EEE RGIPT Amethi U D Dwivedi
Electrical Machine-I
Tutorial-2
Topics:
1. Polarity test of single-phase transformers
2. Equivalent circuit of a single-phase transformer
3. Referring the equivalent circuit parameters from one side to the other side of a transformer
(Assume sinusoidal steady-state operation and neglect losses unless stated otherwise.)
Q1. A single-phase transformer has 500 turns on the primary and 100 turns on the secondary.
During a polarity test, when the primary and secondary are connected in series aiding,
the measured voltage is 260 V. If the primary supply voltage is 240 V, determine the
secondary voltage and verify the polarity.
Q2. A 230/115 V single-phase transformer is subjected to a polarity test. The voltmeter
across the series-connected windings reads 345 V. Determine whether the transformer is
additive or subtractive and justify numerically.
Q3. The equivalent circuit parameters of a transformer referred to the primary side are: R1 =
2 Ω, X1 = 4 Ω, R2 = 0.5 Ω, X2 = 1 Ω. The turns ratio (N1/N2) is 2. Calculate the
equivalent resistance and reactance referred to the primary side.
Q4. A 5 kVA, 400/200 V transformer has the following parameters on the primary side: R1
= 1.2 Ω, X1 = 2.5 Ω, R2 = 0.3 Ω, X2 = 0.6 Ω. Find the equivalent circuit parameters
referred to the secondary side.
Q5. A transformer has an equivalent resistance of 3 Ω and equivalent reactance of 6 Ω when
referred to the primary side. If the turns ratio is 3:1, determine the equivalent resistance
and reactance referred to the secondary side.
Q6. The following parameters are obtained from tests on a single-phase transformer: R1 =
0.8 Ω, X1 = 1.6 Ω, R2 = 0.2 Ω, X2 = 0.4 Ω. The transformer ratio is 4:1. Calculate the
approximate equivalent impedance referred to the primary side.
Q7. During a polarity test on a 230/110 V transformer, the measured voltage across the
series combination is 120 V. If the primary is energized at 110 V, determine the
secondary induced voltage and state the polarity.
Q8. A 10 kVA, 250/125 V transformer has winding resistances R1 = 0.6 Ω and R2 = 0.15 Ω.
Find the total copper resistance referred to the low-voltage side.
Q9. The equivalent impedance of a transformer referred to the secondary side is (1 + j2) Ω.
If the turns ratio N1/N2 = 5, calculate the equivalent impedance referred to the primary
side.
Q10. A single-phase transformer has the following parameters referred to the primary side:
Req = 2 Ω and Xeq = 5 Ω. If the primary voltage is 400 V and rated current is 10 A,
calculate the approximate voltage drop in the transformer.
Electrical Machine-I
Tutorial-2
Topics:
1. Polarity test of single-phase transformers
2. Equivalent circuit of a single-phase transformer
3. Referring the equivalent circuit parameters from one side to the other side of a transformer
(Assume sinusoidal steady-state operation and neglect losses unless stated otherwise.)
Q1. A single-phase transformer has 500 turns on the primary and 100 turns on the secondary.
During a polarity test, when the primary and secondary are connected in series aiding,
the measured voltage is 260 V. If the primary supply voltage is 240 V, determine the
secondary voltage and verify the polarity.
Q2. A 230/115 V single-phase transformer is subjected to a polarity test. The voltmeter
across the series-connected windings reads 345 V. Determine whether the transformer is
additive or subtractive and justify numerically.
Q3. The equivalent circuit parameters of a transformer referred to the primary side are: R1 =
2 Ω, X1 = 4 Ω, R2 = 0.5 Ω, X2 = 1 Ω. The turns ratio (N1/N2) is 2. Calculate the
equivalent resistance and reactance referred to the primary side.
Q4. A 5 kVA, 400/200 V transformer has the following parameters on the primary side: R1
= 1.2 Ω, X1 = 2.5 Ω, R2 = 0.3 Ω, X2 = 0.6 Ω. Find the equivalent circuit parameters
referred to the secondary side.
Q5. A transformer has an equivalent resistance of 3 Ω and equivalent reactance of 6 Ω when
referred to the primary side. If the turns ratio is 3:1, determine the equivalent resistance
and reactance referred to the secondary side.
Q6. The following parameters are obtained from tests on a single-phase transformer: R1 =
0.8 Ω, X1 = 1.6 Ω, R2 = 0.2 Ω, X2 = 0.4 Ω. The transformer ratio is 4:1. Calculate the
approximate equivalent impedance referred to the primary side.
Q7. During a polarity test on a 230/110 V transformer, the measured voltage across the
series combination is 120 V. If the primary is energized at 110 V, determine the
secondary induced voltage and state the polarity.
Q8. A 10 kVA, 250/125 V transformer has winding resistances R1 = 0.6 Ω and R2 = 0.15 Ω.
Find the total copper resistance referred to the low-voltage side.
Q9. The equivalent impedance of a transformer referred to the secondary side is (1 + j2) Ω.
If the turns ratio N1/N2 = 5, calculate the equivalent impedance referred to the primary
side.
Q10. A single-phase transformer has the following parameters referred to the primary side:
Req = 2 Ω and Xeq = 5 Ω. If the primary voltage is 400 V and rated current is 10 A,
calculate the approximate voltage drop in the transformer.
