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Measurement of insulation resistance on a power transformer

2011-10-22T13:00:00.000-07:00

Measurement of insulation resistance

These measurements aimed to determine the condition of insulation between the windings to ground or between two windings. A common method is to provide a dc voltage and represents the condition of the unit megohm insulation. Measured insulation resistance is a function of leakage current that penetrates through the insulation or through the leak in the external surface. Insulation resistance testing may be influenced temperature, humidity and leakage paths on the external surfaces such as dirt on the bushing or insulator. Megaohm meters typically have a capacity of testing 500, 1000 or 2500 V dc.

Mega Ohm meter gauge

Polarization Index Test

The purpose of the polarization index test is to ensure the equipment is operated or even feasible to do overvoltage test. Polarization index is the ratio of insulation resistance at the 10th minute by minute to 1 with a constant voltage.

Total current that arise when providing a dc voltage steady state consists of:

1. Charging current due to the nature of the measured capacitance of the insulation. This flows down from the maximum value to zero very quickly.
2. Absorption of molecular charge current due to shifting in isolation. These transient currents disappear to zero more slowly
3. leakage current is a conduction current in insulating concrete. Leakage current varies depending on the test voltage. Also includes a leakage current due to leakage at the surface due to contamination.

Description:
R = insulation resistance (MΩ)

C = 1.5 for oil filled transformers at a temperature of 20o C 30.0 to untanked oil-impregnated transformers

E = voltage rating (V) on the inter-phase delta connection, the phase neutral star connection

kVA = rating capacity of the tested winding.

Insulation condition based on the index of polarization

Dissolved Gas Analysis (DGA) on power transformers

2011-10-21T13:00:00.000-07:00

Transformer as a high-voltage equipment can not be separated from the possibility of having an abnormal condition, where the trigger can come from internal or external transformer. These abnormalities will have an impact on the performance of the transformer. In general, the impact / result can be overheating, corona and arcing.

One method to determine the presence or absence of abnormalities of the transformer is to determine the impact of abnormalities of the transformer itself. To determine the impact of abnormalities in the methods used transformer DGA (Dissolved gas analysis).

In the event of abnormalities of the transformer, insulating oil as the hydrocarbon chain will break down due to the amount of energy will shape abnormalities and hydrocarbon gases are soluble in oil insulation itself. DGA is basically a process to calculate levels / values of the hydrocarbon gases are formed due to abnormalities. From the composition of the content / value of the gases that can predict what the effects of abnormalities in the transformer, if overheating, arcing or corona.

Gas gas detected from the test results DGA is H2 (hydrogen), CH4 (Methane), N2 (Nitrogen), O2 (Oxygen), CO (Carbon Monoxide), CO2 (Carbondioksida), C2H4 (Ethylene), C2H6 (Ethane), C2H2 (Acetylene).

Broadly speaking, the gas dissolved gases in transformer insulating oil will be extracted / separated from the insulating oil itself first so that the gas will be described and known levels.

Type of head space gas extractor

After separate between the gas with oil, gas will be described again by type of its gas by using chromatography methods.

Scheme Chromatography

Gas that has broken down will be detected by the detector signal. This was the signal that will be used to determine the amount of gas taking into account the broad levels of each signal of each gas. This test refers to the standard ASTM D 3613

The signal from the gas detected by the detector gas

DGA test equipment - with this type of extractor stripper

Power Transformers Part

2011-10-21T01:00:00.000-07:00

Power Transformers Part

1. Refrigerant

The temperature at which the transformer is operating will be influenced by the quality of the network voltage, losses in the transformer itself and the ambient temperature. High operating temperatures will cause damage to the transformer insulation paper. Therefore, effective cooling is needed.

Transformer insulating oil in addition to the isolation medium also serves as a coolant. At the time of the oil circulates, the heat emanating from the entanglement will be brought by the oil circulation on track and will be cooled on the fin - fin radiator. The cooling process can be aided by a fan and circulation pump in order to improve cooling efficiency.

Power Transformers Radiator

2. Oil preservation & expansion (Conservator)

When the operating temperature rise in transformer oil, insulation will expand so that its volume increases. Conversely when the operating temperature decreases, then the oil will shrink and the volume of oil will go down. Conservators used to accommodate the transformer oil at mengalamui temperature rise.


Power Transformers Conservator

Silica gel

To avoid the transformer oil does not deal directly with outside air, then the current conservator designed using brether bag / rubber bag, which is a kind of rubber balloon that is placed inside the conservator tank.

Construction conservator with rubber bag

3. Dielectric (insulating transformer oil & Insulation paper)

Isolation transformer oil

Insulating oil in transformers serve as insulation, cooling and protecting the entanglement of oxidation. Transformer insulating oil is mineral oil which is generally divided into three types, namely paraffinic, and aromatic napthanik. Between the three types of base oils should not be done mixing because it has physical and chemical properties are different.

