Question

At what voltage and frequency is the electric power generated at the power generating station?
A. 15kV, 50Hz
B. 11kV, 100Hz
C. 11kV, 50Hz
D. 11kV, 500Hz

Answer 1

Study the electric power distribution standards and norms followed in various countries. Explain the disadvantages of transmission of power at high voltages. Also, the frequency of supply affects the transmission.

Complete step by step answer:
We know that at the power generating station the power is usually generated at voltages 11kV, 22kV, 33kV or 66kV. These values were arbitrarily chosen in the past and have continued over the years. One plausible explanation we can give is that they could have been chosen to account for 10% losses encountered while transmission. Therefore, if we want 10 kV supply and if 10% would lose in the transmission we will get only 9 kV. We know that generating higher voltages is expensive. It can be made cost effective by generating a lower voltage and then using a step up transformer to increase the voltage step by step as needed. Hence, 11kV voltage is generated.

We know the supply frequency for the transmission is around 50Hz in Europe and India. Higher frequencies are not used as they increase the impedance of the transmission system. This reduces the power transfer capability and increases the system losses.

So, the correct answer is “Option C”.

Additional Information:
In some countries such as North America, the electric power is generated at 60Hz frequency.

Note:
The voltage supplied in residential areas is 240V; 50Hz. Students should note that some of the power generating stations also generate power at high voltages like 22 kV, 33 kV and 66 kV if it is to be transmitted to the long distance. But since the distance increases the resistance of wire also increases. This may increase the loss in the transmission.