northern Ireland;
NORDEL, or the Northern Synchronous Area (the national grids of Sweden, Norway, Denmark, Finland and Iceland; the continental part of the Denmark’s national grid was interconnected with UCTE, and the Eastern part – with NORDEL);
the Eastern integrated electricity system, or the Eastern Synchronous Area, which included most CIS countries and the integrated power systems of the Baltic states.

Perspectives on Expanding Wide Area Synchronous Grids

Nuclear power plant in Zaporizhia, Ukraine

Several international projects, facilitating energy cooperation in the Eurasian continent, aspire to create a common electrical power market, which would serve as the basis for a united transcontinental energy area.

It is believed that the development of such projects in conjunction with strengthening the interconnections of ultra-high voltages within the integrated power grids will lead to the establishment of the high-capacity long-distance electricity grid Japan – China – Siberia – Kazakhstan – the European part of Russia – Ukraine – Eastern Europe – Western Europe. This would be a vital step towards creating a large-scale Eurasian synchronous electricity grid, a powerful component of the world’s electricity system.

Being considered is the Baltic ring project, which is to create a powerful integrated electricity grid comprising the national grids of the Scandinavian countries, Baltic states, Russia, Belarus, Poland, and Germany. In the West the Baltic ring is closed with submarine DC cable lines between Sweden and Germany, Norway and Germany, Sweden and Poland; in the East – with the lines of Russia, Belarus, and the Baltic states; in the North – with the high voltage DC link in Vyborg in the North-West of Russia and the lines of the Scandinavian countries. In the South the Baltic ring is closed with multi-substation DC transmission line Russia – Belarus – Poland – Germany, the capacity of which is 4000 MW.

Another project being considered is the transmission line Russia – Japan through the island of Sakhalin, through China and Korea, across the sea straits, and across the Bering strait to interconnect Russia and the USA.

Source (Russian language): http://energetika.in.ua

About KEP

KEP (KharkovEnergoPribor Ltd.) produces high voltage testing equipment, including portable testing instruments and cable test vans, for the world’s leading power engineering companies. The KEP’s product range includes solutions for cable tracing, cable diagnostics and fault locating, testing high voltage instruments and safety gear, and oil dielectric testing.

We at KEP believe that our main task is to translate the customer’s requirements into the top-quality product, combining cutting-edge technology with fundamental high voltage testing principles.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

AC DC Hipot Testing

noreply@blogger.com (Anonymous) — Wed, 22 Feb 2017 12:45:00 +0000

HVT-Family Hipots by KEP

Concerns Associated With DC Testing

DC hipot testing is believed to be harmless to new solid dielectric cables as their insulation is homogenous and allows for an even distribution of electric stress. Also, DC can be safely applied for the installation, acceptance, and maintenance testing of cables with laminated-type insulation.

The most common concerns over DC hipot testing are related to aged cables. Applied to the non-homogenous insulation of such cables, DC is likely to cause space charging at the weak points of the insulation, a very typical problem for extruded cables. In their turn, accumulated space charges can result in electrical treeing and eventual insulation breakdown.

Another limitation of DC withstand testing is the fact that the test polarity cannot be changed during a single test, and no partial discharge can be initiated. Yet, without the partial discharge analysis some of the severe cable insulation defects may be overlooked.

Nevertheless, DC withstand testing is effectively applied to detect insulation errors to do with cable accessories or environmentally-affected interfacial and surface leakage issues.

DC Testing Parameters: Cable Temperature, Test Voltage & Duration

For a DC hipot test to provide accurate results, the cable or cable system under test should be at ambient temperature. This means that if the cable temperature is increased due to having been subjected to substantial load, some time should be allowed for the cable to cool down.

The DC hipot test should be started with test voltage that is up to 80 per cent higher than the cable’s rated ac rms phase-to-phase voltage. It should then be raised, either continuously or in steps, and brought to the maximum test voltage in the time interval of 10 to 60 seconds (this interval may have to be increased for longer cable systems under test); the maximum test voltage should then be maintained for 15 minutes.

Field Test Voltages for Shielded MV Power Cables

System voltage, kV rms, phase-to-phase	System BIL, kV crest	Acceptance test, kV dc, phase-to-ground	Maintenance test, kV dc, phase-to-ground
5	75	28	23
8	95	36	29
15	110	56	46
25	150	75	61
28	170	85	68
35	200	100	75

DC Testing Method

DC withstand testing is performed offline, on a disconnected cable or cable system under test. In case of multiconductor cables, each conductor is tested individually. The other conductors and shields should be grounded. The test lead of the hipot tester is connected to the first conductor under test, and the initial test voltage is supplied and gradually raised to the maximum level.