Isolation Transformer Oil

Paper insulation transformer

Isolation papers serve as insulation, giving the distance, and has the mechanical ability.

Copper-coated insulation paper

Part of the Bushing

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Broadly speaking, the bushing can be divided into four main sections namely insulation, conductor, clamp connections, and accessories. Isolation of the bushing consists of two types of oil impregnated paper and resin impregnated paper. In this type of oil impregnated paper insulation used is insulating paper and insulating oil while in the type of resin impregnated paper insulation used is the paper insulation and resins.

Paper insulation on the bushing (oil impregnated paper bushings)

Bushing conductor insulation coated paper

There are other types of conductors on the bushing is a hollow conductor in which there is an iron binding or hole in the middle penegang main conductor, solid and flexible conductor leads.

Is a means of fastening clamp connection between the stud bushing with a conductor Conductor bushing out.

Accessories consist of indications of oil bushings, seals or gaskets and tap testing. Seal or gasket in bushing mounting flange located at the bottom.

Gasket / seal between the flange bushings with transformer body

Bushing oil level indicator

Section - parts transformer and its function

2011-10-19T13:22:00.000-07:00

Iron core

1 Electromagnetic Circuit (iron core)
Iron core is used as a medium course of flux caused by the induction of alternating current to the coil that surrounds the iron core so as to induce a return to the other coil. Formed from the plate - a thin iron plates insulated in such a way that the stacking.

2 Current carying circuit (Winding)
Winding consists of insulated copper rod that surrounds the iron core, which when alternating current flows
in the copper windings, iron core will be induced and cause a magnetic flux.

winding transformer

3. Bushing
Bushing is a means of liaison between the entanglement with outside networks. Bushing consists of a conductor is enclosed by an insulator. Serves as an insulator between the conductor insulation bushing with tank main body of the transformer.

bushing transformer

Types of Electrical Plugs and Sockets

2011-10-18T13:26:00.000-07:00

Electrical plug and socket 2 pin was originally invented by Harvey Hubbell and patented in 1904. Hubbell's work is also a reference to the manufacture of plug and socket and by the year 1915 after its use more widespread, although in the years 1920s home and commercial appliances still use a screw-type lamp socket base Edison.

Then plug 3 pin was created by Albert Büttner in 1926 and obtain patents from German patent agency (ED 370 538), his work is known as "Schuko". But there is also the creator of this 3 pin plug, which is Philip F. Labre, during he was still studying at Milwaukee Vocational School (MSOE) and obtain patents from the United States on June 5, 1928. Anyone penenmunya, discovery 3 pin plug or plugs this is something that is very unusual, because the aspect of human safety, so that the plug or electrical outlet of this type became the standard in almost all countries to date.

Types of Plug and Socket

The types of plug and socket are classified based on the voltage and frequency used in a country, so it can be said there are only two types are based on this classification, namely:

• For voltage 110-220 volts at a frequency of 60 hz

• For voltage 220-240 volts at a frequency of 50 hz

There are also some countries that use the plug and socket for both, see the map of the use of voltage and frequency of electricity in the world below. (Click image to view larger map)

While based on the safety plug and socket are classified into:

• Without grounding, ungrounded. Usually for a 2 pin plug, and according to the IEC standard is a class-II

• With grounding, grounded. Usually for a 3 pin plug, and according to the IEC standard is the class-I

• With grounding and fuses, fuse and grounded. Usually for a 3 pin plug.

Based on the above classifications, then the plug and socket of each state may vary, and generally the type and standard of the plug and socket are:

1. Type A, NEMA 1-15

• 2 pins with a standard NEMA 1-15 (North American 15 A/125 V ungrounded) plug type A can also be used on socket type B.

• JISC 8303, Class II (Japanese 15 A/100 V ungrounded) is a standard plug and socket in Japan are similar to the plug and socket type A, and also must pass the test of MITI (Ministry of International Trade and Industry) and JIS (Japanese Industrial Standards).

2. Type B, NEMA 5-15

• 3 pin with a standard NEMA 5-15 (North American 15 A/125 V grounded), is a plug and socket standard in North America (Canada, the United States and Mexico), also used in Central America, Caribbean, Columbia, Ecuador, Venezuela and part of Brazil, Japan, Taiwan and Saudi Arabia

• 3 pin with a standard NEMA 5-20 (North American 20 A/125 V grounded), is used for the installation of home dates beginning in 1992, with a socket slot model T.

