Transformer basics

Transformers are one of the most important components of any power system. It basically
changes the level of voltages from one value to the other at constant frequency. Being a
static machine the efficiency of a transformer could be as high as 99%.
Big generating stations are located at hundreds or more km away from the load
center (where the power will be actually consumed). Long transmission lines carry the
power to the load centre from the generating stations. Generator is a rotating machines
and the level of voltage at which it generates power is limited to several kilo volts only
a typical value is 11 kV. To transmit large amount of power (several thousands of mega
watts) at this voltage level means large amount of current has to flow through the
transmission lines. The cross sectional area of the conductor of the lines accordingly
should be large. Hence cost involved in transmitting a given amount of power rises many
folds. Not only that, the transmission lines has their own resistances. This huge amount of
current will cause tremendous amount of power loss in the lines. This loss will
simply heat the lines and becomes a wasteful energy. In other words, efficiency of
transmission becomes poor and cost involved is high.
The above problems may addressed if we could transmit power at a very high
voltage say, at 200 kV or 400 kV or even higher at 800 kV. But as pointed out earlier, a
generator is incapable of generating voltage at these level due to its own practical
limitation. The solution to this problem is to use an appropriate step-up transformer at the
generating station to bring the transmission voltage level at the desired value where for simplicity single phase system is shown to understand the basic
idea. Obviously when power reaches the load centre, one has to step down the voltage to
suitable and safe values by using transformers. Thus transformers are an integral part in
any modern power system. Transformers are located in places called substations. In cities
or towns you must have noticed transformers are installed on poles – these are called pole
mounted distribution transformers. These type of transformers change voltage level
typically from 3-phase, 6 kV to 3-phase 440 V line to line.