Electrical Engineering and Technology

Corte por láser para piezas en aluminio o metal

2018-03-20T05:05:00.002-07:00

El corte por láser es una técnica empleada para cortar piezas basado en un láser como fuente de energía. Esta técnica está basada en la alta potencia de la onda láser que se encuentra concentrada en un diámetro pequeño a través de un lente al momento de ser disparado. Cuando el láser hace contacto con la superficie, la misma se funde permitiendo el corte del material con la silueta deseada y gran precisión.

En la siguiente imagen se ilustran las partes de un cortador láser

Las aplicaciones del corte por láser son múltiples en una gran variedad de sectores, principalmente en procesos de manufactura; por ejemplo, en el sector industrial en motores, maquinarias y construcciones, en el sector aéreo y espacial; y el sector que ha tenido un auge en los últimos años el sector de mercadeo, publicidad, diseño de artes, iluminación, decoración y muebles.

En el siguiente video se muestra el proceso de corte por láser para una chapa de metal

Arte

Industria Automotriz

Decoración

Moda

Todos estos usos del corte por láser son posibles ya que las máquinas cortadoras por láser funcionan a través del Control Numérico Computarizado (también conocido por sus siglas CNC), las cuales son programadas con el diseño o figura deseada y posteriormente el cortador láser procede a realizar su trabajo.

Los beneficios del corte por láser son evidentes en la creación de diseños con infinidad de formas geométricas y siluetas, sin la necesidad del uso de plantillas, logrando acabados de primera en las piezas con bordes finos, lisos y limpios. Las ventajas más relevantes desde el punto de vista práctico son los siguientes:

Acabados: Fabricación de copias exactas en toda la producción, sin errores. Eliminación de sobrecostos por limpiar “residuos de material” que quedan al final del corte en otras técnicas
Variedad de materiales: Efectividad de corte en una gran cantidad de materiales como: cerámica, madera, plástico, goma y en un gran número de metales.
Versatilidad: Posibilidad de fabricación de piezas simples o estructuras mucho más complejas en una sola pieza. Una sola máquina de corte por láser puede sacar adelante el trabajo de varias máquinas con otras tecnologías.
Programación CNC: Lo que implica un gran ahorro de tiempo, aumento de la precisión y una disminución de los errores.
La tasa de accidentes es mínima: Al haber una mínima intervención humana en el proceso, los accidentes laborales disminuyen.

A diferencia de los procesos tradicionales de corte de materiales, el corte por láser garantiza la calidad de los resultados, con una alta rentabilidad y rapidez al elaborar piezas en cantidades masivas; además que este tipo de técnica no genera residuos tóxicos o agresivos con el ambiente.

En otro orden de ideas, existe otra técnica para modelar metales, conocida como el plegado de metales Esta técnica implica el uso de una prensa, la cual está conformada por una herramienta superior, conocida como el punzón, y una herramienta inferior, llamada matriz. La prensa controla el movimiento de ambas herramientas, y suministra la fuerza por medio de servomotores eléctricos o bombas hidráulicas. El ángulo de plegado es determinado por la profundidad de penetración del punzón dentro de la matriz.

LASER MECAFORT es una empresa especialista en corte por láser y plegado de metales con más de 17 años de experiencia en el mercado. Cuentan con una capacidad de producción que sobrepasa los 10 millones de piezas de corte por láser anuales; esto gracias al uso de tecnología de primera y el trabajo en conjunto con marcas como TRUMPF y AMADA, las cuales son líderes en el mercado mundial de alta gama y venta de maquinaria laser y plegadoras.

La tecnología láser TRUMPF incluye sistemas para el corte, marcado y tratamiento de superficies y componentes tanto bidimensionales como tridimensionales. La compañía cuenta con láseres de CO2 de alto rendimiento, láseres de diodo, láseres de marcaje, láseres de soldadura, ofreciendo resultados de alta calidad y precisión.

Para el plegado de metales LASER MECAFORT opera con maquinaria japonesa de alta gama marca AMADA. La característica principal de esta maquinaria es su alto rendimiento, ya que permite programar y sacar desarrollos con precisión exacta previo a elaboración de la pieza. Esta tecnología permite instalar múltiples estaciones de trabajo en las cuales la maquinaria es configurada una sola vez para realizar variedad de plegados.

LASER MECAFORT realiza trabajos en cualquier tipo de metales y ofrece diversidad de espesores para los cortes por láser: en acero al carbono de 0,5 a 25 mm, acero inoxidable de 0,5 a 20 mm, aluminio de 0,5 a 12mm, latón de 0,5 a 10 mm, y cobre de 0,5 a 8 mm. En cuanto al plegado de metales, LASER MECAFORT cuenta con punzones con ángulos desde 85 a 30 grados, una gama que va desde punzones rectos hasta patas de cabra para jugar con las pestañas a necesidad del plano; poseen matrices mono V con altura de 120 mm, con lo que ofrecen de hasta 30 grados o aplastado.

Redacción: Ing. Gabriela Figueroa

Edición: Ing. Aaron Paradas

Industrial peristaltic pumps: discover how they work

2018-03-20T04:47:00.000-07:00

The needs of the industrial sector cause the use of almost all types of industrial pumps, with certain preferences in applications that need bombs of positive displacement, such us, the employment of industrial peristaltic pumps.

Industrial peristaltic pumps, how they work?

The industrial peristaltic pumps are a certain type of positive displacement pump which can be used for pumping a wide variety of fluids, move and push liquids and solids. This form of positive displacement pump is based on alternating compression and relaxation of the tube or tube, then drawing the contents back in the tube or hose.

The design of a peristaltic pump consists of a flexible tube embedded inside a circular cover that is inside the pump. The operation of the pumps is simple; while the rotor rotates the part of the tube closes the fluid in a way that forces it to move through the tube.