• JIS C 8303, Class I (Japanese 15 A/100 V grounded)

3. Type C, CEE 7 / 16

• CEE 7 / 16 (Europlug 2.5 A/250 V ungrounded), Plug is commonly used in Class II applications (ungrounded). Plug This plug is one of the most widely used internationally because it fits with any socket that can receive contacts 4.0 - 4.8 mm with a separation distance of 19 mm. This plug can be used in all European countries except Britain and Ireland (because the UK / Ireland had its own standards). But the use of this plug is generally limited to the use of Class II applications that require currents below 2.5 A and unpolarized.

• CEE 7 / 17 (German / French 16 A/250 V ungrounded), its size is almost the same as the type E and F, the plug was coated with rubber or plastic. Used also in south korea for electrical equipment that is not grounded and in italian categorized by Italian standards CEI 23-5

• BS 4573 (UK shaver), used in Britain to use the tools razor or shaver in the bathroom. The distance between the pins with 5.08 mm pin length 15.88 mm and has been used in English since the 1960s.

• Soviet plug (6 A/250 V ungrounded), almost the same as the French type E and CEE7/17

4. Type D, BS 546

• BS 546 (United Kingdom, 5 A/250 V grounded), equivalent to IA6A3 (India), rated at 6A / 250V

• BS 546 (United Kingdom, 15 A/250 V grounded), equivalent to IA16A3 (India) & SABS 164 (South Africa), rated at 16A / 250V

5. Type E, CEE 7 / 5 (French type E)

6. Type F, CEE 7 / 4

• CEE 7 / 4 (German "Schuko" 16 A/250 V grounded)

7396 • GOST (Russian 10 A/250 V grounded)

7. Type E / F Hybrid, CEE 7 / 7

CEE 7 / 7 (French / German 16 A/250 V grounded)

8. Type G, BS 1363

BS 1363 (British A/230-240 13 V 50 Hz grounded and Fused), equivalent to IS 401 & 411 (Ireland), MS 589 (Malaysia) and SS 145 (Singapore), 2203 SASO (Saudi Arabia)

9. Type H, SI 32

• SI 32 (Israeli 16 A/250 V grounded)

• 3 pin plug TIS166 Thai-2549 (2006)

10. Type I, NZS 3112

• AS / NZS 3112 (Australasian 10 A/240 V)

• CPCS-CCC (Chinese 10 A/250 V)

• IRAM 2073 (Argentinian 10 A/250 V)

11. Type J, SEV 1011 (Swiss 10 A/250 V)

12. Type K, Section 107-2

Section 107-2, D1 (Danish 13 A/250 V earthed)

13. Type L, 23-16/VII CEI

• 23-16/VII CEI (Italian 10 A/250 V and 16 A/250 V)

• 23-16/VII CEI (Italian 10 A/250 V)

• 23-16/VII CEI (Italian 16 A/250 V)

14. Type M, BS 546 (South African 15 A/250 V)

15. Getting category yet

IEC 60906-1 (Brazilian 10 A and 20A / 250 V)

Conclusion:

There are 14 plug and socket standard pattern used throughout the world, both for applications as Class I (grounded) and Class II (ungrounded), with current ratings ranging from 2.5 to 16 A. These standards are the standards of the United States, North America, Argentina, Australia, Mainland Europe, Europlug, China, Denmark, India / South Africa, Israel, Italy, Japan, Switzerland, and UK / Ireland.

Map below will explain about the countries in the world and plug & socket type used

POWER TRANSFORMERS

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1. Definition and function POWER TRANSFORMERS

The transformer is an electrical device which serves to channel the power / energy from high voltage to low voltage or vice versa.The transformer uses the principle of faraday law of induction andthe Lorentz law in distributing power, where the alternating currentthat flows around an iron core iron core then it will turn into a magnet. And if the magnet is surrounded by a winding it on both ends of the windings is the potential difference will occur (Figure1.1).

Figure 1.1. Alternating current around an iron core

Current flowing in the primary winding will induce iron coretransformer that will flow in the iron core and the magnetic flux of this magnetic flux will induce a secondary winding secondarywinding so that at the end there

will be a potential difference(Figure 1.2).

Figure 1.2. The working principle of transformer

2 Types of power transformer

Based on the power transformer function can be divided into:
• Transformer power
• The transformer substation / distribution
• the distribution transformer

Power transformers for the distribution function can be dividedinto:
• a large transformer
• Transformer is
• a small transformer

large transformer

Transformer Tap Changer

2011-10-05T18:17:00.000-07:00

The tap changer is a tool changer for voltage transformation ratio of secondary operations that are better than the network voltage / primary changes.

There are two ways of working tap changer:
1. Changing the tap in a state of no-load transformer. Tap changer that can only operate to move the transformer tap transformer in a state of no load, called "Off Load Tap Changer" and can only be operated manually

2. In a state transformer tap changing under load. Tap changer that can operate to move the tap transformer, the transformer under load condition, called "On Load Tap Changer (OLTC)" and can be operated manually or automatically

Transformer installed in substations in general use tap changer that can be operated in a state of the transformer under load and mounted on the primary side. While penaik voltage transformer in a power transformer capacity or in small, generally using the tap changer is operated only during power transformer no-load.

