# Electrical Measurements Questions and Answers – Ratios of Instrument Transformers

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

1. Transformation ratio of an instrument is defined as ____________
a) ratio of primary to secondary phasor
b) ratio of secondary to primary phasor
c) reciprocal of the primary phasor
d) reciprocal of the secondary phasor

Explanation: For an instrument transformer, the transformation ratio is defined as the ratio of the magnitude of the actual primary phasor to the magnitude of the secondary phasor.

2. For a C.T. the transformation ratio is given by which of the following relation?
a) R = $$\frac{I_s}{I_p}$$
b) R = $$\frac{I_p}{I_s}$$
c) R = $$\frac{1}{I_p}$$
d) R = Ip

Explanation: In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.
R = $$\frac{I_p}{I_s}$$
where, R is the transformation ratio
Ip is the actual primary winding current
Is is the actual secondary winding current.

3. For a P.T. the transformation ratio is given by which of the following relation?
a) R = $$\frac{V_s}{V_p}$$
b) R = $$\frac{1}{V_s}$$
c) R = $$\frac{V_p}{V_s}$$
d) R = Vp

Explanation: In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.
R = $$\frac{V_p}{V_s}$$
where, R is the transformation ratio
Vp is the actual primary winding voltage
Vs is the actual secondary winding voltage.

4. Nominal ratio of an instrument transformer is defined as the __________
a) reciprocal of the rated primary value
b) ratio of rated secondary value to primary value
c) reciprocal of the rated secondary value
d) ratio of rated primary value to secondary value

Explanation: In an instrument transformer, nominal ratio is defined as the ratio of the rated primary current or voltage to the rated secondary winding current or voltage.

5. For a C.T. the nominal ratio is given by which of the following relation?
a) Kn = $$\frac{I_{p(rated)}}{I_{s(rated)}}$$
b) Kn = $$\frac{I_{s(rated)}}{I_{p(rated)}}$$
c) Kn = $$\frac{1}{I_{s(rated)}}$$
d) Kn = Ip(rated)

Explanation: In a current transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary current to the magnitude of the actual secondary current.
Kn = $$\frac{I_{p(rated)}}{I_{s(rated)}}$$
where, R is the transformation ratio
Ip(rated) is the rated primary winding current
Is(rated) is the rated secondary winding current.
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6. For a P.T. the nominal ratio is given by which of the following relation?
a) Kn = $$\frac{V_{s(rated)}}{V_{p(rated)}}$$
b) Kn = $$\frac{V_{p(rated)}}{V_{s(rated)}}$$
c) Kn = $$\frac{1}{V_{s(rated)}}$$
d) Kn = Vp(rated)

Explanation: In a potential transformer, the transformation ratio is given by the ratio of the magnitude of the actual primary voltage to the magnitude of the actual secondary voltage.

where, R is the transformation ratio
Vp(rated) is the rated primary winding voltage
Vs(rated) is the rated secondary winding voltage.

7. Ratio correction factor is defined as _________
a) reciprocal of nominal ratio
b) ratio of nominal ratio to transformation ratio
c) ratio of transformation ratio to nominal ratio
d) reciprocal of transformation ratio

Explanation: The ratio correction factor for an instrument transformer is defined as the ratio of the transformation ratio to the nominal ratio.
R.C.F = RKn
where,
R.C.F is the ratio correction factor
R is the transformation ratio
Kn is the nominal ratio.

8. For a C.T. the turns ratio is defined as the _________
a) n = NpNs
b) n = 1Np
c) n = Ns
d) n = NsNp

Explanation: For a current transformer, the turns ratio is defined as the ratio of the number of turns in the secondary winding to the number of turns in the primary winding.
n = NsNp
where, n is the turns ratio
Ns is the secondary turns
Np is the primary turns.

9. For a P.T. the turns ratio is defined as the _________
a) n = NpNs
b) n = 1Np
c) n = Ns
d) n = NsNp

Explanation: For a potential transformer, the turns ratio is defined as the ratio of the number of turns in the primary winding to the number of turns in the secondary winding.
n = NpNs
where, n is the turns ratio
Np is the primary turns
Ns is the secondary turns.

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