If the test voltage is increased continuously, it should be done at an even rate. If the test voltage is increased in steps, at least five steps should be made; at each step the technician should wait for the current level to stabilize, with current readings taken at the end of each step, 2 minutes after reaching the maximum test voltage, and at the end of testing.

In most cases steady or decreasing current readings received when fixed voltage was applied indicate that the insulation of the object under test is in an acceptable condition.

A reliable indicator of the insulation quality is the resistance of one of the tree circuit conductors compared to the resistance of the other two conductors. If the ratio of insulation resistance exceeds three to one for cables over 1000 m, it is a sign of the insulation quality deterioration.

Advantages and Disadvantages of DC Withstand Testing

The benefits of the DC dielectric breakdown test include the following:

The lower output capacity of a DC test system compared to an AC test instrument makes DC testing safer for the technician;
The DC withstand test is much safer for the technician than AC testing on highly capacitive objects under test;
DC withstand testing is used to detect insulation errors to do with cable accessories or environmentally-affected interfacial and surface leakage issues;
DC hipot testers accurately display the amount of true leakage current of the cable or cable system under test.

Yet, DC withstand testing has a number of drawbacks:

The cable or cable system under test has to be discharged after testing;
DC withstand testing is potentially destructive for the insulation of service age cables;
Some serious insulation errors cannot be revealed with DC dielectric breakdown testing.

So, DC hipot testing is still widely applied for the acceptance testing of newly-installed cables. Yet, when it comes to maintenance testing done in the field, VLF hipots are more commonly used.

AC versus DC Testing

AC withstand testing is typically used by cable producers when performing the installation testing of new cables. The AC hipot test is a Pass/Fail or Go/No-Go test, during which the technician raises the test voltage to a certain maximum value to check whether the object being tested can withstand the applied voltage, and therefore passes the AC test, or fails it. AC hipot testing is widely used to see whether the equipment complies with the applicable standard.

In contrast, DC testing provides more information on the cable or cable system under test, giving the ability to measure leakage current and calculate the insulation resistance.

Another difference is the size, and therefore cost, of AC testers and DC testers, with the former being substantially larger and more expensive than their DC analogues. This is explained by the fact that AC testers supply a much larger charging current than DC testers do.

The strong advantages of DC over AC testing are that DC testers are smaller, more affordable, safer due to supplying less current, and give information on real leakage current. On the negative side, with DC testers there is a need to ramp up the test voltage and to discharge the object under test after testing.

The benefits of AC versus DC testing are that AC testing does not require ramp voltage and the object being tested does not need discharging. However, due to their size AC test sets are usually not practical for field testing; besides, the high current they supply present a safety hazard for the operator.

AC DC Hipot Testers by KEP

AC DC Hipot Tester HVTS-70/50

Understanding that today’s cable testing conditions require flexibility in terms of hipot testing method choice, KEP offers the portable test systems AC DC Hipot Tester HVT-70/50 with oil-insulated high voltage unit and AC DC Hipot Tester HVTS-70/50 with SF-6 insulated high voltage unit.

KEP’s high voltage test systems HVT-70/50 and HVTS-70/50 perform DC high potential testing of power cables (IEC 60502-2) up to 70 kV, power cables accessories (IEC 61442) as well as AC high potential testing, up to 50 kV at 50 Hz, of switchgear, reclosers, dielectric insulators, highvoltage dischargers (arresters), busbars and other dielectric materials with relatively low electric capacitance.

The main features of the HVT-70/50 and HVTS-70/50 AC DC hipot testers include:

AC (up to 50 kV) and DC (up to 70 kV) modes
Compact and portable design
Exceptionally high safety level due to the new safety interlock and two-operator mode features
Internal memory
Auto and manual modes
Wireless test data exchange with a PC via optional Bluetooth

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

VLF Withstand Test. Introduction to Hipot Cable Testing

noreply@blogger.com (Anonymous) — Thu, 16 Feb 2017 07:57:00 +0000

KEP Product Catalogue

What is VLF Hipot Testing

Withstand or hipot testing is used to evaluate the condition of a cable insulation during installation, acceptance, or maintenance testing. As a result of a hipot test, at the point of an insulation defect an electrical tree will start to progress, create the insulation breakdown and make it possible for the technician to pinpoint the faulted place.

