Power transformers are used for transmission & receiving purpose, whereas distribution transformers are used only for distribution purpose.
Power transformer voltage ratio varies b/w 756 kV to 11kV. Whereas the distribution transformer voltage ratio varies b/w 33kV to 430V.
Power transformers usually have higher MVA rating compare to distribution transformers.
To understand the above, I want you to understand the different voltage levels which we use from starting power generation until its distribution;
- Generally, electrical power is generated at low voltages i.e. 11kV. Large generators are designed to generate voltage ranging from 11 kV to 28 kV and frequency in 50 Hz or 60 Hz range. But to generate at 33kV, the size of the generator might be twice as large as the size of the 11kV generator.
- Now this generated energy is transmitted over the transmission lines of several hundred kilometers when a current flows through these wires some energy is lost as heat. The higher the current, the more heat is lost. Hence we need to transmit the power at low current to minimize the conductor size and losses. To reduce the current we need to increase the voltage. In transmission/generating stations we use Step-up transformer to increase the voltage to say 220 kV or above, these transformers are called as power transformers.
- Now this EHV transmission line terminates at the local receiving station, where 220 kV voltage is step down to say 33 or 11kV using the step-down transformers, these transformers are also called as Power transformers.
- Now, these 11kV voltage line is then distributed along every distribution station of the city, where the voltage is further step down to 430V AC using the step-down transformer. Transformers used here are called Distribution transformers.
- This 430V (3 Phase & 1 Neutral) AC is then given to industrial and household consumers. Normally household consumer gets 230V as a standard single phase voltage, this configuration is achieved with one phase and one neutral wire.
Above points can be visualized as follows;