Once the cycle ends, the tube opens again to start again after the action of the cam.

We can say that industrial peristaltic pumps work like our intestines. Due to the fact that the pump doesn´t contaminate or touch the product to be pumped, industrial peristaltic pumps are used to pump harsh liquids since they don´t damage the pump. They are also capable of pumping out minerals and corrosive gases.

In theory, a peristaltic pump would be ideal if it has an infinite diameter of the head and the largest possible diameter between the rollers. The problem with this pump is that, in practice, its manufacture is not possible. Therefore, a manufacturer of peristaltic pumps must approach the parameters of an ideal peristaltic pump capable of providing a constant flow and free of pulsations due to the unlimited life of the pump.

Although it is ideal for dispensing beverages, for food manufacturing or pharmaceutical production, it is advisable to consult the manufacturer of peristaltic pumps to see if it is possible to use it in the pumping of wastewater, toxic sludge in mining or even for pumping machines in certain open heart surgical operations.

In those applications where the isolation of the product is essential, it is necessary to have industrial peristaltic pumps, such as handling of dry matter and solid particles.

Using industrial peristaltic pumps, characteristics, advantages, and applications

The internal characteristics of the hose carried by industrial peristaltic pumps make it possible to work in extreme conditions. The good thing is that the hoses can be removed and put easily in a matter of minutes. The elastomeric hoses are suitable for the handling of sensitive, toxic and viscous products such as sludge, gases, and oil.

The flexibility of the hoses allows a symmetrical design that reduces backflow and makes it fully reversible. A manufacturer of self-supporting peristaltic pumps will equip these machines with hoses prepared to pump all kinds of liquids (very liquid or cut sauces, products with solids or particles in suspension), fluids and products.

The flexibility of the hoses allows a symmetrical design that reduces backflow and makes it fully reversible. A peristaltic pumps manufacturer will equip these machines with hoses prepared to pump all kinds of liquids (very liquid or cut sauces, products with solids or particles in suspension), fluids and products.

Choosing an incorrect pump or hose can damage the solid fraction or cause spillage of the product inside the pump. The good thing about industrial peristaltic pumps is that they are very well isolated, have no mechanical seal, require little maintenance and are capable of pumping fluids with dry matter such as sludge, sludge, slurry, organic waste, and glycerine.

REFUND POLICY FOR PAYONEER

2017-01-05T06:08:00.001-08:00

Payment Refund Policy

The entire amount will be refunded if I can’t manage schedules after accepting a project.

I accept payment by milestones, there will be no refund for milestones completed (as agreed by the client).

If I can not finish the project within deadline, the client can ask for refund of the current milestone and they can end the contract

Variable frequency driver – Engineer and Installation 1/#

2016-02-29T11:24:00.000-08:00

Nowadays, using variable frequency drivers is the most common way to control AC motor´s speed in industries worldwide, looking to avoid DC motors in the system and therefore eliminated the maintenance of the brushes and the expensive control systems.

Once it’s decided to install a VFD in the process whichever it might be, developing engineering for its proper installation is need, and the following article highlights some of the factors that have to be considered.

In first place is important to have in mind during the engineering process that the installation can be one of the two following:

1. The VFD will be installed with a motor that has been design to run with a VFD. The article will focus on this option.

2. The VFD will be installed with an old motor that used to run without speed control, and it was not design to work with a VFD. Considerations in this case will be analyzed in an up-coming article.

For the first case New Motor – New VFD, the following points shall be taken under consideration:

1. Location of the VFD.

2. Distance from VFD to Motor (total wiring route).

3. Type of cable from the VFD to the motor.

4. Kind of wiring installation.

5. Installation of control wiring.

6. Electrical protection against short-circuits and terminal overload.

7. Harmonics generated by the VFD.

8. Effects of reflected waves.

9. High frequency Foucault currents between the motor and the pump or compressor.

10. VFD autonomy when faults in the main power feeder.

1. Location of the VFD.

A VFD is an electrical equipment with electronic components that generate a lot of heat, therefore it has to be notice that the VFD should have internal fans to help the refrigeration, the environmental conditions play a key factor in the engendering process for this matter.

2. Distance from the VFD to the Motor.

The distance in this case is no relate to the voltage drop that it produces, it is suppose that the cable has been selected accordingly to this considering the distance and the installation type. In this case is important to be aware of the distance in order to eliminate any reflections in the tension wave, which may be present as a result of long distances between VFD and Motor. The distance from the VFD and the motor (wiring distance) should be always informed to the manufacture, depending on the technology used, filters may be needed in the arrangement.

3. Cable used to feed the motor

There are several literatures regarding this matter, at the same time some manufactures design cables to be used exclusively with from the VFD to the motor and is one of the most expensive items in the project.

The cable that goes from the CCM to the VFD can be a regular cable. The cable that goes from the VFD to the motor have to be special for the application, further analysis on this subject will be presented.

Control the AC motor speed using a VFD is something that has become more frequent over time. Let’s reason the cable design more suitable to avoid the troubles that come with it, the manufactures usually present this information to the client but sometimes are not considered as a result of negligence or ignorance of the actual problem.

4. Power Cable Wiring

The cable should be installed apart from other feeders of the system. Different VFD cables to motors can be installed in the same route. It is recommended that the cable from the CCM to the VFD, VFD to Motor and control cables are installed separately.

It’s important to avoid that the cable to the motor goes parallel to other cables for long distances, this to avoid electromagnetic interferences produce by changes in the voltage at the VFD.

If the control cables and the power cables have to crus at certain point, be sure that they do it with an angle of 90 degrees from each other.

The air way trays shall have a good electrical connection between them and respect the grounding system. It’s recommended to use aluminum air ways to level the potential more efficiently

5. Selection and routing of control cables

Similar to the power cables they should go through separated routes.

All control cable shall be shield.