As a result of a hipot test, at the point of an insulation defect an electrical tree will start to progress, create the insulation breakdown and make it possible for the technician to pinpoint the faulted place.

The main focus of this article is the very low frequency (VLF) withstand cable test, which essentially is a type of AC hipot test conducted at a frequency rate of 0.01 to 1.00 Hz. Due to a significant drop in the operation frequency compared to AC hipot testing, done at 50 or 60 Hz, a VLF hipot tester is much smaller than a typical AC hipot test set, and thus is widely applicable for field usage.

Main VLF Hipot Testing Parameters: Waveform, Voltage, Duration

The typical waveforms for VLF testing include the sinewave, squarewave, and cosine-rectangular (trapezoidal) wave. The sinewave, or sinusoidal voltage, is the same as the voltage used by AC power systems. Out of the three mentioned waveforms, the sinewave is found to be the most efficient for cable testing as it causes the electrical tree to progress at the fastest rate, which results in shorter test times.

IEEE 400.2 guide stipulates that the test voltage should be 2.0 to 3.0 times the cables’ normal line to ground voltage. Since maintenance testing is done on service age cables, the recommended voltage is 80 per cent of that used for installation/acceptance testing. If there is a need to perform several test cycles, it may be reasonable to decrease the testing voltage by a further 20 per cent. The table below reflects the IEEE 400.2 guidelines as to the optimal testing sinewave voltage for 5 kV to 35 kV cables.

Table 1. VLF test voltage

Cable rms voltage	Installation rms / peak voltage	Acceptance rms / peak voltage	Maintenance rms / peak voltage
5 kV	9 / 13 kV	10 / 14 kV	7 / 10 kV
8 kV	11 / 16 kV	13 / 18 kV	10 / 14 kV
15 kV	18 / 25 kV	20 / 28 kV	16 / 22 kV
25 kV	27 / 38 kV	31 / 44 kV	23 / 33 kV
35 kV	39 / 55 kV	44 / 62 kV	33 / 47 kV

The advised testing time is 60 minutes at 0.1 Hz on new cables, and 30 minutes at 0.1 Hz on service age cables; it is recommended that the withstand testing time during maintenance testing should be extended to 60 minutes at 0.1 Hz if the circuit in question is of special importance.

VLF Testing Method

VLF testing is performed on offline cables, that is, the cable under test should be disconnected from the power system, and properly grounded. The VLF tester is then connected to the cable under test, and the required test voltage is set.

If the cable under test passes the VLF testing, the voltage should be decreased to zero, the cable under test and the VLF instrument should be discharged, and the cable should be grounded.
If the cable under test fails the test, the test voltage drops down to zero on its own. The VLF tester should be switched off for the cable and the tester to discharge, and the cable should be grounded. After that, the fault or faults can be found with fault locating instruments and repaired, or the respective cable sections are replaced.

Connection Setup for a VLF Cable

Advantages and Disadvantages of VLF Cable Testing

The strong points of VLF cable testing include the following:

VLF cable testing is applicable for extruded polyethylene, laminated paper, and mixed insulation;
the small size of the VLF test set is perfect for field testing;
VLF hipot testing can be done on both new and service age cables, which means that it can be used for installation, acceptance, and maintenance testing;
With the right voltage and testing time, VLF testing is not destructive for less severe insulation defects that could remain dormant for a long time and not impede the cable performance. Yet, it is efficient for locating more severe insulation defects that are likely to cause cable faults in the nearest future;
Combined with standard cable diagnostics equipment, the VLF test set can be used for diagnostic testing.

At the same time, the difficulties associated with VLF hipot testing are these:

VLF withstand testing may not provide conclusive results if the insulation is significantly damaged by water treeing or has partial discharges. In this situation, it is recommended that VLF testing should be combined with other diagnostic testing methods;
VLF testing with very high testing voltage at a frequency below 0.01 Hz may cause space charges in extruded polyethylene insulation;
VLF cable testing is done on offline cables only.

To sum up, although VLF withstand testing is attributed to destructive cable testing as it causes severe defects to initiate treeing and break down the insulation, the VLF test nevertheless does not harm good insulation. So, VLF hipot testing performed with alternating sinusoidal voltage best meets the testing purpose of locating and removing several defects in insulation that is mostly of good quality.

