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Transformer Mcqs

Q:

For a transformer with primary turns 400, secondary turns 100, if 20A current is flowing through primary, we will get ___________

A) 80A at secondary B) 5A at secondary
C) 800A at secondary D) 40A at secondary
 
Answer & Explanation Answer: A) 80A at secondary

Explanation: Current in the primary of the transformer will get modified in the transformer secondary, according to the number of turns, in inverse proportion. Thus, turns are modified with 1/4 times the primary, we’ll get 4 times higher current at secondary.

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3951
Q:

For a transformer with primary turns 100, secondary turns 400, if 200 V is applied at primary we will get ___________

A) 80 V at secondary B) 800 V at secondary
C) 1600 V at secondary D) 3200 V at secondary
 
Answer & Explanation Answer: B) 800 V at secondary

Explanation: Voltage in the primary of the transformer will get modified in the transformer secondary, according to the number of turns. Thus, turns are modified with 4 times the primary, we’ll get 4 times higher voltage at secondary.

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2834
Q:

A 25 KVA transformer is constructed to a turns ratio of N1/N2 = 10. The impedance of primary winding is 3+j5 ohms and of secondary winding is 0.5+j0.8 ohms. What will be the impedance of transformer when referred to primary?

A) 53j + 85 ohms B) 53 + 85j ohms
C) 3.5 + 5.8j ohms D) Can’t be calculated
 
Answer & Explanation Answer: B) 53 + 85j ohms

Explanation: Not available for this question

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1218
Q:

For a power transformer operating at full load it draws voltage and current equal to 200 V and 100 A respectively at 0.8 pf. Iron and copper losses are equal to 120 kW and 300kW. What is the efficiency?

A) 86.44% B) 96.44%
C) 97.44% D) 99.12%
 
Answer & Explanation Answer: C) 97.44%

Explanation: Power output= VI cos?= 200*100*0.8 = 16000 W (Independent of lag and lead). While total losses are equal to iron loss+ k2*copper losses =120+ 300= 420 W. Efficiency is equal to 1- 420/(16000+420)= 97.44%.

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1131
Q:

Voltage transformers are designed to have _____________

A) high leakage reactance B) high magnetizing current
C) high magnetizing reactance D) low magnetizing reactance
 
Answer & Explanation Answer: C) high magnetizing reactance

Explanation: Voltage transformers often known as potential transformers are designed with minimum errors and to achieve this they are constructed with low leakage reactance, low loss and high magnetizing reactance.

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783
Q:

Total windings present in a autotransformer are __________

A) 1 B) 2
C) 3 D) 4
 
Answer & Explanation Answer: A) 1

Explanation: Autotransformer is the special transformer for which the single winding acts as a primary and secondary both. Thus, by taking the appropriate winding into consideration a variable secondary voltage is obtained.

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780
Q:

Turns ratio of the transformer is directly proportional to ____________

A) Resistance ratio B) Currents ratio
C) Voltage ratio D) Not proportional to any terms
 
Answer & Explanation Answer: C) Voltage ratio

Explanation: According to the voltage expression, emf induced in the primary is directly proportional to the change in the flux with respect to the time and number of turns of the primary winding. Similarly, for secondary winding.

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638
Q:

To convert an ideal transformer into a practical transformer we add ____________

A) Primary winding resistance and secondary winding resistance B) Primary winding leakage reactance and secondary winding leakage reactance
C) Primary winding resistance, leakage and secondary winding leakage reactance D) Cannot be determined
 
Answer & Explanation Answer: C) Primary winding resistance, leakage and secondary winding leakage reactance

Explanation: We consider all resistances i.e. of primary and secondary as series parameters of equivalent circuit of transformer, while all leakage reactances are also connected into the circuit as series parameters.

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