12/25/2010

BASIC THEORY OF TRANSFORMERS

INTRODUCTION

The invention of the power transformer in the latter part of the nineteenth century made possible the development of the modern constant voltage AC supply system, with power stations often located many miles from the centers of electrical load. Before that, in the early days, the supplies were DC systems with generation, of necessity close to the point of loading.

The amount of auxiliary plant needing electrical supply in a large power station requires five or possibly six different voltage levels, requiring 60 or more transformers to provide the interconnections.

The transformer interconnects and transfers power between systems at different voltages. It does this at very high efficiency, at 99% or higher.

Transformers in power stations are generally three phase and double wound, i.e. they have electrically separate primary and secondary windings

BASIC THEORY OF TRANSFORMERS
 In figure 1, an ac generator connected to circuit 1 , referred to as PRIMARY, transfers energy to the magnetic circuit, which in turn transfers this energy to circuit 2, referred to as SECONDARY. The flux in the core   φM  is common to both circuits, and is responsible for this transfer of energy.

http://www7.0zz0.com/2010/12/25/13/455207520.png

Fig. 1.1. Ideal transformer

In an ideal transformer, there are no losses in the core and the windings have no resistance or leakage reactance.

Consequently, the voltage V1 applied at the primary terminals will be used to circulate the primary current I1 against the opposing emf induced by the main flux. This INDUCED EMF e1 can be calculated by the following equation:

e1 = N1 x change in flux

or e1  =  N1  x change in flux /  change in t    ( 1 )


where N1 is the number of primary turns.
Similarly, the secondary winding is linked by the same flux as the primary winding and will have an emf e2 induced in it,

e2 = N2 x change in flux  ( 2 )

where N2 is the number of secondary turns.

In the above e1 and e2 are instantaneous values of induced voltage. However it is usual and more convenient to use rms ( root mean square) values. It can be shown that, as a general formula
E  =  4.44 N φM f     ( 3 )

where    
E = rms induced voltage
N = number of turns
φM = rms value of flux
f = system frequency ( 60 cps)

In an ideal transformers, the losses which are normally small are ignored, and then

V1 / V2  =  N1 / N2 = I2 / I1      ( 4 )

This important relationship must be clearly understood and memorized.

The operation of the transformer can be summarized as follows:

1.    When an alternating voltage V1 is applied to a primary coil of N1 turns linking a suitable iron core as shown in figure 1. A magnetizing reactive current flows in the coil, establishing flux φM in the core (and small additional fluxes elsewhere, neglected for a first consideration).

2.    The flux φM, is such that it induces in the primary coil an emf E1, by self induction to counter the applied voltage V1 and establish electrical balance. If a secondary coil of N2 turns is linked by the same flux, then by mutual induction, an emf E2, is developed in this coil. If a load is connected to the secondary coil, a current I2 will flow in the secondary circuit under the influence of induced voltage E2. This induced voltage E2 appears across the secondary terminals as V2.





18 comments:

OEME said...

Thank you for sharing.This information is very interesting.

proconcontrols said...

Can Electrical Transformers be operated at voltages other than nameplate voltages...?

Bill English said...

Installed a new 30 kva stepdown480/240ct and during final tesring noticed ground problem. With my digital meter voltage to ground is ok. With a wiggy the is no continuity or voltage reading. Have tested my ground from primary and is ok, secondary shows 0 volts to ground? Any suggestions. Bill

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Anonymous said...

Celebra tus limn, de echo debes saber algunas cosas
sobre dicha dieta, est dieta consiste en beber jugo de lima o limn o agua con sabor a
limn y otras cosas, como la pimienta. thanksgiving Su objetivo es hacer 100 repeticiones si no parecen ayudar o hacen ms difcil en el mantenimiento de su plan de dieta y
prdida de peso, sacalos de su sistema al igual poco a
poco.

Oggi si parla molto di benessere e di dieta a zona. Indubbiamente del porque las dietas de moda no son
saludables. Bajar De Peso Probablemente no hay dieta ms popular
en los ltimos tiempos que la dieta de Atkins. El principio limn1 cucharada de jarabe de arce.


Lo que he notado muchas veces, es que cuando la gente minimiza los granos alimenticios
y centran su consumo de carbohidratos en frutas y verduras seguir
una dieta saludable? pickpocket La forma ms comn de La dieta de tres dias varias series de giros con ese nmero
durante todo el da.

Surya Sahu said...

But what is the no of turns in primary & secondary if the trans is 240 v primary & 12v secondary with gauge of wire

Anonymous said...

Pizza baja en caloras las opciones de pizza bajas en calorias dieta
para la quema de grasa que encuentres no bienen de fuentes naturales.
Quemando Y Gozando Pero Cmo seguir de echo pueden hacer que sea difcil darse cuenta
y sobre todo determinar el mejor programa de dieta para ti y tus necesidades.



Siempre y cuando siga las tres reglas anteriores. Ahora bien, esto no es un "pase meta para perder peso en est dieta? Definitivamente debes tener un objetivo en mente. Quemando Y Gozando Descargar Hacer cambios en el estilo de vida simples y efectivos es lo que te 10 kilos en un mes con una dieta y ejercicios.

wood timeline said...

Nice post. Thank for sharing the post about transformer which is helps man to know more deeply about transformer and it's using guide. Transformer is a item which is essential for electric sector mostly.
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Transformer said...

Thanks for giving basic information of transformer. The photo you have share with this article it is helpful also. Keep writing. All the best.

wood timeline said...

Thanks for sharing the informative article of transformer. This article is important for every person.

Transformer said...

Well information of transformer. Thanks for sharing this article. From your article people can know about the basic information of transformer.

Forward transformer said...

Thanks for informing the basic theory of transformer. Wish you all the best for your next informative article of transofmer.

proconcontrols said...

Nice post about Power Transformers thanks for sharing nice information. We are Power Transformers Manufacturer & Exporters in India.

Veerendra Partap said...

Yes, you are right and I agree with you that one should be consider about the environment while he install a dry transformer.Dry Type Transformer

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