What is transformer | uses of transformer | Types of transformer | Working principle of transformer | Transformer parts | Construction of transformer or Transformer Diagram.
INTRODUCTION
One of the main reasons of adopting a.c. system instead of d.c. system for generation, transmission and distribution of electric power is that alternating voltage can be increased or decreased conveniently by means of a transformer. In fact, for economical reasons, electric power is required to be transmitted at high voltages whereas it has to be utilised at low voltages from safety point of view. This increase in voltage for transmission and decrease in voltage for utilisation can only be achieved by using transformer.
Q. What is a transformer ? What is its necessity in the power system ?
Or, Explain the working principle of a transformer.
Or, State why the core of a transformer is laminated ?
Ans. :- Transformer : A transformer is a static device which transfers a.c. electrical power from one circuit to the other at the same frequency but the voltage level is changed usually as shown in fig. (a). When the voltage is raised on the output side (V, > V,), the transformer is called a step-up transformer, whereas the transformer in which the voltage is lowered on the output side (V, <V,) is called a step-down transformer.
Necessity : In our country, usually electrical power is generated at 11 kV. For economical reasons, a.c. power is transmitted at very high voltages (220 kV or 400 kV) over long distances, therefore, a step up transformer is applied at the generating station. Then to feed different areas, voltages is steeped down to different levels (for economical reasons) by transformer at various substations. Ultimately for utiļisation of electrical power, the voltage is stepped down to 400/230 V for safety reasons.
Thus, transformer plays an important role in the power system. The pictorial view of a power transformer is shown in fig. (b). The important assessories are labelled on it.
Working Principle of a Transformer:-
The basic principle of transformer is electromagnetic induction.
A simple form of a transformer is shown in fig. It essentially consists of two separate windings placed over the laminated silicon steel core. The winding to which a.c. supply is connected is called primary winding and the winding to which load is connected is called a secondary winding.
When a.c. supply of voltage V, is connected to primary winding, an alternating flux is set up in the core. This alternating flux when links with the secondary winding, an e.m.f. is induced in it called mutually induced e.m.f. The direction of this induced e.m.f. is opposite to the applied voltage V, according to Lenz’s laws as shown in fig.
The same alternating flux also links with the primary winding and produces self induced e.m.f. E. This induced e.m.f. E, also acts in opposite direction to the applied voltage V, according to Lenz’s law.
Although, there is no electrical connection between primary and secondary winding but electrical power is transferred from primary circuit to the secondary circuit through mutual flux.
The induced e.m.f. in the primary and secondary winding depends upon the rate of change of flux linkages. The rate of change of flux (d fie/dt) is the same for both primary and secondary. Therefore, the induced emf. in primary is proportional to number of turns of the primary winding (E 1 is proportional to N1) and in secondary is proportional to number of turns of the secondary winding (E2 proportional to E1).
:. In case, N2 > N1, the transformer is step-up transformer and when N2<N1, the transformer is step-down transformer.
Turn ratio :- The ratio of primary to secondary turns is called turn ratio, i.e., turn ratio = N1/N2.
Transformation ratio :- The ratio of secondary voltage to primary voltage is called voltage transformation ratio of the transformer. It is represented by K.
K=E2/E1 = N2 / N1
(since E2 is proportional to N2 and E1 is proportional to N1 ).