Shall be used a twisted par with double shield cable for analog signals. This kind of cable is also recommended for the signals of the pulse generator. Use an individual pair for each signal. Do not use a combined return for different analog signals.

The best alternative for low voltage digital signals is a cable with double shield, but a several cables with simple shield can also be used.

Analog and digital signals should be transmitted through separated shield cables.

The signals controlled by a relay can be transmitted through the same cable used for digital entries, as long as the voltage is less than 48 V. It is recommended that the signals controlled by relay are transmitted using a twisted pair cable.

24 V DC and 115/230 V AC signals never have to combine in the same cable.

See it in Spanish

E.g. Enrique Paradas

Basics Of Motor Starters And Contactors - Repost

2015-12-17T11:56:00.000-08:00

Welcome to this EATON’s guide, which is about starters, devices that control the use of electrical power to equipment, usually a motor. As the name implies, starters “start” motors. They can also stop them, reverse them, accelerate them, and protect them.

Starters are made from two building blocks, contactors and overload protection:

Contactors control the electric current to the motor. Their function is to repeatedly establish and interrupt an electrical power circuit.
Overload Protection protects motors from drawing too much current and overheating, from literally “burning out.

The Contactors

A contactor can stand on its own as a power control device, or as part of a starter. Contactors are used in applications ranging from the light switch to the most complex, automated industrial equipment.

Contactors are used by electrical equipment that isfrequently turned off and on (opening and closing the circuit), such as lights, heaters, and motors.

Whatever the application, the function of the contactor is always the same: to make and break all power supply lines running to a load. Or, as defined by NEMA, to repeatedly establish and interrupt an electrical power circuit.

We’ll start by talking about the building blocks of a starter: the contactor and overload protection. We will then conclude with a discussion on starters.

Here are the topics that we will cover:

The Contactor (magnetic contactor, how the contactor operates, contact life etc.)
Overload Protection (How motors work, what is an overload?, overload relay, tripping etc.)
The Starter (magnetic motor starter, starter circuitry, types, standards and ratings etc.)
Helping the Customer (NEMA or IEC?, checking the motor nameplate etc.)

Download

http://electrical-engineering-portal.com/res/Basics-of-Motor-Starters-and-Contactors.pdf

Transfer Switch Application and Selection Manual - Repost

2015-11-23T03:53:00.000-08:00

This Manual is intended to provide guidance in the selection and application of transfer switch equipment in a variety of power generation situations. Transfer equipment is available in many configurations, all sharing the same basic function, that of providing a means to connect electrical loads to either of two independent power sources.

Download:
http://electrical-engineering-portal.com/download-center/books-and-guides/power-substations/transfer-switch-selection

How Loud Is a Wind Turbine

2015-07-30T04:55:00.001-07:00

Electrical Installation Guide 2015 - FREE Download Now

2015-07-27T07:12:00.000-07:00

Designer, Consultant, Contractor, Panel builder, Facility manager, Student, teacher, Standardisation or certification experts. we all have to know and comply to electrical installation standards and regulations, in order to ensure the safety (and more and more the energy efficiency) of our customers' electrical installations.

These international standards, set by the IEC, are complex and keep evolving; as a result, we struggled to stay informed.

As an example, are you aware that the IEC 60364 "Low-voltage electrical installations" part 4-42 "Protection for safety - Protection against thermal effects" has been updated in 2014, and that in particular it now includes recommendations for arc fault protection?
- in premises with sleeping accommodations;
- in locations with risks of fire due to the nature of processed or stored materials
[...]
In a.c. circuits, the use of arc fault detection devices (AFDDs) in compliance with IEC 62606 will satisfy the above-mentioned recommendation."

The technology also evolves, which may impact the way we design installations: as an example, LED lighting is increasing its share very fast, and as you know the LED lamps electrical characteristics and behavior (at startup in particular) require special care to be taken when choosing the related control and protection devices. And there is nothing worse than a customer site where the lighting circuit breakers may trip, or where the contactors may face welding of contacts, requiring urgent and costly on-site intervention.

Fortunately, experts in the field from Schneider Electric got together in order to update the Electrical Installation Guide (EIG), a free and complete guide about electrical installations and the related standards.

Edited since several dozen years, it is a reference work which helps you understand and comply to the IEC standards to be applied in 2015. Thanks to this free and simplified guide, you'll ensure the reliability of your commercial, industrial, or domestic electrical installations.

What's new or updated in 2015 edition of the Electrical Installation Guide?
An updated list of relevant IEC standards, new content about LED lighting, new content about Arc Fault Detection Devices (AFDD), some updated chapters about "connection to the MV utility distribution network" and "MV and LV architecture selection guide for buildings", and also some updated examples of Energy Management architectures.

The content of the Electrical Installation Guide (2015 version) is clear and practical; there's no other guide of that stature!

The paper version costs 60€ but we propose you to DOWNLOAD the EIG 2015 right NOW and FOR FREE by clicking on the button below:

DOWNLOAD GUIDE HERE

How does a Transformer work ?

2015-07-23T18:32:00.002-07:00

I will be uploading from now on material that I find explain electrical principles in the easiest understanding way so my readers find it all in just one place.

Hope you learn something once again.

Buchholz Protection for Transformers

2015-07-23T18:15:00.000-07:00

The Buchholz protection, protects the transformer again every abnormal phenomenon produce inside the tank. It bases in the fact that the irregularities in the transformer functioning cause heating in the winding and in consequence the production of gases from the oil, the quantity and speed of its production increases at the time the damage spreads.

The gases that are produce inside the tank go up through the tube in which the relay is installed and they get trap in it.

Disposition of the relay is shown in the scheme 2. The relay box is filed with oil and it contains the floats a1 and a2. When ever little gas bubbles are produce, this elevate from the transformers tank to the oil tank and get trap in the relay, in it the level of oil drops progressively. The top float inclines and when the amount of gases is sufficient, it causes contacts c1 to close and activated the alarm circuit.

