GATE EE concept:no-load PYQs & Answers

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Questions 1–10 of 12. Imported answers require independent review unless marked reviewed.

Topic practice 12 questionsPage 1 of 2

A 220V/12V single-phase transformer is designed for use in India and rated 100 VA at 50 Hz. Later, this unit is shipped to the USA where it is used as a 110V/6V transformer at 60 Hz.

Which of the following statements is/are correct?

Your answerSelect all correct options. You can choose more than one.

No-load current drawn would be smaller for operation in the USA compared to that in India

For the same load current, the losses would be higher in the USA compared to that in India

The peak magnetic flux density in the core would be higher while operating in the USA compared to that in India

The eddy current losses in the core would be approximately 44% higher while operating in the USA compared to that in India

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The induced emf in a 3 kV, 4 pole, 3-phase star connected synchronous motor is considered to be equal and in phase with the terminal voltage under no load condition. On application of a mechanical load, the induced emf phasor is deflected by an angle of 2° mechanical with respect to the terminal voltage phasor. If the synchronous reactance is

, and stator resistance is negligible, then the motor armature current magnitude, in ampere, during loaded condition is closest to, __________ (round off to two decimal places).

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A 5 kW, 220 V DC shunt motor has 0.5

armature resistance including brushes. The motor draws a no-load current of 3 A. The field current is constant at 1 A. Assuming that the core and rotational losses are constant and independent of the load, the current (in amperes) drawn by the motor while delivering the rated load, for the best possible efficiency, is ________ (rounded off to 2 decimal places).

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A 3-phase, 415 V, 4-pole, 50 Hz induction motor draws 5 times the rated current at rated voltage at starting. It is required to bring down the starting current from the supply to 2 times of the rated current using a 3-phase autotransformer. If the magnetizing impedance of the induction motor and no load current of the autotransformer is neglected, then the transformation ratio of the autotransformer is given by ____________. (round off to two decimal places).

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A three-phase, 50 Hz, 4-pole induction motor runs at no-load with a slip of 1 %. With full load, the slip increases to 5 %. The % speed regulation of the motor (rounded off to 2 decimal places) is ____________.

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A single-phase, 4 kVA, 200 V/100 V, 50 Hz transformer with laminated CRGO steel core has rated no-load loss of 450 W. When the high-voltage winding is excited with 160 V, 40 Hz sinusoidal ac supply, the no-load losses are found to be 320 W. When the high-voltage winding of the same transformer is supplied from a 100 V, 25 Hz sinusoidal ac source, the no-load losses will be ________ W (rounded off to 2 decimal places).

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A 250 V dc shunt motor has an armature resistance of 0.2

and a field resistance of 100

. When the motor is operated on no-load at rated voltage, it draws an armature current of 5 A and runs at 1200 rpm. When a load is coupled to the motor, it draws total line current of 50 A at rated voltage, with a 5 % reduction in the air-gap flux due to armature reaction. Voltage drop across the brushes can be taken as 1 V per brush under all operating conditions. The speed of the motor, in rpm, under this load condition, is closest to:

Your answerChoose one option.

1200

1000

1220

900

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Windings ‘A’, ‘B’ and ‘C’ have 20 turns each and are wound on the same iron core as shown, along with winding ‘X’ which has 2 turns. The figure shows the sense (clockwise/anti-clockwise) of each of the windings only and does not reflect the exact number of turns. If windings ‘A’, ‘B’ and ‘C’ are supplied with balanced 3-phase voltages at 50 Hz and there is no core saturation, the no-load RMS voltage (in V, rounded off to 2 decimal places) across winding ‘X’ is ______.

Diagram for Electrical Engineering question 48

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A 220 V DC shunt motor takes 3 A at no-load. It draws 25 A when running at full-load at 1500 rpm. The armature and shunt resistances are 0.5 Ω and 220 Ω, respectively. The no-load speed in rpm (round off to two decimal places) is __________.

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A separately excited dc motor has an armature resistance

. The field excitation is kept constant. At an armature voltage of 100 V, the motor produces a torque of 500 Nm at zero speed. Neglecting all mechanical losses, the no-load speed of the motor (in radians/s) for an armature voltage of 150 V is ____ (up to 2 decimal places).

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GATE EE concept:no-load PYQs

How to practice concept:no-load

Question 31

Question 35

Question 55

Question 65

Question 17

Question 21

Question 28

Question 48

Question 46

Question 24