223 + Mcqs in Transformers Page 4 McqOptions

151.	Which of the following protection is normally not provided on small distribution transformers?
A.	Overfluxing protection
B.	Buchholz relay
C.	Overcurrent protection
D.	All of the above
Answer» C. Overcurrent protection

Discussion

152.	The maximum efficiency of a distribution transformer is
A.	at no load
B.	at 50% full load
C.	at 80% full load
D.	at full load
Answer» C. at 80% full load

Discussion

153.	Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect?
A.	Its secondary current is 5 A
B.	Its secondary voltage is 400 V
C.	Its rating is 2 kVA
D.	Its secondary current is 20 A
Answer» E.

Discussion

154.	Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in
A.	short-circuiting of the secondaries
B.	power factor of one of the transformers is leading while that of the other lagging
C.	transformers having higher copper losses will have negligible core losses
D.	loading of the transformers not in proportion to their kVA ratings
Answer» E.

Discussion

155.	The function of breather in a transformer is
A.	to provide oxygen inside the tank
B.	to cool the coils during reduced load
C.	to cool the transformer oil
D.	to arrest flow of moisture when outside air enters the transformer
Answer» E.

Discussion

156.	The function of conservator in a transformer is
A.	to project against internal fault
B.	to reduce copper as well as core losses
C.	to cool the transformer oil
D.	to take care of the expansion and contraction of transformer oil due to variation of temper-ature of sur-roundings
Answer» E.

Discussion

157.	The chemical used in breather for transformer should have the quality of
A.	ionizing air
B.	absorbing moisture
C.	cleansing the transformer oil
D.	cooling the transformer oil
Answer» C. cleansing the transformer oil

Discussion

158.	The no-load current drawn by transformer is usually what per cent of the full-load current?
A.	0.2 to 0.5 per cent
B.	2 to 5 per cent
C.	12 to 15 per cent
D.	20 to 30 per cent
Answer» C. 12 to 15 per cent

Discussion

159.	The transformer ratings are usually expressed in terms of
A.	volts
B.	amperes
C.	kW
D.	kVA
Answer» E.

Discussion

160.	Delta/star transformer works satisfactorily when
A.	load is balanced only
B.	load is unbalanced only
C.	on balanced as well as unbalanced loads
D.	none of the above
Answer» D. none of the above

Discussion

161.	Star/star transformers work satisfactorily when
A.	load is unbalanced only
B.	load is balanced only
C.	on balanced as well as unbalanced loads
D.	none of the above
Answer» C. on balanced as well as unbalanced loads

Discussion

162.	The changes in volume of transformer cooling oil due to variation of atmospheric tem-perature during day and night is taken care of by which part of transformer
A.	Conservator
B.	Breather
C.	Bushings
D.	Buchholz relay
Answer» B. Breather

Discussion

163.	In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are
A.	friction and windage losses
B.	copper losses
C.	hysteresis and eddy current losses
D.	none of the above
Answer» D. none of the above

Discussion

164.	The value of flux involved m the e.m.f. equation of a transformer is
A.	average value
B.	r.m.s. value
C.	maximum value
D.	instantaneous value
Answer» D. instantaneous value

Discussion

165.	The chemical used in breather is
A.	asbestos fiber
B.	silica sand
C.	sodium chloride
D.	silica gel
Answer» E.

Discussion

166.	In an actual transformer the iron loss remains practically constant from noload to fullload because
A.	value of transformation ratio remains constant
B.	permeability of transformer core remains constant
C.	core flux remains practically constant
D.	primary voltage remains constant
Answer» D. primary voltage remains constant

Discussion

167.	For given applied voltage, with the increase in frequency of the applied voltage
A.	eddy current loss will decrease
B.	eddy current loss will increase
C.	eddy current loss will remain unchanged
D.	none of the above
Answer» D. none of the above

Discussion

168.	Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds
A.	50°C
B.	80°C
C.	100°C
D.	150°C
Answer» E.

Discussion

169.	In a transformer the resistance between its primary and secondary should be
A.	zero
B.	10 Q
C.	1000 Q
D.	infinity
Answer» E.

Discussion

170.	The highest voltage for transmitting electrical power in India is
A.	33 kV
B.	66 kV
C.	132 kV
D.	400 kV
Answer» E.

Discussion

171.	Minimum voltage regulation occurs when the power factor of the load is
A.	unity
B.	lagging
C.	leading
D.	zero
Answer» D. zero

Discussion

172.	If the supply frequency to the transformer is increased, the iron loss will
A.	not change
B.	decrease
C.	increase
D.	any of the above
Answer» D. any of the above

Discussion

173.	In case of a double cage induction motor, the inner cage has
A.	high inductance arid low resistance
B.	low inductance and high resistance
C.	low inductance and low resistance
D.	high inductance and high resistance
Answer» B. low inductance and high resistance

Discussion

174.	The thickness of laminations used in a transformer is usually
A.	0.4 mm to 0.5 mm
B.	4 mm to 5 mm
C.	14 mm to 15 mm
D.	25 mm to 40 mm
Answer» B. 4 mm to 5 mm

Discussion

175.	The degree of mechanical vibrations produced by the laminations of a transformer depends on
A.	tightness of clamping
B.	gauge of laminations
C.	size of laminations
D.	all of the above
Answer» E.

