TRANSFORMERS MCQs SET 19

TRANSFORMERS MCQs SET 19

1. Which is the correct phasor equation indicating the transformer voltages lagging?
a) V1 = V2 + I*(R cosφ+ X sinφ)
b) V2 = V1 + I*(R cosφ+ X sinφ)
c) V1 = V2 + I*(X cosφ+ X sinφ)
d) V1 = V2 + I*(R cosφ+ R sinφ)
 

Answer: a

2. Which is the correct phasor equation indicating the transformer voltages leading?
a) V1 = V2 + I*(R cosφ- X sinφ)
b) V2 = V1 + I*(R cosφ- X sinφ)
c) V1 = V2 + I*(X cosφ- X sinφ)
d) V1 = V2 + I*(R cosφ- R sinφ)
 

Answer: a

3. What is the correct formula to get power factor angle in leading condition?
a) tan φ= X/R
b) tan φ= R/X
c) cos φ = R/√(R2+X2)
d) cos φ= R/X
 

Answer: b
4. What is the correct formula to get power factor angle in lagging condition?
a) sin φ= X/R
b) tan φ= R/X
c) cos φ = R/√(R2+X2)
d) cos φ= R/X
 

Answer: c

5. Zero voltage regulation of a transformer is achieved at 1 pf leading.
a) True
b) False
 

Answer: b

6. Which of the following is the main advantage of an auto-transformer over a two-winding transformer?
a) Hysteresis losses are reduced
b) Saving in winding material
c) Copper losses are negligible
d) Eddy losses are totally eliminated
 

Answer: b

7. Auto-transformer makes effective saving on copper and copper losses, when its transformation ratio is
a) Approximately equal to one
b) Less than one
c) Great than one
d) Cannot be found
 

Answer: a

8. Total windings present in a autotransformer are __________
a) 1
b) 2
c) 3
d) 4
 

Answer: a
 

9. Autotransformers are particularly economical when _________
a) Voltage ratio is less than 2
b) Voltage ratio is very high
c) Voltage ratio is higher than 2 in smaller range
d) Can be used anywhere
 

Answer: a
10. Which of the following is not true regarding the autotransformer compare to two-winding transformer?
a) Lower reactance
b) Lower losses
c) Higher exciting current
d) Better voltage regulation
 

Answer: c