# Electrical Measurements Questions and Answers – Characteristics of Potential Transformers

This set of Electrical Measurements & Measuring Instruments Multiple Choice Questions & Answers (MCQs) focuses on “Characteristics of Potential Transformers”.

1. Increasing secondary burden _____________
a) increases Is
b) decreases Is
c) keeps Is constant
d) decreases Ip

Explanation: When the secondary burden of a potential transformer increases, it leads to an increase in the secondary current. As a result the primary current also increases.

2. For a given Vp the Vs __________
a) increases
b) decreases
c) remains constant
d) depends on the supply

Explanation: For a particular value of primary voltage Vp, the value of the secondary voltage Vs decreases. This leads to a decrease in the actual ratio.

3. What is effect of the secondary burden on the ratio error?
a) ratio error is constant with secondary burden
b) ratio error decreases with secondary burden
c) ratio error increases with secondary burden
d) depends on the supply voltage

Explanation: As the secondary burden is increased, the ratio error also increases and becomes more negative. Ratio error varies linearly with respect to the change in the secondary burden.

4. Vp is leading in phase, while Vs is lagging in phase.
a) True
b) False

Explanation: As the secondary burden is increased, winding voltage drop increases. Voltage Vp is leading in phase while Vs is lagging in phase. As a result the phase angle increases with the secondary burden.

5. What is the effect of p.f. on secondary burden?
a) Ip shifts towards Io
b) Ip deviates from Io
c) Ip is independent of Io
d) Ip and Io cancel eachother

Explanation: When the power factor of the secondary burden is reduced, Ip shifts towards Io. Voltages Vp and Vs come closer to Ep and Es.
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6. How is the transformation ratio dependent on the secondary burden?
a) decreases
b) increases
c) remains constant
d) depends on the supply

Explanation: As the primary voltage Vp is constant, the induced primary e.m.f Ep is reduced. Similarly the secondary voltage Vs is reduced with respect to Es. As a result the transformation ratio increases.

7. Decrease in p.f. makes Vs to lead Vp.
a) True
b) False

Explanation: As the power factor is decreased, Vs leads in phase while Vp decreases in phase. Thus the phase angle reduces with the decrease in power factor (lagging).

8. At constant voltage how is frequency affected by flux?
a) decreases with an increase in flux
b) increases with a decrease in flux
c) remains constant
d) depends on the current

Explanation: When frequency is increased at a constant voltage, the flux decreases. Voltage ratio decreases as the magnetizing and iron loss components of current are reduced.

Sanfoundry Global Education & Learning Series – Electrical Measurements.