GATE EE 2018 EXAM:Electrical Machines Quiz 5

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Question 1

A 6-pole lap wound d.c. machine armature has 720 conductors and it draws 50 A from supply mains. What is the flux distribution produced by the armature reaction per pole?

• ARectangular in wave shape with a peak of 500 AT
• BRectangular in wave shape with a peak of 100 AT
• CTriangular in wave shape with a peak of 500 AT
• DTriangular in wave shape with a peak of 1000 AT

Question 2

What is the core loss in a high frequency ferrite core transformer used in SMPS power supply?

• A10% of rated power
• B5% of rated power
• C2% of rated power
• D1% of rated power

Question 3

Assertion (A): In a certain case, a d.c. shunt generator failed to build up the voltage.
Reason (R): Shunt field resistance of a.d.c. shunt generator should be more than its critical field resistance value to generate voltage.

• ABoth A and R are true and R is the correct explanation of A
• BBoth A and R are true but R is NOT the correct explanation of A
• CA is true but R is false
• DA is false but R is true

Question 4

Which one of the following statements is correct for the ideal field excitation during starting in case of shunt and compound motors?

• AMaximum because motor torque required to overcome friction and load torque.
• BMaximum, because voltage should be built slowly.
• CMaximum, because small excitation will lead to low operating speed during starting
• DIt can be anything because it does not matter in case of these motors.

Question 5

The armature resistance of a 6-pole lap wound d.c. machine is 0.05 . If the armature is rewound as a wave-winding, what is the armature resistance?

• A
• B
• C
• D

Question 6

The full-load copper loss and iron loss of a transformer are 6400 W and 500 W, respectively. The above copper loss and iron loss at half load will be

• A33200 W and 250 W respectively
• B3200 W and 500 W respectively
• C1600 W and 125 W respectively
• D1600 W and 500 W respectively

Question 7

A 4-pole dc generator is running at 1500 rpm. The frequency of current in the armature winding is

• A50 Hz
• B150 Hz
• C25 Hz
• D100 Hz

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