In the cases that no measure is taken given the alarm or given the failure the amount of gases is high, the second float drops closing a2 causing the main transformer circuit breaker to open. If a electrical arc is produce inside the transformer, a violent flow of gases will go to the oil tank and c2 to will close suddenly preventing important damage to the transformer.

Over the top of the relay is a faucet b1, that allows gasses to scape. another faucet b2, allows to prove that the floats and contacts are in good shape.

The relay detects shorcircuits between windings, core and core - windings, phase interruption, excessive overload, oil leak etc. The great advantage of this relay is its high sensibility to warn deterioration or incipient faults, when the most sensibly protection systems wont be that effective.

The characteristic of the gases trp in the Buchholz relay can give an idea of the type of defect and where it produced. The most simple verification is the combustibility test of the gas. In case of electric arc the oil decomposes producing acetylene that is flammable.

The color of the gases can give an idea of the nature of the defect.

White: Paper destruction.
Yellow: Wood destruction.
Black or Grey: Oil decomposition.
Red: Winding isolation damage.

A peephole allows to see the gases, the color have to be seen minutes apart from the moment of the event.

Why AC Power Systems have 3 phases?

2015-07-22T19:56:00.000-07:00

I am kind of in a wondering phase right know, it all began with the frequencies and then... this next question WHY 3 PHASES. May be more than one electricity enthusiast that haven't got deep in to it but now is wondering. It is mostly mathematics the explanation, by increasing the number of phases the amount of power that is transmitted gets to a point that it is just not efficient, it gets to complex and expensive.

Lets hear this Senior Transmission Engineer for a moment, he does why I like the most... get complex subjects explained in the most simple way possible.

Hope you learn something new once again.

Any subjection for topics... leave it in the comment section.

Basic Principles Generators/Motors AC 2/2

2015-07-20T16:01:00.000-07:00

Lets see now what this people have to say about AC machines.

Once again, hope you learn something new.

Basic Principles Generators/Motors DC 1/2

2015-07-20T05:12:00.000-07:00

Taking it back once more, back when I was at the university starting to know the electrical machines I have to be honest I had nightmares trying to acknowledge all the laws of physics that rule the way machines worked.

Today I just now thing, that the simpler the better so for those that just wanna know how it works and don't get to much over there heads here is a video that puts it just in simple words the way everyone likes it. Its an all video but I thing it is just great piece of work of explanation,

Hope you enjoy it and learn one or tow things.

If any suggestions for future post live it in the comment sections. Remember getting things explained in the easiest way is what I intend to do.

Watch the second part of this post: Basic Principles Generators/Motors AC 2/2

Motor Selection Guide

2015-07-17T15:03:00.000-07:00

When it comes to a Selection of an Electrical Motor for a set application some times engineers find themselves in a bast range of options and got confuse on which are the best "technically" for that option.

Once the engineers makes up their mind now they have to establish the rated characteristics to order the motor to the given manufacturer. Lets face it it is not that easy to remember all this parameters.

A few years ago when I was a fresh engineers coming out from the university I had a hard time selecting and ordering motors for a project I was involved in, and back then i found this Motor Selection Guide made by General Motor.

The guide basically describes all the characteristics that a motor has or could have if they are required and help you to properly choose and order the motor you really need. If by any chance you order a motor and its not the correct there comes the troubles so better take your time getting to know about types of motors is what I recommend.

So here is the link where you can find the guide I talk about. Hope you find it Useful.

DOWNLOAD MOTOR SELECTION GUIDE

The origin of electrical frequencies – Why 50 or 60 Hz

2015-07-17T13:48:00.000-07:00

A couple months ago I decided to emigrate from my home country Venezuela, to the southern country Chile. As an electrical engineer while I was looking for a job I spend some of my free time on studying the local electrical system, the first factor that I have to get used to is that here the system works at 50 Hz and most of the equipment are specify according to the IEC Standard. For the last 8 years I had worked on 60 Hz systems and using mostly ANSI Standard, it is not a BIG deal just have to get used to it.

While studying the electrical system and white all the spare time I started wondering, seriously, WHY? are there two frequencies and so close to each other, true be told never gave much thoughts to the subject always think of that like, its always been like that, obviously there is a story behind. While doing my research I found this article that explain very well the reasons. It was made originally on Spanish so it translate it as precise possible.

The origin of electrical frequencies – Why 50 or 60 Hz

Even when today it seems that there is always been a unique frequency for electrical power transportation, on each of the main zones of influence: 50 Hz for Europe and 60 Hz for EEUU, it haven't been like that. Will do a look back through the history of the frequencies that have been used.

In 1891, Westinghouse engineers, in Pittsburgh, took the final decision of considering 60 Hz as the frequency for the future, that same year, the engineers of Allgemeine Elektrizitats Gesellschaft (AEG) choose 50 Hz.

Since those decisions were taken, those frequencies became the "frequencies for alternative current transmission" standard, in fact this decision keeps affecting us nowadays. The frequency generally depends on each country, one of the most peculiar cases is Japan, when a person travels from Tokio to Osaka have to keep in mind that has come from a 50 Hz to a 60 Hz zone.

With this little review will try to clarify the reasons why the engineers of Westinghouse and AEG didn't agree on an unique frequency and why they choose a different value.

To know the background of the decisions that set the frequencies of our days we have to go back by the end of the XIX century, for that we need to go through the documents that allows us see the traces of these decisions and this will let us chronologically review the facts that lead them.

Since early times the electric energy wasn't used as an amusement, it was used as a safe method to light the houses, the boulevards or as a method of energizing electrical motors in factories to produce mechanical movement that will allow us discard the expensive and little efficient mechanic transmission systems: through axis, belts, pulleys, and gears that were used in the industrial revolution Era. The used frequencies have changed from 40 and 53 Hz in Europe, and 133 + 1/3 and 125 Hz in EEUU to 50 and 60 Hz respectively. This article wont cover the transitions period from direct current, promoted by Edison and Kelvin and the alternative current (1887), whose defender was Nikola Tesla. That was a true war, technologically, economically and politically wise.