OLTC composed of:
1. Selector Switch
2. diverter switch
3. transition resistors

To isolate the transformer from the body (ground) and to reduce heat during the process of moving the tap, then OLTC immersed in insulating oil are usually separated from the main isolation transformer oil (there are some transformers that compartemennya become one with the main tank).

Because the transfer process in the oil tap relationships happened electrical phenomena, mechanical, chemical and heat, the insulation OLTC oil quality will quickly decline. depending on the amount of work and the presence of abnormalities in the OLTC

How to Bow Fire occurred in Circuit Breaker

2011-10-04T06:07:00.000-07:00

How to Bow Fire Occurred in Circuit Breaker? At the time of termination or a circuit linking the power systems (circuit breaker) will occur arc, it happens because at the time of circuit breaker contacts are separated, the potential difference between the contacts will cause the electric field between the contact , as shown in the picture below.

The current that previously flowed to the contact will heat up the contacts and produce thermic emission at the contact surface. While the electric field of high field emissions led to contact the cathode (K). Both of these emissions are produced free electrons are very much and move toward the anode contact (A). These electrons hit the media a neutral molecule of positive isolation of the region, these collisions will cause the ionization process. Thus, the number of free electrons to the anode will be growing and emerging results of ionization of positive ions moving toward the cathode, transfer of free electrons to the anode current rise and heat the anode contact.

Positive ions arriving at the cathode contact will cause two different effects. If contact is made of high melting point materials, such as tungsten or carbon, then the positive ions will be cause heating at the cathode. As a result, emissions increased thermic. If contact is made from low melting point material, eg copper, positive ions will cause high field emission. The results of this thermic emissions and high field emissions will perpetuate the ionization process, so that the charge transfer between the contacts continued and is called the arc.

To extinguish the arc is necessary efforts that could cause deionization process, among others the following manner:

1. Blow air into the sidelines of contact, so the particles ionisai results kept out of contact between.

2. Oil spraying insulation into the arc to give greater opportunities for recombination processes.

3. Arc cutting with a veil of isolation or metal screens, giving greater opportunities for recombination processes.

4. Create a contact separation medium of electronegative gases, so that free electrons captured by neutral gas molecules.

If the reduction of charged particles due to deionization process more than the addition of the charge due to the ionization process, then the arc will be extinguished. When the arc goes out, in between the contacts will remain the electric field exposure. If an exposure occurs when the electric field that is greater than the dielectric strength of insulating media contacts, the arcing will occur again.

What is SCADA ?

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SCADA stands for Supervisory Control and Data Acquisition.

The function is for an operator in the transmission of electricity, called the dispatcher, able to perform and take advantage of the following things:

- Telemetering (TM)

Dispatchers use TM to the needs of monitoring meters, both in MW of real power, reactive power in MVAr, voltage in kV, and currents in A. Thus the dispatcher can monitor the meters of the whole network just by sitting in place, of course with the help of other supporting equipment such as phones.

- Telesinyal (TS)

Dispatchers can use TS to get an indication of all alarms and conditions of certain equipment that could be opened (open) and closed (close)

Telecontrol Scada

- Telecontrol (TC)

Dispatchers can conduct remote control, simply by pressing a button, to open or close the electrical power system equipment For the purposes aforesaid, a dispatcher will be assisted by an integrated SCADA system which is in the room

special, and called the Control Center. The room is joined with a special room to put the computers called the Master Station.

SCADA-operated in the control center includes a variety of applications yaitusebagai follows:

- Data acquisition

- Supervisory Control

- Monitoring data, event processing (events) and alarms

- Calculate data

- Tagging (tagging)

- Recording data

- Reporting

Besides the need for a control center, on the other side should put up the infrastructure and other supporting equipment, namely telecommunications, Remote Terminal Unit (RTU), transducer, and so forth. Telecommunications used as a data and voice communications between the control center

the site (location). RTU is used as a terminal unit for control, data acquisition, and the supervision of a substation, and then sends that data to the control center in question.

Static and Digital Relays

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1. S TAT IC RE L AY S

The term ‘static’ implies that the relay has no moving parts. This is not strictly the case for a static relay, as the output contacts are still generally attracted armature relays. In a protection relay, the term ‘static’ refers to the absence of moving parts to create the relay characteristic.

