GATE EE Electrical Machines PYQs & Answers — Page 2

Questions 11–20 of 79. Imported answers require independent review unless marked reviewed.

The transformer connection given in the figure is part of a balanced 3-phase circuit where the phase sequence is “abc”. The primary to secondary turns ratio is 2:1. If

, then the relationship between

and

will be

Diagram for Electrical Engineering question 43

Your answerChoose one option.

and

lags

and

leads

and

lags

and

leads

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A DC series motor with negligible series resistance is running at a certain speed driving a load, where the load torque varies as cube of the speed. The motor is fed from a 400 V DC source and draws 40 A armature current. Assume linear magnetic circuit. The external resistance, in

, that must be connected in series with the armature to reduce the speed of the motor by half, is closest to

Your answerChoose one option.

23.28

4.82

46.7

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A 3-phase, 400 V, 4 pole, 50 Hz star connected induction motor has the following parameters referred to the stator:

Stator resistance, magnetizing reactance and core loss of the motor are neglected. The motor is run with constant V/f control from a drive. For maximum starting torque, the voltage and frequency output, respectively, from the drive, is closest to,

Your answerChoose one option.

400 V and 50 Hz

200 V and 25 Hz

100 V and 12.5 Hz

300 V and 37.5 Hz

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Consider two coupled circuits, having self-inductances

and

, that carry non-zero currents

and

, respectively. The mutual inductance between the circuits is M with unity coupling coefficient. The stored magnetic energy of the coupled circuits is minimum at which of the following value(s) of

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

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Using shunt capacitors, the power factor of a 3-phase, 4 kV induction motor (drawing 390 kVA at 0.77 pf lag) is to be corrected to 0.85 pf lag. The line current of the capacitor bank, in A, is ____________ (round off to one decimal place).

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A three phase, 50 Hz, 6 pole induction motor runs at 960 rpm. The stator copper loss, core loss, and the rotational loss of the motor can be neglected. The percentage efficiency of the motor is

Your answerChoose one option.

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Which one of the following options represents possible voltage polarities in a single phase two winding transformer? Here,

is the applied primary voltage,

is the induced primary voltage,

is the open circuit secondary voltage, and

is the induced secondary voltage.

Your answerChoose one option.

Diagram for Electrical Engineering question 18

Diagram for Electrical Engineering question 18 (figure 2)

Diagram for Electrical Engineering question 18 (figure 3)

Diagram for Electrical Engineering question 18 (figure 4)

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A 3-phase, 11 kV, 10 MVA synchronous generator is connected to an inductive load of power factor

via a lossless line with a per-phase inductive reactance of 5

. The per-phase synchronous reactance of the generator is 30

with negligible armature resistance. If the generator is producing the rated current at the rated voltage, then the power factor at the terminal of the generator is

Your answerChoose one option.

0.63 lagging.

0.87 lagging.

0.63 leading.

0.87 leading.

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A 3-phase star connected slip ring induction motor has the following parameters referred to the stator:

The per phase stator to rotor effective turns ratio is 3:1. The rotor winding is also star connected. The magnetizing reactance and core loss of the motor can be neglected. To have maximum torque at starting, the value of the extra resistance in ohms (referred to the rotor side) to be connected in series with each phase of the rotor winding is ________ (rounded off to 2 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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GATE EE Electrical Machines PYQs

Question 43

Question 44

Question 45

Question 52

Question 63

Question 17

Question 18

Question 40

Question 54

Question 55