Alexei Tiatiushkin
Marketing manager
KharkovEnergoPribor Ltd.
marketing@keppowertesting.uk
http://www.kep.ua

Undervoltage and Overvoltage DC Testing. Short Guide to Hipot Tests

noreply@blogger.com (Anonymous) — Mon, 06 Feb 2017 11:36:00 +0000

High voltage unit HVTS-70/50

There are several methods for the field testing of underground electric power cables which are grouped under the category of Type 1 Tests. These are intended to detect defects in the insulation of the cable system in order to improve the service reliability after the defective part is removed and appropriate repairs are performed. These tests are usually achieved by application of moderately increased voltage across the insulation for a prescribed duration of time. Such tests are categorized as a pass or fail, go or no go type of a test.

Type 1 Tests typically involve one of the following:

the insulation resistance test performed with a standard megohmmeter, also known as undervoltage test;
the DC high potential test or DC hipot test;
the very low frequency high potentials test (VLF hipot test);
the AC high potential test which is performed at power frequency (50 hertz or 60 hertz).

It should be noted that due to the size of the equipment required for an AC hipot test on a very high capacitive device under test such as cable, normally the power frequency test is done at the factory, in cable labs, but is not used in the field.

Undervoltage tests utilizing DC voltage

Undervoltage tests are typically performed with megahometer. Since the test uses voltages under the rating of the insulation, the test is considered to be a nondestructive test and does not produce any of the harmful effects associated with a high voltage DC test. Insulation tests electrically stimulate the insulation and measure the response. Depending upon that response conclusions are drawn about the condition of the insulation.

What we need to know is that if perfect insulation existed, there would be no flow of electrical current through the insulation to ground. But since no insulation has infinite resistance, there is always some leakage current flowing through the insulation. While a small amount of current leaking through a good insulation is not a problem, difficulties arise when the insulation begins to deteriorate, and the leakage current begins to increase.

The insulation resistance test measures the resistance of the insulation material to the flow of the leakage current, helping to assess the condition of the insulation. This type of test allows either to measure the resistance or the flow of the leakage current.

Overvoltage testing utilizing DC voltage

For years high voltage DC testing has been a traditionally accepted method for judging the serviceability of MV cables. DC hipots or DC high potential tests have worked well as a withstand and condition assessment test for paper insulated led-covered PILC cables. When plastic insulation cables were first introduced, DC was still the preferred measurement method.

As time moved on, plastic insulated cables became more abundant and began showing aging effects and service aging. DC continued to be the dominant test, but concerns began to grow over the effectiveness of this test. Studies showed that while not causing any damage to new cables, DC hipot testing has a detrimental effect on service age cables on account of accelerating treeing effects.

Hipot Test Set HVTS-70/50

Currently, most standards continue to include DC testing as an acceptance test on newly installed extruded dielectrics, and almost all of the recommended practices have abandoned the use of DC testing for maintenance purposes, or particularly when the cable has reached service age (is over five years of age).

To locate a cable fault with DC hipot testing, the technician needs to find the point where current leaks through the faulted insulation, and for electricity to leak, it requires a conductive path. In other words, two wires should be exposed, or there should be a wire and some other metal like the cable shield. So, in hipot testing, voltage is increased to cause leaking or arcing between exposed wires or cables, which helps to catch errors that otherwise would be missed.

Yet, there are a few reservations regarding dielectric failures that should be taken into account. It is possible for an insulation breach that results in a dielectric failure to self-heal, meaning that subsequent hipot test may actually pass. In addition, it is possible for small solder slivers which caused dielectric failures to be vaporized by the hipot test, meaning that subsequent hipot tests again may actually pass. It is also possible for these small solder slivers to leave a carbon track or be metallic sized when they are vaporized by the hipot test, meaning that subsequent hipot tests will fail. Because of these issues it is recommended that any cable that fails a hipot test be closely checked and retested at least twice.

To sum up, DC hipot testing is still widely applied for acceptance testing. Yet, when it comes to maintenance testing done in the field, VLF hipots are more commonly used, which will be discussed in more detail in the next article.

Alexei Tiatiushkin

Marketing manager

KharkovEnergoPribor Ltd.

marketing@keppowertesting.uk

http://www.kep.ua

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