Circuit board of static relay

Introduction of static relays began in the early 1960’s. Their design is based on the use of analogue electronic devices instead of coils and magnets to create the relay

characteristic. Early versions used discrete devices such as transistors and diodes in conjunction with resistors, capacitors, inductors, etc., but advances in electronics enabled the use of linear and digital integrated circuits in later versions for signal processing and implementation of logic functions. While basic circuits may be common to a number of relays, the packaging was still essentially restricted to a single protection function per case, while complex functions required several cases of hardware suitably interconnected. User programming was restricted to the basic functions of adjustment of relay characteristic curves. They therefore can be viewed in simple terms as an analogue electronic replacement for electromechanical relays, with some additional flexibility in settings and some saving in space requirements. In some cases, relay burden is reduced,

making for reduced CT/VT output requirements.

A number of design problems had to be solved with static relays. In particular, the relays generally require a reliable source of d.c. power and measures to prevent damage to vulnerable electronic circuits had to be devised. Substation environments are particularly hostile to electronic circuits due to electrical interference of various forms that are commonly found (e.g. switching operations and the effect of faults). While it is possible to arrange for the d.c. supply to be generated from the measured quantities of the relay, this has the disadvantage of increasing the burden on the CT’s or VT’s, and there will be a minimum primary current or voltage below which the relay will not operate. This directly affects the possible sensitivity of the relay. So provision of an independent, highly reliable and secure source of relay power supply was an important consideration. To prevent maloperation or destruction of electronic devices during faults or switching operations, sensitive circuitry is housed in a shielded case to exclude common mode

and radiated interference. The devices may also be sensitive to static charge, requiring special precautions during handling, as damage from this cause may not be immediately apparent, but become apparent later in the form of premature failure of the relay. Therefore, radically different relay manufacturing facilities are required compared to electromechanical relays. Calibration and repair is no longer a task performed in the field without specialised equipment.

Selection of static relays

2. D I G I TA L R E L AY S

Digital protection relays introduced a step change intechnology.Microprocessors and microcontrollers replaced analogue circuits used in static relays toimplement relay functions. Early examples began to be introduced into service around 1980, and, withimprovements in processing capacity, can still be regarded as current technology for many relay applications.However, such technology will be completely superseded within the next five years by numerical relays.

digital relay

Compared to static relays, digital relays introduce A/D conversion of all measured analogue quantities and use a microprocessor to implement the protection algorithm.

The microprocessor may use some kind of counting technique, or use the Discrete Fourier Transform (DFT) to implement the algorithm.However, the typical

microprocessors used have limited processing capacity and memory compared to that provided in numerical relays. The functionality tends therefore to be limited

and restricted largely to the protection function itself. Additional functionality compared to that provided by an electromechanical or static relay is usually available,

typically taking the form of a wider range of settings, and greater accuracy. A communications link to a remote computer may also be provided. The limited power of the microprocessors used in digital relays restricts the number of samples of the waveform that can be measured per cycle. This, in turn, limits the speed of operation of the relay in certain applications. Therefore, a digital relay for a particular protection

function may have a longer operation time than the static relay equivalent. However, the extra time is not significant in terms of overall tripping time and possible effects of power system stability.

Relay Technology

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The last thirty years have seen enormous changes in relay technology. The electromechanical relay in all of its different forms has been replaced successively by static, digital and numerical relays, each change bringing with it reductions and size and improvements in functionality.

At the same time, reliability levels have been maintained or even improved and availability significantly increased due to techniques not available with older relay types.

This represents a tremendous achievement for all those involved in relay design and manufacture.

1. ELECTROMECHANICAL RE LAYS

These relays were the earliest forms of relay used for the protection of power systems, and they date back nearly 100 years. They work on the principle of a mechanical force causing operation of a relay contact in response to a stimulus. The mechanical force is generated through current flow in one or more windings on a magnetic core or cores, hence the term electromechanical relay. The principle advantage of such relays is that they provide galvanic isolation between the inputs and outputs in a simple, cheap and reliable form – therefore for simple on/off switching functions where the output contacts

have to carry substantial currents, they are still used. Electromechanical relays can be classified into several different types as follows:

a. attracted armature

b. moving coil

c. induction

d. thermal

e. motor operated

f. mechanical

However, only attracted armature types have significant application at this time, all other types having been superseded by more modern equivalents.

2. Attracted Armature Relays

These generally consist of an iron-cored electromagnet that attracts a hinged armature when energised. A restoring force is provided by means of a spring or gravity so that the armature will return to its original position when the electromagnet is de-energised.

Typical forms of an attracted armature relay are shown in Figure 1. Movement of the armature causes contact

closure or opening, the armature either carrying a moving contact that engages with a fixed one, or causes a rod to move that brings two contacts together. It is very easy to mount multiple contacts in rows or stacks, and hence cause a single input to actuate a number of outputs. The contacts can be made quite robust and

hence able to make, carry and break relatively large currents under quite onerous conditions (highly inductive circuits). This is still a significant advantage of this type of relay that ensures its continued use

Typical attracted armature relays

The energising quantity can be either an a.c. or a d.c. current. If an a.c. current is used, means must beprovided to prevent the chatter that would occur from the flux passing through zero every half cycle. A common solution to the problem is to split the magnetic

pole and provide a copper loop round one half. The flux change is now phase-shifted in this pole, so that at no time is the total flux equal to zero. Conversely, for relays

energised using a d.c. current, remanent flux may prevent the relay from releasing when the actuating current is removed. This can be avoided by preventing the armature from contacting the electromagnet by a non-magnetic stop, or constructing the electromagnet using a material with very low remanent flux properties.

