GATE EE Electrical Machines PYQs & Answers — Page 3

Questions 21–30 of 79. Imported answers require independent review unless marked reviewed.

A single-phase full-controlled thyristor converter bridge is used for regenerative braking of a separately excited DC motor with the following specifications:

Specification	Value
Rated armature voltage	210 V
Rated armature current	10 A
Rated speed	1200 rpm
Armature resistance	1 Ω
Input to the converter bridge	240 V at 50 Hz
The armature of the DC motor is fed from the full-controlled bridge and the field current is kept constant.

Assume that the motor is running at 600 rpm and the armature terminals of the motor are suitably reversed for regenerative braking. If the armature current of the motor is to be maintained at the rated value, the triggering angle of the converter bridge in degrees should be ______ (rounded off to 2 decimal places).

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The following columns present various modes of induction machine operation and the ranges of slip

Column A: Mode of operation	Column B: Range of Slip
a. Running in generator mode	p) From 0.0 to 1.0
b. Running in motor mode	q) From 1.0 to 2.0
c. Plugging in motor mode	r) From -1.0 to 0.0

The correct match between the elements in column A with those of column B is

Your answerChoose one option.

a-r, b-p, and c-q

a-r, b-q, and c-p

a-p, b-r, and c-q

a-q, b-p, and c-r

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A 10-pole, 50 Hz, 240 V, single phase induction motor runs at 540 RPM while driving rated load. The frequency of induced rotor currents due to backward field is

Your answerChoose one option.

100 Hz

95 Hz

10 Hz

5 Hz

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The four stator conductors (A, A′, B and B′) of a rotating machine are carrying DC currents of the same value, the directions of which are shown in the figure (i). The rotor coils a-a′ and b-b′ are formed by connecting the back ends of conductors ‘a’ and ‘a′’ and ‘b’ and ‘b′’, respectively, as shown in figure (ii). The e.m.f. induced in coil a-a′ and coil b-b′ are denoted by Eₐ₋ₐ′ and Eᵦ₋ᆼ′, respectively. If the rotor is rotated at uniform angular speed ω rad/s in the clockwise direction then which of the following correctly describes the Eₐ₋ₐ′ and Eᵦ₋ᆼ′?

Diagram for Electrical Engineering question 22

Your answerChoose one option.

Eₐ₋ₐ′ and Eᵦ₋ᆼ′ have finite magnitudes and are in the same phase

Eₐ₋ₐ′ and Eᵦ₋ᆼ′ have finite magnitudes with Eᵦ₋ᆼ′ lead Eₐ₋ₐ′

Eₐ₋ₐ′ and Eᵦ₋ᆼ′ have finite magnitudes with Eₐ₋ₐ′ lead Eᵦ₋ᆼ′

Eₐ₋ₐ′ = Eᵦ₋ᆼ′ = 0

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A separately excited DC motor rated 400 V, 15 A, 1500 RPM drives a constant torque load at rated speed operating from 400 V DC supply drawing rated current. The armature resistance is 1.2 Ω. If the supply voltage drops by 10% with field current unaltered then the resultant speed of the motor in RPM is __________ (Round off to the nearest integer).

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A three-phase synchronous motor with synchronous impedance of

per unit per phase has a static stability limit of 2.5 per unit. The corresponding excitation voltage in per unit is __________ (Round off to 2 decimal places).

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A three phase 415 V, 50 Hz, 6-pole, 960 RPM, 4 HP squirrel cage induction motor drives a constant torque load at rated speed operating from rated supply and delivering rated output. If the supply voltage and frequency are reduced by 20%, the resultant speed of the motor in RPM (neglecting the stator leakage impedance and rotational losses) is _________ (Round off to the nearest integer).

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When the winding c-d of the single-phase, 50 Hz, two winding transformer is supplied from an AC current source of frequency 50 Hz, the rated voltage of 200 V (rms), 50 Hz is obtained at the open-circuited terminals a-b. The cross sectional area of the core is 500 mm

and the average core length traversed by the mutual flux is 500 mm. The maximum allowable flux density in the core is

Wb/m

and the relative permeability of the core material is 5000. The leakage impedance of the winding a-b and winding c-d at 50 Hz are

and

, respectively. Considering the magnetizing characteristics to be linear and neglecting core loss, the self-inductance of the winding a-b in millihenry is __________ (Round off to 1 decimal place).

Diagram for Electrical Engineering question 53

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The most common used relay, for the protection of an alternator against loss of excitation, is

Your answerChoose one option.

offset he relay.

over current relay.

differential relay.

Buchholz relay.

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The type of single-phase induction motor, expected to have the maximum power factor during steady state running condition, is

Your answerChoose one option.

split phase (resistance start).

shaded pole.

capacitor start.

capacitor start, capacitor run.

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GATE EE Electrical Machines PYQs

Question 65

Question 15

Question 16

Question 22

Question 30

Question 47

Question 48

Question 53

Question 13

Question 24