1866 - 1890

Even when it seems incredible in those days each manufacturer, Edison, Thomson - Houston, Westinghouse, Siemens, etc. generated, produced and distributed electrical energy, also they manufactured the motors and lamps that will work it. Where the electricity did not develop to the fullest as a conglomerate and it was attend to be used as individual items one from another, an important technological delay took place like in England, France or Spain.

As a clear example of this situation, in 1878, Edison Machine Works manufactured dynamos, Edison Tube Company manufactured conductors, Edison Lamp Works manufactured lamps and Electric Illuminating Company of New Yorl generated electricity in the Pearl Street Central.

Focusing in AC, by 1884, Dr. Hopkinson demonstrated the possibility of the transmission of AC over short distances, while in that same year Gibbs and Gaulard presented the second version of their called 'Secondary Generator' precursor of the transformer, in the Turin exhibition. Tests were made of transmission from Turin to Lazio. The primary network was around 40 km long, 20 kW and 2.000 V. In this period, Max Deri, Otto Blathy and Karl Zipernowsky, noticing the defects of Gibbs and Gaulard's machine, improve it closing the magnetic circuit. On September 16th of 1884 was finally completed the installation the transformer, called like that the first time, it characteristics were 120/72 V, 1.400 VA and 40 Hz.

In 1886, Westinghouse bought the transformer patents design by Gibbs-Gaulard and Max Deri, Otto Bláthy and Karl Zipernowsky and with the work of Stanley developed an ironclad transformer used in their Great Barrington exhibition, it was feed from an generator of the kind made by Siemens. It had poles, worked at 1.000 rpm therefore the 133+1/3 Hz.

f (p * n) / 120

Where:

f = frequency en Hz

p = number of poles

n = spin speed in rpm

In change other manufacturers like Thomson-Houston Company used alternators of 15.000 cicles (p*n), that permitted a frequency of 125 Hz

For this reazon it began in EE.UU the "High Frequency Era" in the generation and transmission of electrical energy. Westinghouse 133 +1/3, Thomson y Houston 125 Hz y Fort Wayne Jenny Electric 140 Hz.

Really, in those years, the main use of electricity was lightning and either frequency perfectly fulfilled the requirements of quality, with lower frequencies the lamps would began to produce an annoying flashing effect.

1890 - 1925

This a period in the one appears an element that will annoy the relative tranquility of manufacturers, the induction motor.

The motors that were used for the development of mechanical power that moved the machines tools were couple directly, motor - machine toll, of the the machine worked at 80 rpm, it will required a 200 poles motor working ar 133 +1/3 Hz. This problem, the elevated pole number, wouldn't appear in Europe since there they used 40 Hz, therefore they required only 60 poles machines.

In 1890, AEG and Oerlikon used 40 Hz for their 175 km three-phase electrical line, from Frankfurt (receptors) to Laufen (production) using an alternator of 50 V phase tension, 32 poles with a spin speed of 150 rpm, that gives 40 Hz frequency. The transmission was made transforming in the origin from 50 to 8.500 V and in Frankfurt it was reduce to 65 V. Later they realize the stroboscopic problems, due the low frequency applied to the lamps and by 1891 they chose to used 50 Hz, that solve both problems. Generators design to feed the motors and lightning systems.

In 1890, the engineers form Westinghouse realize that working with frequencies above 130 Hz was preventing their induction motor development, to many poles in the machines stator. Analyzing the problem, came with the conclusion that 7.200 cicles (p*n), and therefore 60 Hz, was the optimum value for their motors and the coupling of the machines that were manufactured back them.

Steinmetz just before started working at Thomson-Houston Company determined the resonance problems, with the material that Hartford Electric adquied, was due the harmonics of the 125 Hz signal used to supply the energy. The way to solve this was reducing to 62,5 Hz. General Electric kept using 50 Hz that used its European partner AEG. In 1894, General Electric, realize that they where loosing sales in the AC market and drastically change to 60 Hz.

Is wasn't unanimity respect the 60 Hz, one of the biggest projects of the generation in the times, The Niagara Falls project, in 1892, to give electrical energy to Chicago chose a two-phase alternator of 12 poles, rotating at 250 rpm, that gives 25 Hz, Westinghouse was the company that develop the project. Like ways other manufacturers in those times build alternators of 8.000 cicles - 66 +2/3 Hz.

1925 - Actuality

Even when it seems like since 1921 every electrical system in EE.UU used 60 Hz, it wasn't like that. The transformation process to the standard frequency last until 1948. For example the Mili Creek Installations were not modified until the end of WWII.

In England it was even worse since the Electric Light Act came up, where is was stated that every electrical material that were manufacture had to be able to be used for any person or compay, this prevent the transformer develop by Gibbs and Gaulard to be used in England (this was one of the reasons of their technological delay) this was different in EE.UU or Germany.

A extremely peculiar case is Japan. The Yokohama department sent to EE.UU. engineers so they can study the different technologies about the electricity in the moment, 1889. When they came back to Japan, they were convince of the pros of the "high frequency" and bought and installed an alternator from Stanley-Kelly-Chesney (SKC) that worked at 133 + 1/3 Hz, in Keage Canal. In 1895 sold an alternator of 50 Hz to a company in Tokyo.

Lets Remember that Stanley of SKC then change to General Electric, and was then that determined that 133 +1/3 was to high frequency for AC electrical motor, and changed the alternator production so they generated AC at 60 Hz. When a company of Osaka bought an alternator to AGE, this one manufactured them to generated at 60 Hz and there the frequency division in Japan began to the momment: East 50 Hz and West 60 Hz.

