Transformers and Power Transmission

Transformers and Power Transmission

Transformers are a very important component in present-day life as they make large power systems feasible. To efficiently transfer numerous megawatts of power across countries, very high line voltages are required– in the series of 161 to 1000 kV.

Nonetheless, the highest possible functional designed voltage for large generators is about 25 kV. The ideal transformer has the output power nearly equal to input power. While for an actual transformer, the output power is always less than input power due to power losses.

Power Transformation

The transformer has no internal moving components, and also it moves energy from one circuit to the other by electromagnetic induction. There may be external cooling which might consist of heat exchangers, radiators, fans, and oil pumps.

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Transformers are generally used because a change in voltage is required. Electrical power is transformed from its primary coil to the secondary coil due to changing flux.

Principle for Transmission


This relation describes that currents are inversely proportional to the respective voltage, therefore in a step-up transformer when Vs increases, current decreases. This is the principle that is used for the electrical supply network, where the transformer increases the voltage and reduces the current, so it can be transmitted over long distances.


Power losses in Transformer

The power losses in transformers are due to the following reasons:

  • Eddy Currents

The induced currents are setup due to changes in magnetic flux in the closed conducting loops. These currents are in a perpendicular direction to the flux so as to oppose the cause that produces them and is called eddy currents.

This problem can be reduced by using a laminated core between the lamination sheets. It will stop flowing eddy currents.

  • Hysteresis Loss
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This one is due to repeated and continuous magnetization and demagnetization of the core due to the flow of alternating current.

This problem can be solved by using a soft iron core in transformers.

Reduction in Power loss during Transmission

Generation of electrical power at low voltage is much cost-effective. Theoretically, this reduced voltage power can be sent to the receiving end. This low voltage if transmitted causes greater line current which without a doubt triggers even more power losses.

However, if the voltage of a power is increased, the current of the power is decreased which creates a decrease in ohmic or I2R losses in the system, reduction in the cross-sectional area of the conductor i.e., a decrease in capital cost of the system and also it also boosts the voltage regulation of the system.

Due to these, reduced power must be stepped up for reliable electrical power transmission. This is done by step-up transformer at the sending outside of the power system.

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As this high voltage power may not be dispersed to the consumers straight, this should be stepped down to the desired level at the receiving end with the help of a step-down transformer.