Power Transformers

One of the important and commonly used transformers is the power transformer. It is widely used to step up and step down voltages at the electrical power generating station and distribution station respectively.

Why do we use Power Transformers in the Electrical Power System?

There are many reasons for using a power transformer in electrical power systems. But one of the most important reasons for using power transformers is to reduce power loss during power transmission.

Let us see how power loss is reduced considerably by a power transformer:

The equation of the power loss is given by:

P = I2 R

In the equation, I is the current through the conductor and R is the resistance of the conductor.

From the equation, we can conclude that the power loss is directly proportional to the square of the current flowing through the conductor. Hence, lower the magnitude of the current flowing through the conductor lesser the power loss.

To better understand the above theory, let us consider the following example:

  • Consider an initial voltage of 100 V and a load current of 5 A and the delivered power to be 500 W. In this case, the transmission line has to carry a current of magnitude 5 A from the source to the load. If we step up the voltage to 1000 V at the initial stage then the transmission lines only have to carry a current of 0.5 A to deliver the same power of 500 watt.
  • The voltage is stepped up at the start of the transmission line using a power transformer and the voltage is stepped down using another power transformer at the end of the transmission line.
  • This setup allows the reduction of the magnitude of the current to be traveled over a distance of 100+ kilometers drastically.

Construction of Power Transformers

The power transformer design, types, and accessories are dependent upon its size, application, and location. Following are the basic parts needed for the construction of power transformers:

  • Steel Tank (Body)
  • Core
  • Coil Winding
  • Conservator
  • Breather
  • Thermometer
  • Vent Pipe
  • Valves
  • Buchholz Relay
  • Tap Changing Switch

Features of Power Transformer

Rated Power 3 MVA to 200 MVA
Typical Primary Voltages 11, 22, 33, 66, 90, 132, 220 kV
Typical Secondary Voltages 3.3, 6.6, 11, 33, 66, 132 kV
Phases Single or three-phase transformers
Rated Frequency 50 or 60 Hz
Cooling Type Oil Forced Air Forced Cooling
Installations Outdoor or Indoor
Tapping On-load or off-load tap changers

Applications of Power Transformer

  • Power transformers used in electric power generation and distribution
  • Used for reducing power losses during electric power transmission
  • They are preferred in cases where the load is required to run at full capacity 24×7.
  • It is used in high voltage step-up and step-down.


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