GATE IN topic:single-phase-transformer PYQs & Answers

Questions 1–9 of 9. Imported answers require independent review unless marked reviewed.

A single phase step-down transformer has a high voltage primary winding and a low voltage secondary winding. The secondary winding is connected to a load impedance

. The impedance

when referred to the primary winding is denoted by

. Which of the following conditions is true?

Your answerChoose one option.

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A single phase transformer has a rating of 10 kVA, 50 Hz, 1100 V/220 V. In an open circuit test with the high voltage side open, the following are obtained:

• Voltage applied to the low voltage winding = 220 V • Measured power = 363 W • Measured current = 2.75 A

Magnetizing reactance

referred to the high voltage winding is ______ Ω. (rounded off to the nearest integer)

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A 2-pole, 50 Hz, 3-phase induction motor supplies power to a certain load at 2970 rpm. The torque-speed curve of this machine follows a linear relationship between synchronous speed and 95 % of synchronous speed. Assume mechanical and stray losses to be zero. If the load torque of the motor is doubled, the new operating speed of the motor, in rpm, is

Your answerChoose one option.

2940

2812

2970

2850

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The circuit given in the figure is driven by a voltage source

V. The system is operating at a frequency of 50 Hz. The transformers are assumed to be ideal. The average power dissipated, in W, in the 50 kΩ resistance is ______ (rounded off to two decimal places).

Diagram for Instrumentation Engineering question 60

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A 50 kVA transformer has an efficiency of 95% at full load and unity power factor. Assume the core losses are negligible. The efficiency of the transformer at 75% of the full load and 0.8 power factor is ________ % (rounded off to one decimal place).

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A short-circuit test is conducted on a single-phase transformer by shorting its secondary. The frequency of input voltage is 1 kHz. The corresponding wattmeter reading, primary current and primary voltage are 8 W, 2 A and 6 V respectively. Assume that the no-load losses and the no-load currents are negligible, and the core has linear magnetic characteristics. Keeping the secondary short, the primary is connected to a 2 V (RMS), 1 kHz sinusoidal source in series with a

mF capacitor. The primary current (RMS) will be _____ A (rounded off to two decimal places).

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A single-phase transformer has a magnetizing inductance of 250 mH and a core loss resistance of 300

, referred to primary side. When excited with a 230 V, 50 Hz sinusoidal supply at the primary, the power factor of the input current drawn, with secondary on open circuit, is ____ (rounded off to two decimal places).

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A single-phase transformer has maximum efficiency of 98%. The core losses are 80 W and the equivalent winding resistance as seen from the primary side is 0.5

. The rated current on the primary side is 25 A. The percentage of the rated input current at which the maximum efficiency occurs is

Your answerChoose one option.

35.7%

50.6%

80.5%

100%

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In the Figures (a) and (b) shown below, the transformers are identical and ideal, except that the transformer in Figure (b) is centre-tapped. Assuming ideal diodes, the ratio of the root-mean-square (RMS) voltage across the resistor

in Figure (a) to that in Figure (b) is

Diagram for Instrumentation Engineering question 4

Your answerChoose one option.

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GATE IN topic:single-phase-transformer PYQs

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