Operating speed, power consumption and the number and type of contacts required are a function of the design. The typical attracted armature relay has an operating speed of between 100ms and 400ms, but reed relays (whose use spanned a relatively short period in the history of protection relays) with light current contacts can be designed to have an operating time of as little as 1msec. Operating power is typically 0.05-0.2 watts, but could be as large as 80 watts for a relay with several heavy-duty contacts and a high degree of resistance to mechanical shock.

Some applications require the use of a polarised relay. This can be simply achieved by adding a permanent magnet to the basic electromagnet. Both self-reset and bi-stable

forms can be achieved. Figure 2 shows the basic construction. One possible example of use is to provide very fast operating times for a single contact, speeds of less than 1ms being possible.

Typical polarised relay

GROUNDING NEUTRAL POWER SYSTEM

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In 1910, electric power systems are not grounded. This is due in the electric power systems is still small, so if there is fault current phase to ground fault current is still small, and usually less than 5 amperes. In general, if the fault current of 5 amperes or less, an electric arc that arise in contacts between the disturbed and the ground wire can still be extinguished itself.

But the systems of power that increasingly large both in length and voltage. Thus the currents that arise in the event the greater the soil disturbance and electric arc that can no longer go out alone. Additional symptoms longer arc of land or ground arcing increasingly prominent. Symptoms of an arc of land is a process of termination (clearing) and at-re (restriking) from the electric arc repeatedly. This phenomenon is very dangerous because it may cause high transient overvoltages that can damage the equipment.

System grounded in a state of disorder the ground wire

The methods of neutral earthing of the power systems are as follows:

1. Grounding through the resistance (resistance grounding).

2. Grounding through the reactor (reactor grounding).

3. Grounding without impedance (solid grounding).

4. Effective earthing (grounding effective).

5. With an impedance earthing reactors can be fickle (resonant grounding) or ground with Petersen coil.

In the systems are not grounded or delta system, the fault current depends on the capacitive impedance ZA, ZB and ZC, namely the capacitive impedance of each wire-phase to ground.

However, when the system is earthed fault current is no longer dependent only from impedance capacitive wires but also depends on the impedance earthing equipment and tansformator.

Unless the earth with Petersen coil, the impedance earthing device is very small compared to the capacitive impedance, or in other words it is no longer current noise depends on the impedance.

So with a grounded neutral fault current system clearly becomes larger than the current disruption in the delta system, but instead limit the voltage on the phases are not disrupted. So in determining the earthing impedance must be observed that the relationship between the large fault current and voltage that may arise.

System grounded in the disturbanceground wire

Working Principle Arrester

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Protective equipment is the most complete arrester (lightning arresters; kada-sometimes also called a surge diverter). In essence this arrester consists of two elements: between fire (spark gap) and no linear prisoners or detainees valve (valve resistors), both connected in series

Upper and lower limits of the spark voltage is determined by the maximum system voltage and by the isolation level of protected equipment. Arresters actually consists of three elements: fire interrupted, prisoners or detainees faucet valves and system settings or voltage division (grading system).

As stated in advance, if the problem only protects the insulation against the danger of damage due to interference between the rod then just used that allows the spark when the voltage reaches a state of danger. In this case, the voltage alternating system will maintain the arc until the load breaker is opened. With the connect between this fire with a prisoner, then maybe the fire can be extinguished. But if the prisoner has a fixed price, then the voltage falls becomes greater, so the intention to abolish the voltage is less accomplished, and the purpose of protecting the insulation failed. Therefore use faucets prisoners, the which have specialproperties of the prisoner That minuscule voltage and largecurrent. Reduction process takes place once the prisonersQuickly During the overvoltage reaches its peakprice.Overvoltages in this case resulted in a drastic decline thanthe prisoners, so That the voltage current is limited despite the bigfall.

LA Voltage-Current Characteristics

If the maximum tension was more exhausted and live a normal voltage, current incarceration rose again so that the aftershocks are limited to approximately 50 A. Subsequent flow was finally turned off by the fire broke at the time The system voltage reaches the first zero point so that the tool acts as a valve that closes the flow; from here didapatkan name faucets prisoners. In the current arrester outages aftershocks large enough (200-300 A) is done with the help of a magnetic field. In this case, then both the amplitude and duration of follow-up current can be reduced and pemadamamannya system can be carried out before the voltage reaches zero price.

