Question

The transformation ratio of a transformer is 5. If the primary voltage of the transformer is 400 V, 50 Hz, the secondary voltage will be
A) 2000V, 250 Hz
B) 80 V, 50 Hz
C) 80 V, 10 Hz
D) 2000 V, 50 Hz

Answer 1

Hint The transformation ratio of a transformer gives us information about the ratio of the secondary voltage to the primary voltage. The frequency of the voltage remains unchanged in a transformer.
$\text{Transformation ratio = }{\displaystyle \frac{\text{secondary voltage}}{\text{primary voltage}}}$

Complete step by step answer
We’ve been given that the transformation ratio of a transformer is 5. Using the relation
$\Rightarrow \text{Transformation ratio = }{\displaystyle \frac{\text{secondary voltage}}{\text{primary voltage}}}$,
we know that the transformation ratio is 5 and the primary voltage is 400 V, so we can write
$\Rightarrow \text{5 = }{\displaystyle \frac{\text{secondary voltage}}{400}}$
Multiplying both sides by 400, we get
$\Rightarrow \text{secondary voltage}=2000V$
Now on getting transformed only the voltage changes but the frequency of the AC voltage that is being transformed will remain constant i.e. 50 Hz.
So, the secondary voltage will be 2000 V and the frequency will be 50 Hz which corresponds to option (D).

Additional Information
These are designed for measuring high voltage connected to the transmission and distribution systems. They are also used in electrical metering systems, electrical protection systems. Potential transformers step down the voltage of high magnitude to a lower voltage or a lower voltage to a higher magnitude so that they can be measured with standard measuring instruments. As a result, they should have a very low error margin so that the measurement is accurate. There are three main types of voltage transformers; capacitor voltage transformers, electromagnetic voltage transformers and optical voltage transformers.

Note
We should be careful in remembering that a transformer only changes the value of the potential and not its frequency. If we assume that the frequency also changes similar to voltage, we will obtain the answers corresponding to option (A) which will be wrong.