# Electrical Measurements Questions and Answers – Differences between C.T. and P.T.

This set of Electrical Measurements Questions and Answers for Entrance exams focuses on “Differences between C.T. and P.T. “.

1. Potential transformers are used to measure _________
a) high voltages
b) low voltages
c) high currents
d) low currents

Explanation: Potential transformers are also known as P.T. and are used in the measurement of high magnitude of voltages.

2. Potential transformers are used with _________
a) high range voltmeter
b) low range voltmeter
c) intermediate range voltmeter
d) very high range voltmeter

Explanation: In general, potential transformers are used with low range voltmeters. They are also used for energizing the potential coils of low range energy meters and wattmeters.

3. Potential transformer is similar in design to a _________
a) C.T.
b) Step up transformer
c) Power transformer
d) Step down transformer

Explanation: In terms of design, the potential transformer resembles a power transformer. Potential transformers have a very low loading capacity of the order of a few volt amperes.

4. The secondary winding of a P.T. is designed for _________
a) 220 V
b) 2.2 kV
c) 1.1 kV
d) 110 V

Explanation: A potential transformer is generally used for the measurement of the very high magnitude of voltages in a circuit. But the secondary winding of a P.T. is designed for a capacity of 110 V.

5. The primary current in a C.T. is _________
a) independent of secondary circuit
b) dependent on the secondary circuit
c) depends on the transformation ratio
d) depends on the nominal ratio

Explanation: A C.T. is used for the measurement of high magnitude of currents in a circuit, while a P.T. is used for the measurement of high magnitude of voltages in a circuit. Primary current in a C.T. is independent of the secondary circuit conditions.

6. The excitation current of a C.T. _________
a) varies over a fixed range of operation
b) varies over a wide range of normal operation
c) is fixed over a range of operation
d) is fixed always

Explanation: In a potential transformer, the excitation current remains constant under normal operation. While in a current transformer, the excitation current varies over a wide range of operations.

7. Secondary of a P.T. can be open circuited.
a) True
b) False

Explanation: In a C.T., the secondary winding must never be open circuited when current is flowing in the primary winding. While in a P.T., the secondary winding can be open circuited without any damage to the circuit.

8. When C.T. is connected in series with a line, a large voltage exists across the primary.
a) True
b) False

Explanation: In a P.T., full voltage appears across the primary winding when it is connected across the line. While when a C.T. is connected in series with a line, a very small voltage appears across the primary winding.

Sanfoundry Global Education & Learning Series – Electrical Measurements.