Aftershocks can be added that the current does not alwayshappen every time arresters work, depending on the presence or absence during overvoltage. This is understandable because the current apat aftershocks that just put out on the first zero currentor the previous one.

Based on its quality, known three arresters: substation (stationtype), the transmission line (line type) and distribution(distribution type) type substation kontruksinya heavier,karakteristinya better, higher current carrying capacity of its release (no more than 100 kA, 5 x 10 μs) and used to protect thesubstation and power transformers. This type of transmissionchannel is used to protect distribution transformers, transformer-powered small, and sometimes also a small substation. This type of distribution is primarily used to protect distribution transformers mounted on poles. Types trasnmisi and distributioncapacity are both made to withstand 65 kA with 5 x 10 μs waveform.

In the normal voltage conditions, fire bulkhead prevents anycurrent flowing into the column. In the event of an overload, insulation fire will die and disposed of to ground pressure. 50 Hzcurrents that appear later are limited by the endurance blockvalve and the sparks that arise will be cooled at room sparks.Sparks will quickly extinguished and then be ready to protect thearrester equipment wire from the pressure of the next voltage.Blanking period is very short, rarely able to last more than afraction of a millisecond.

Arrester that allows us to reduce the BIL requirements of the devices installed at the substation. On HV and EHV systems, reducing the BIL will reduce the cost of the devices installed. picture below shows a lightning arrester installed at substation 150 kV and 500 kV.

Ligtning Arrester (LA)

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The purpose of the arrester is to limit over-voltages that can appear on the transformer and other electrical devices either due to lightning or other electrical pressure. Base of the top of thearrester is connected to wires or terminals that must beprotected, and the base of the bottom connected to the ground.

Arrester insulation coordination is key in an electric powersystem. When the lightning came into the substation, arresterswork release electric charge (discharge), as well as reducing the voltage to be abnormal about the equipment in the substation.After a lightning arrester is released through, the current is stillflowing because of the system voltage; currents are calleddynamic or current flow aftershocks. Arresters must havesufficient resilience against the flow of energy from theseaftershocks, and should be able to decide, if at the time ofrelease arresters, voltage and current dynamic system is toohigh, then the arrester it may not be able to decide the flow ofaftershocks.

Requirements to be met by the arresters are as follows:1. Voltage spark (sparkover voltage) and the release voltage (discharge voltage), ie the voltage at the terminal at the time of the release should be quite low, so as to secure the insulating equipment. Spark voltage is also called the drain voltage between (gap breakdown voltage). Discharge voltage is also called residual stress (residual voltage) or IR voltage drop.2. Arresters should be able to decide the flow dynamics and can work continues as before. Limits of voltage current system in which the termination of these aftershocks are still possible, called the base voltage (rated voltage) of the arrester

Basic Impulse Level (BIL)

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     How is the reaction of materials to the impulse voltageinsulation? An examination showed that the ability to withstandincreased when the voltage that flows take place in periods of very rapid. To illustrate, we will conduct testing on the transformerinsolasi, using 50 Hz sinusoidal voltage between the windings tothe tank. Along with increasing voltage, it will reach a point where the voltage will drop. We assume That point with 46 kV (RMS) or 65 kV peak.
     If now we use dc impulses between the windings to the ground, we find that it takes twice the peak voltage (or 130 kV) before isolation of the breakdown (broken). The same thinghappened on suspension insulators, bushings, etc., unless the ratio between the impulse voltage and ac voltage peak close to1.5.
     For standardization, and to facilitate comparisons betweenthe same tool in restraining impulses, standards organizationshave determined the shape and peak value of the impulse wave.

Voltage Standard curve Impluls The equipment used todetermine the BIL

Picture above shows the standard impulse wave. The wavereached its peak after 1.2 μs and decreased to half of its peak at 50 μs. Peak voltage has a series of values ranging from 30 kV to 2400 kV (see Table)

Voltage Peak To test BIL 1.2 x 50 μs

Peak voltage is used to determine the quality of basicimpulse insulation (BIL) of a device. So, some devices(transformers, insulators, capacitors, resistors, bushings, etc.)that can withstand 1.2 x 50 μs waveform of 900 kV, is considered to have the quality of basic impulse insulation (BIL) of 900 kV.

Lightning antidote and Wire Transmission

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Lightning antidote to the House

Lightning rod consists of a simple metal bars that are on higher ground than the building, which connects the lightning towards the ground electrode by means of the connecting wire. This tool is able to prevent high current passing through the building, which could result in fire, or endanger the occupants. Lightning can be very dangerous; when lightning release, this tool can create a very high voltage between the conductors to the ground.

Lightning rod that is more modern electrical devices used on the system. This tool will divert lightning and move the high-voltage current into the ground before damage to the electrical device.

