# Questions & Answers of Single Phase Transformer: Equivalent Circuit, Phasor Diagram, Open Circuit and Short Circuit Tests, Regulation and Efficiency

## Weightage of Single Phase Transformer: Equivalent Circuit, Phasor Diagram, Open Circuit and Short Circuit Tests, Regulation and Efficiency

Total 15 Questions have been asked from Single Phase Transformer: Equivalent Circuit, Phasor Diagram, Open Circuit and Short Circuit Tests, Regulation and Efficiency topic of Electrical Machines subject in previous GATE papers. Average marks 1.53.

A single-phase 100 kVA, 1000 V / 100 V, 50 Hz transformer has a voltage drop of 5% across its series impedance at full load. Of this, 3% is due to resistance. The percentage regulation of the transformer at full load with 0.8 lagging power factor is

A single-phase 400 V, 50 Hz transformer has an iron loss of 5000 W at the rated condition. When operated at 200 V, 25 Hz, the iron loss is 2000 W. When operated at 416 V, 52 Hz, the value of the hysteresis loss divided by the eddy current loss is ______.

A single-phase, 22 kVA, 2200 V/ 220 V, 50 Hz, distribution transformer is to be connected as an auto-transformer to get an output voltage of 2420 V. Its maximum kVA rating as an autotransformer is

A single-phase, 2 kVA, 100/200 V transformer is reconnected as an auto-transformer such that its kVA rating is maximum. The new rating, in kVA, is ______.

Three single-phase transformers are connected to form a delta-star three-phase transformer of 110 kV/ 11 kV. The transformer supplies at 11 kV a load of 8 MW at 0.8 p.f. lagging to a nearby plant. Neglect the transformer losses. The ratio of phase currents in delta side to star side is

The self inductance of the primary winding of a single phase, 50 Hz, transformer is 800 mH, and that of the secondary winding is 600 mH. The mutual inductance between these two windings is 480 mH. The secondary winding of this transformer is short circuited and the primary winding is connected to a 50 Hz, single phase, sinusoidal voltage source. The current flowing in both the winding is less than their respective rated currents. The resistance of both windings can be neglected. In this connection, what is the effective inductance (in mH) seen by the source?

Two single-phase transformers T1 and T2 each rated at 500 kVA are operated in parallel. Percentage impedances of T1 and T2 are (1+j6) and (0.8+j4.8), respectively. To share a load of 1000 kVA at 0.8 lagging power factor, the contribution of T2 (in kVA) is _________.

A single phase 10 kVA, 50 Hz transformer with 1 kV primary winding draws 0.5 A and 55 W, at rated voltage and frequency, on no load. A second transformer has a core with all its linear dimensions $\sqrt{2}$ times the corresponding dimensions of the first transformer. The core material and lamination thickness are the same in both transformers. The primary windings of both the transformers have the same number of turns. If a rated voltage of 2 kV at 50 Hz is applied to the primary of the second transformer, then the no load current and power, respectively, are

A single phase air core transformer, fed from a rated sinusoidal supply, is operating at no load. The steady state magnetizing current drawn by the transformer from the supply will have the waveform

A single-phase transformer has a turns ratio of 1:2, and is connected to a purely resistive load as shown in the figure. The magnetizing current drawn is 1A, and the secondary current is 1A. If core losses and leakage reactances are neglected, the primary current is

The single phase, 50Hz, iron core transformer in the circuit has both the vertical arms of cross sectional area 20cm2 and both the horizontal arms of cross sectional area 10cm2. If the two windings shown were wound instead on opposite horizontal arms, the mutual inductance will

Three single-phase transformer are connected to form a 3-phase transformer bank.The transformers are connected in the following manner :

The transformer connecting will be represented by

It is desired to measure parameters of 230 V/115 V, 2 kVA,single-phase transformer. The following wattmeters are available in a laboratory:
W1 : 250 V, 10 A, Low Power Factor
W2 : 250 V, 5 A, Low Power Factor
W3 : 150 V, 10 A, High Power Factor
W4 : 150 V, 5 A, High Power Factor
The Wattmeters used in open circuit test and short circuit test of the transformer will respectively be

The core of a two-winding transformer is subjected to a magnetic flux variation as indicated in the figure.

The induced emf (ers) in the secondary winding as a function of time will be of the form

 (A) (B) (C) (D)

A single-phase, 50 kVA, 250 V/500 V two winding transformer has an efficiency of 95% at full load, unity power factor. If it is re-configured as a 500 V/750 V autotransformer, its efficiency at its new rated load at unity power factor will be