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# AE-JE Foundation EE: Electrical Machines Quiz 1

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Question 1

A single-phase transformer has R(p.u.) = 0.4 p.u. and X(p.u.) = 0.6 p.u. At what power factor, the voltage regulation will be zero?

Question 2

Consider the following statements regarding transformers:
1) The function of the magnetizing component of no load current is to sustain the alternating flux in the core.
2) Short circuit test is performed to find core losses only.
3) The function of the breather in transformer is to arrest flow of moisture when outside air enters the transformer.
Which of these statements are correct?

Question 3

What is the load at which maximum efficiency occurs in case of a 100 kVA transformer with iron loss of 1 kW and full-load copper loss of 2 kW?

Question 4

Assertion (A): In a transformer, open circuit (OC) test is conducted from low voltage side and short circuit (SC) test conducted froth high voltage side.
Reason (R): OC test gives iron loss and SC test gives copper loss.

Question 5

A 2 V/1 V two winding transformer is connected as an autotransformer. Its voltage regulation as an autotransformer compared to the two winding transformer is

Question 6

If a transformer core has air gaps, then

Question 7

A transformer having 1000 turns is connected to a 250 V ac supply for a secondary voltage of 400 V. Then the number of secondary turns should be

Question 8

A transformer has hysteresis loss of 30 Watts at 240 V 60 Hz supply. The hysteresis loss at 200V, 50 Hz supply is

Question 9

A transformer has a reactance of 0.1 pu and negligible resistance. What is its voltage regulation at full load, and 0.8 power factor lagging?

Question 10

Two 40 kVA single phase transformer are connected in open delta to supply a 230 V balanced 3-phase load. What is the total load that can be supplied without overloading either transformer?
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