Summary

Truly, the determination of the most convenient frequency came from the necessity (like all technology existing) of over come the tech problems that were presenting while the electrical energy spread around the world.

So, in the first years the electrical energy was used almost exclusively for public lightning, hotels, banks and houses of wealthy people and to avoid the stroboscopic effects high frequencies were used.

When the electrical energy got into the fabrication process and the energy consume was designated no only to lightning, but also to power in motors the frequency was reduce to the the actual values.

The reason WHY 50 Hz in Europe and 60 HZ in EE.UU, came only and excusably determined for the position of preponderance of AEG in Europe and GE in EE.UU, whose engineers at some point chose chose on of the actual frecuencies

"The winner sets and tells the history"

Source: Articulo “El origen de los 50-60 Hz en la transmisión de la energía eléctrica”. Wrote by Eduardo Aznar Colino y Joaquín Royo García, and publish in Técnica Industrial 242 (Septiembre de 2001). Vía afinidadelectrica.com.ar

Translated by: Eg. Aaron Paradas

Lightning Protection Systems Design - Part II

2013-06-28T16:03:00.000-07:00

In the first part of this article we saw how a lightning forms and its principal characteristics, current and duration, also we saw the different criteria that are used to protect our installations. Today I will talk a little be more about this methods and how we can represent in a drawing the protection zones.
One thing that I forget to mention in the previous part is that the methods that I mentioned are used in installations of “Low Voltage” or under 69 kV since the Standard IEEE 998. It means that the conic and sphere method are useful when we are talking about houses, industrial installations and any kind of infrastructure that is not a high voltage substation.
Let’s focus in the rolling sphere method, where there are different radiuses according to standard IEC 62305. There are many formulas to determine the radio of the sphere but the ICE uses the following equation:

Where:
r: radius of the sphere.
I: Current in kA that will have the lightning when it first hits.
We will obtain a table where it shows for zones of levels of protections:

	L1	L2	L3	L4
Minimum Current [kA]	3	5	10	16
Probability of the current will be higher than the minimum [%]	99	97	91	84
Rolling Sphere Radio [m]	20	30	45	60

From this we can deduce that higher the current, bigger will be the radio of the sphere and therefore more space can be establish between lightning rods, ironically the problem presents with the smaller currents around 3 kA, the radio of the sphere is only 20 m and it will require more lightning rods to protect the structure.
The probability that the current of the lightning overcome the minimum current gives us a warranty that in fact the protection zone described by the selected radio will work perfectly for currents higher than the used for the design; the radius that shall be used for those currents will be larger and the protection zone in that matter will be wider. For example the strictest (level 1) establishes that only 1% of the lightning could be lest that 3 kA, it is a quiet secure statement, as it is for probability.
I recommend that you read the “Lightning Protection Handbook” of Erico, there you will find further explication about that topic.
Lightning Protection Zone Drawing
Now let’s get to the best part… How do we represent the protection zone in a AUTOCAD drawing?
First of all I thing we shall see how it is NOT done.
1) Indicated the resulting radio for the protection zone: for example if our protection level is 2, the sphere radio will be 30m, if we see a plan view, is shall NOT be simply be represented as circle of that radio with the lightning in the center given that this will be a error.
Note: the counties of measure are given in mm

Plan view – mistaken zone

What is inside the red circle should be the protection zone but there is the problem…. Lightning rods high haven’t being considered. In the following figure can be seen that for a lighting that is 15m tall (green post) and with spheres of 30 m of radio (in red) the protection zone is define is represented and it should be done in a different way, I mean, a circle is drawn centered in the lightning but the radio will be defined by the on which the sphere touches the grown.

Side view of the protection zone.

In this case is 25,98m, establishing the zone as is shown in the figure bellow, in green hatch.

Side view of the define protection zone.

Finally in the figure shown bellow we can see how the protection zone really is view from above.

Side and Plan View of the protection zone.

Even when apparently it is correct there is a detail with the plan view representation, it doesn’t indicate the high of the protection zone in particular, for example: if our house were closer to the border of the protection zone Ii will be out of it but seeing it from above won’t be notice. Watch the next figure.

Side and Plan View; structure outside the protection zone.

What we should do then is indicated the guaranteed high of the protection zone for the structures, ex: our house is 4,5 m tall, then we should find a new radio, this is done geometrically finding the point where the form of the sphere (in red) separates from the grown exactly 4,5m (yellow line).

Side view to determine the new protection zone radio.

We have now a new radio of 10,18m
Now the protection Is defined in the plan view for 4,5 m heights.

Side and Plan View. Structure outside the zone.

Now it is seen that the house is outside the zone and it is not protected.

With this we get to the final of this part, in the next post you will learn how to draw the zones of mutual influence between two or more lightning rods.

You can download the file DWG of the example Here.
Hope you liked it,
Go to Spanish Post

EDX, Take Great Courses from the World´s Best Universities

2013-06-03T20:47:00.001-07:00

In my eternal research to improve my knowledge with great quality material and reducing the costs leads by it, it has been brought to me the education program EDX, program that personally consider a great initiative, now as it at the was introduce to me, I will present to you the distance educational program EDX.
EDX is an initiative from the most recognized universities worldwide, which presents the possibility, to be part of courses through the internet with specialized professors in the subjects and all these in all matters is FREE.
The way everything works is very simple; all you need to do made a FREE Registration to the program and to do so the only requirement is and active email account. Once you register you just have to sing up to a course of your choice which in its description will have the start date and all you need to know about it.
CERTIFICATION, Each course that is available, presents a series of activities or assignations that seek to establish a way to test the fixation of the knowledge on the student. Having finished the course and mate successfully all the assignations established, the institution responsible of the course will gift the student a certificated with the suffix “X” at the end of the institution name, example HARVARDX, MITX (it is not a joke this universities and much others are in this program).
INSTITUTIONS, now the best part, the institutions in charge of the program and development of courses, the logos of all the institutions and universities with a great reputation worldwide, remember it is free education from teachers of these universities. Clicking the logo you could see the courses that each university presents in EDX program.