Thunderstorms and Wire Transmission

When lightning directly on the wire transmission, which contain a large electrical currents, then there will be a voltage in a very large number of wire to the ground. Dielectric strength of air will overflow and pass flashover. Wire will heal by itself and the exc

ess voltage will disappear in less than 5 μs.

However, the sparks generated by the lightning current will produce a high ionization between the wires and the ground, which works like a short circuit. Consequently teagnagn normal alternating current will flow back and forth followed by a large ionized flow. Flows like this will not dampen the sparks until the circuit breaker to open at the bas

e end of the wire. Circuit breakers will flow fastest in 1 / 60 second, which is equivalent to 16,000 μs after lightning struck the wire.

Lightning strikes directly on the wire transmission is rare, most often, the lightning will grab the ground wire that protects the transmission wire. In the latter case, the local current is still flowing on the wire, which produces very high local stress. Concentrated flow will be divided into two waves moving in opposite directions near the speed of light (300 m / μs). High voltage is an impulse wave that emerged from point to another, between the wire and ground Peak voltage (refer to the crest of a wave) can force one / two million volts. Ab gathered in front of the wave range of 300 m, while the tail bc several kilometers.

Waves that represent the point value per point of the current flowing in the wire. Most wire air, the ratio between surge voltage and surge current equivalent of about 400 Ω resistance. Voltage of 800,000 volts of pressure at some point will be followed by the current pressure on the 800.000/400 = 2,000 A.

During the wave goes through the wire, and I2R losses in the corona gradually come down, and followed by a drop in peak voltage.

When the wave reaches the insulator, the insulator will experience a large excess voltage. This period of rest is the voltage equivalent to the time it took the wave to reach the insulator. Voltage rises from its nominal value to hundreds of kilo-volt in 1 μs, corresponding to the wavelength of the front ab. If the insulator is not able to withstand the excess voltage, the flashover occurs, and generate currents that drive next-breaker will cause the circuit to work. On the other hand, if the insulation resistance, the wave will continue to run along the wire until it finally reached the substation. And this wave of impulse will result in damage.

Winding transformers, condensers, reactors and others, will be severely damaged if the experience flashover to ground. The cost of expensive repairs and even total destruction would make such a device can not function anymore. Excess stress can cause damage to the circuit breakers, separators, insulators, relay and others, which is a substation devices. To reduce the impulse voltage on the substation, lighting arresters (LA) is installed on all the wires that go into substation.

LA is designed to prevent the peak voltage that exceeds a certain level, such as 150 kV. Instead, the device in the substation is designed to resist the impulse voltage is higher than the lightning rod, such as 650 kV. Thus, if the voltage of 1000 kV substations into, LA it will divert most of the energy that comes into the ground. Residual impulse wave passing through LA would have the strength of 150 kV. The device is designed substation 650 kV impulse withstand.

lightning and electrical energy

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Clap

During the rainy season, through a fairly complicated process, charge separation occurs within a cloud, so that the positive charges move to the top of the cloud while negative charge stays below

Such transfer will cause an electric field inside the cloud. In addition, the negative charge at the base of the clouds refused to free electrons that exist underneath. As a result, the T becomes positively charged, due to induction. It will be formed an electric field and other potential between the cloud base and earth. So, appears an electric field between the electrons are repelled from the region T, with a positive charge at the top of the cloud.

The more positive charge that moves upward, the electric field under a cloud becomes stronger. This goes on until it reaches a critical level of ionization of air which begin to break down.Ionization occurs as the first time on the top roof of a building or tree tops, and sometimes appear as bluish light.

When the electric field is strong enough, lightning will immediately grabbed from cloud to earth. A lightning strike consists of a charge transfer from 0.2 to 20 coulombs, with the potential / voltage differential reaches hundreds of millions of volts. The speed of each stroke peaked around one or two microseconds and then drops by half within 40 μs. What is usually seen as a lightning strike, actually consists of several strike that followed each other in a very rapid timeframe. Total time release can last for 200 ms. The release also occurred between the positive with a negative flow in the cloud, rather than between the cloud base and ground. Thunder sounds generated supersonic wave riding. Lightning is caused by expansion of air around the lightning seized.

understanding electricity

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Electricity is the nature of the objects that emerge from the existence of electric charge. Electricity, can also be interpreted as follows:

- Electricity is the condition of certain subatomic particles, likeelectrons and protons, which led to the withdrawal and rejection ofstyles in between.

- Electricity is a source of energy that is channeled through wires.Electrical currents arising from electric charge flowing frompositive to negative channel channel.

Together with magnetism, electricity form the fundamentalinteraction known as electromagnetism. Electricity allows the occurrence of many well-known physical phenomena, such aslightning, electric fields and electric currents. Electricity use is common in industrial applications such as electronics and electric power.