Electrical Measurements & Measuring Instruments Multiple Choice Questions 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
Answer: a
Clarification: 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
Answer: b
Clarification: 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
Answer: c
Clarification: 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
Answer: d
Clarification: 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)
Answer: a
Clarification: 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.
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)
Answer: b
Clarification: 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.