Technorati Tags: EDX,US Universities,MIT,Hardvard,Berkeley,Free Courses,Education

Lightning Protection Systems Design - Part I

2013-03-06T20:17:00.001-08:00

One of the most esoteric topics among electrical engineers is the Lightning Protection Systems, more specific lightning rods, as I have already mentioned lightings are a very complex natural phenomenon therefore is it difficult to establish and unified criteria, for this reason is that there exists a lot of opinions and strange myths that brings as result wrong lightning protection designs.
Before going any further I must confess that I am no expert in the subject, I have design a few Lightning rods using “the traditional criteria” that I´ve found in earlier documents, however I found necessary to develop a research about basic concepts. This is the results of it.
The lightning
Air is not a perfect isolating media, given that its dielectric resistance is around 30kV/cm, when a potential difference is reach between tow electrical conductor points a spark will occur inevitably (Family size, the one we call Lightning)
Depending of the polarization, the lightings are classified on negatives (electrons or negative charge ions) or positives (positive charged ions), according to its origin (Fig. 1) there are inside lightning (inside the cloud), intercloud (from cloud to cloud), clout – earth lightning (80% percent of the lightning produced and therefore the most important to us) and at last earth to cloud lightning.

Fig1. Types of lightning
Despite the short duration that they have (microseconds), lightnings have a huge destructive potential given that they carry current around 30 kA typically, up to 300 kA have been register, therefore the necessity of protecting installations and ourselves.
Lightning Formation
The lightning (this point forward it will be considered as and cloud to earth and negative) is produced by the union of the ion leaders (Fig. 2) the ascendant - Up Streamer and the descendent – Stepped Leader, they precisely are the ones that make a ionize row which is used by the lightning to go through (Fig. 3). The lightning produces when the ion leaders touch each other as seen in Fig. 4.

Fig. 2 Ascendant and Descendent Leaders

Fig. 3 – Ionize Row for by the ascendant and descendent Leaders

Fig 4. Lightning Formed
When a Lightning takes place it drains the negative charge of the cloud, it can occur a several times in a row, that why sometimes it looks like blinking in the sky.

Lightning Engineering Data

Parameter	Magnitude
First discharge amplitude	Avg. value: 30 kA, only 10% supers 75 kA
Subsequent discharge amplitude	Avg. value: 8 kA, value of the 10% - 30 kA.
Increase rate of the first discharge current	Avg. value: 7kA/us, value of the 10% 13 kA/us
Increase rate of the subsequent discharge current	Avg. value: 25 kA/us, value of the 10% 80 kA/us
Discharges by lightning	25% of the lightnings have 4 discharges, the biggest have least than 18
First discharge load	Avg. value: 6C, valor del 10% of 30C.

Protection against Atmospheric Discharges
Given that a lightning is a natural phenomenon and as one it is unpredictable, it is impossible to avoid its incidence on the structures or people 100% of the times, what a protection system does is attract the lightning that otherwise will strike in an undesired area.
The most costumed way to do so is by using lightning rods, the simplest system consist on a captor element of cooper or one with and equivalent resistance, connected solid to earth trough a isolated download wire.

The all idea is that the lightning rod has a location so it represents functions as an descendent leaders attraction element, setting it above any other structure according the location criteria.
Lightning Rod Location Criteria
Basically there are two methods to realize lightning systems designs, define the location and the amount of the lightning rods; there are the cone protection and the sphere method.
Cone Method
This method consists in setting a cone around the lightning rod and then assuming that the structures and area inside de cone will be protected.
NFPA 780 indicates two types of angles, for structures bellow 7,6m would be considered a 63 degrees angle (2 to 1 relation), for structures above 15 m would be considered a 45 degrees angle.
The next figure shows a zone considering a 45 degrees angle.

A 3D view, shows the cone formation

Applying transparency to the cone let us see the house and the person of reference.

This method is considered obsolete and lacking of scientific basement, several books consulted agree with this consideration and recommend using and electro-geometrical methods.
Rolling Sphere Method
This method derives from the call electro-geometric model (EGM); it predicts that considering an imaginary sphere of determinate radium, the lightning will have a bigger probability to strike the structures or objects that are inside of the sphere area or touch its surface, staying protected everything that it’s in the outside.
The fist reference for this method comes from the work done by Ralph H. Lee in 1997.

When the sphere is roll around the lightning rod it forms and inverted funnel as shows de next figure.

Seen in 3D.

Applying transparency it let us see the house and the reference person, inside the funnel formed by the protection zone.

The protection zone have a limited range, therefore a portion of the equipment or structure might been left unprotected.

The house on the right side is no longer been protected as it should, to overcome this problem it have to be installed another pole with a lightning rod on the top of it.

Now as we see in the figure above the house on the right side is protected by the new lightning rod, both zones overlap and forms a bigger protection zone.

Seen in 3D we have our new protection zone.

But there is an additional subject to consider, when the sphere roll between and around the two lightning rods, it creates a bigger zone than the addition of them as is shows in the figure below.

Resulting in something more likely to a circus tent.

Design considerations
According to the book: Lightning protection for engineers at the time of the calculation of the resulting protection zone it must be considered the following:
Cone Method:
1. It is a method based in a theoretical approximation and as there is been said, the lightning in most cases wont behave as it is predicted to.
2. The concept applied for this method does NOT implied safety for people since touch voltages may affect them.
3. The angle of protection is in relation to the structures high.
Rolling Sphere Method:
1. It is a method based in a theoretical approximation and as there is been said, the lightning in most cases wont behave as it is predicted to.
2. The concept applied for this method does NOT implied safety for people since touch voltages may affect them.
3. The radium of the sphere depends of the standard that have been considered:
· (US) NFPA 780, R=46m
· (US) Dept Energy and Deot Defense, R=33m

Technorati Tags: Lightning Protection Electricity Lightning Rod NFPA 780

· IEC 62305: Level I, R= 20 m / Level II, R=30m / Level III, R=45m / Level IV, R=60m
· BS 66551 (Brithis) R=20m
See the post in Spanish

Standards that apply to the subject:
· NFPA 780 - 2011
· IEEE Std. 998-1996. IEEE Guide for Direct Lightning
Stoke Shielding of Substations
· US Air ForceAFI 32-1065Grounding Systems (2003)
· US Air Force 91-201US Air Force Explosives Safety (2001)
· US Army385-64, Chapter 12Ammunition & Explosive Safety Standards – Lightning
· US NavyNAVSEA OP5Chapter 6, Lightning Warning and Protection (1999)
· US MilitaryMIL-STD188-124Grounding, Bonding and Shielding for Common Long Haul/Tactical Communications Systems (1992)
· US MilitaryMIL-HDBK 419A Grounding Bonding and Shielding for Electronic Equipment and Facilities (Volume I, Basic Theory, 1987)(Vol. I)
· US MilitaryMIL-HDBK 419A Grounding Bonding and Shielding for Electronic Equipment and Facilities (Volume II, Applications, 1987)(Vol. II)
· DOEM440.1-1 Department of Energy Electrical Storms and Lightning ProtectionDOEDOE/EH-0530Department of Energy Lightning Safety (1996)
· DDESBDDESB 6055.9Department of Defense Chapter 7, Lightning Protection (1997)FAAFAA-STD-019deLightning Protection, Grounding, Bonding and Shielding Requirements for Facilities (2002)
· FAAFAA 6950.19APractices & Procedures for Lightning Protection, Grounding, Bonding and Shielding Implementation (1996)
· NASA E0012EStandard for Facility Grounding and Lightning Protection (2001)
· National Weather Service30-4105Lightning Protection, Grounding, Bonding, Shielding and Surge Protection Requirements (2004)
· APIAPI-2003American Petroleum Institute Protection Against Ignitions Arising out of Static, Lightning, and Stray Currents (2008)
· British StandardBS6651Protection of Structures against Lightning (1992)
· Indian StandardIS2309Protection of Buildings and Allied Structures Against Lightning - Code of Practice (1989)(in English)
· Polish StandardPN86Lightning Protection of Structures(in Polish)7th
· AS/1768Australian Code, Lightning Protection (2004)
· Chinese Code GB50057-94Design Code for Lightning Protection of Structures(in English)
· Russian CodeRD 34.21.122-87Design Code for Buildings and Structures

In the part 2 it will be show how to draw the protection zones using AUTOCAD

Tips for Specifying A.C Motors to work in Hazardous Classifying Areas

2013-03-01T06:45:00.001-08:00

It is a fact that The National Electrical Code, as well as the international standards establishes the general characteristics and specifications to be done at the time of developing an A. C. motor specification (also see Motor Selection Guide), it is common that engineers only identify the rated values that usually appears on characteristics motors data, but turns up that motors that will be used in classify areas as oil and petrochemical industries standards dictated that they must have two identification – rated values plaques, the first with the rated operational values:
Speed, Voltage, Power Factor, efficiency, Full load current, service factor, frame, etc. as in the following picture

The other plaque brings very important data that experience have thought me must people do not mention any of this at the time of purchase a motor and then when the order arrive comes along with regrets since the motor can’t be used; the other plaque indicates the type of area that it have been made to work in.
Class, Division, work group. (E.g. Class 1, Division II Groups ABCD)
Protection Type IP.
Temperature class (It’s not the same that operation temperature of the motor), this is referred to the type of gas in the atmosphere that it’s around the pump – motor package.
Start Type: DOL (Direct on-line, soft – starter, VFD - Variable Frequency Drive)

All this parameters al highly important for the specification of an A.C motor as well as the general rated values, and are this characteristics the ones that will make more or less expensive the motor but the cannot be omitted. Therefore that if your to specify the replacement of a motor that have suffer damage of as well if it’s the case that is for a new installation, Care and attention its needed when the rated values and plaques data it’s been indicated in the purchase order.

The most important specifycation to be made in A.C. motors in this cases is class temperature, now lets see what it is.

Temperature class: The maximum superficial temperature of and equipment or in this case an electrical motor can not reach the ignition temperature of the atmosphere potentially explosive that it is in. This ignition temperature it’s determined in labs, and it’s considered as the lowest temperature of the equipment case, where the inflammable substance that surrounds it begins to blaze in presence of air. The characteristics of the Gases that are in the area under normal condition and non desired condition as well shall be known in order to determine the ignition point. Once it is calculated the following table is used to specify the motor, and this specification must appear on the motor rated plaque.

Temperature Class	Maximum superficial temperature	Ignition Point of the combustible material
T 1	450 ^oC	> 450 ^oC
T 2	300 ^oC	> 300 ^oC
T 3	200 ^oC	> 200 ^oC
T 4	135 ^oC	> 135 ^oC
T 5	100 ^oC	> 100 ^oC
T 6	85 ^oC	> 85 ^oC

See Spanish Post

Standards that apply to the subject:

IEC – International commission electrotechnical

60079-10-1, 60079-10-2, 60079-10-2, 60079-10-2

NFPA – National Fire Protection Association

30, 45, 496, 497, 499

NEMA – National Electrical Manufactures Association

250

PDVSA - Petróleos de Venezuela S.A.

N – 252, 90619.1.101

API – American Petroleum Institute

RP 500, RP 505

ANSI – American National Standards Institute

12.01.01, 12.10, 12.12.01