Discussion

176.	The transformer oil should have _____ volatility and _____ viscosity.
A.	low,low
B.	high,high
C.	low,high
D.	high,low
Answer» B. high,high

Discussion

177.	If a transformer is switched on to a voltage more than the rated voltage
A.	its power factor will deteriorate
B.	its power factor will increase
C.	its power factor will remain unaffected
D.	its power factor will be zero
Answer» B. its power factor will increase

Discussion

178.	The secondary winding of which of the following transformers is always kept closed?
A.	Step-up transformer
B.	Step-down transformer
C.	Potential transformer
D.	Current transformer
Answer» E.

Discussion

179.	Power transformers are designed to have maximum efficiency at
A.	nearly full load
B.	70% full load
C.	50% full load
D.	no load
Answer» B. 70% full load

Discussion

180.	A transformer can have regulation closer to zero
A.	on full-load
B.	on overload
C.	on leading power factor
D.	on zero power factor
Answer» D. on zero power factor

Discussion

181.	In a transformer the resistance between its primary and secondary is
A.	zero
B.	1 ohm
C.	1000 ohms
D.	infinite
Answer» E.

Discussion

182.	A transformer transforms
A.	voltage
B.	current
C.	power
D.	frequency
Answer» D. frequency

Discussion

183.	The core used in high frequency transformer is usually
A.	copper core
B.	cost iron core
C.	air core
D.	mild steel core
Answer» D. mild steel core

Discussion

184.	Helical coils can be used on
A.	low voltage side of high kVA transformers
B.	high frequency transformers
C.	high voltage side of small capacity transformers
D.	high voltage side of high kVA rating transformers
Answer» B. high frequency transformers

Discussion

185.	For a transformer, operating at constant load current, maximum efficiency will occur at
A.	0.8 leading power factor
B.	0.8 lagging power factor
C.	zero power factor
D.	unity power factor
Answer» E.

Discussion

186.	The efficiency of two identical transformers under load conditions can be determined by
A.	short-circuit test
B.	back-to-back test
C.	open circuit test
D.	any of the above
Answer» C. open circuit test

Discussion

187.	The no load current in a transformer lags behind the applied voltage by an angle of about
A.	180°
B.	120°
C.	90°
D.	75°
Answer» E.

Discussion

188.	Hysteresis loss in a transformer varies as (Bmax = maximum flux density)
A.	Bmax
B.	Bmax1-6
C.	Bmax1-83
D.	B max
Answer» C. Bmax1-83

Discussion

189.	If the current drawn in the secondary of a transformer increases, the power in the primary should remain the same.
A.	1
B.
Answer» C.

Discussion

190.	The voltage V2 is _____ in the given circuit.
A.	36.7 V
B.	73.3 V
C.	110 V
D.	220 V
Answer» B. 73.3 V

Discussion

191.	___ is the concept of one coil inducing a voltage into another coil.
A.	Electrical isolation
B.	Self-inductance
C.	Mutual inductance
D.	Coefficient of coupling
Answer» D. Coefficient of coupling

Discussion

192.	A step-up transformer will ___ to the secondary.
A.	increase the current
B.	increase the voltage
C.	increase the power
D.	decrease the voltage
Answer» C. increase the power

Discussion

193.	In the given circuit, Maximum power is being transferred to the load.
A.	1
B.
Answer» C.

Discussion

194.	Regardless of whether the transformer is step-up or step-down, power in the primary equals the power in the secondary if there is 100% efficiency.
A.	1
B.
Answer» B.

Discussion

195.	A(n) _____ transformer is usually used for audio or power applications.
A.	iron-core
B.	air-core
C.	ferrite-core
D.	All of the above
Answer» B. air-core

Discussion

196.	For mutual inductance to occur, the two coils must be at right angles to each other.
A.	1
B.
Answer» C.

Discussion

197.	The reflected resistance is ___ as seen by the source in the given circu.
A.	150
B.	300
C.	600
D.	2.4 k
Answer» E.

Discussion

198.	An open secondary winding of a transformer will cause the primary current to be nearly zero.
A.	1
B.
Answer» B.

Discussion

199.	If the primary power of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary power is
A.	100 W
B.	50 W
C.	75 W
D.	200 W
Answer» B. 50 W

Discussion

200.	A(n) ___ is sometimes constructed as a variable transformer.
A.	autotransformer
B.	center-tapped transformer
C.	multiple-tap transformer
D.	multiple-winding transformer
Answer» B. center-tapped transformer

Discussion

Explore topic-wise MCQs in Electronics.

Which of the following protection is normally not provided on small distribution transformers?

The maximum efficiency of a distribution transformer is

Which of the following statements regarding an idel single-phase transformer having a turn ratio of 1 : 2 and drawing a current of 10 A from 200 V A.C. supply is incorrect?

Two transformers are connected in parallel. These transformers do not have equal percentage impedance. This is likely to result in

The function of breather in a transformer is

The function of conservator in a transformer is

The chemical used in breather for transformer should have the quality of

The no-load current drawn by transformer is usually what per cent of the full-load current?

The transformer ratings are usually expressed in terms of

Delta/star transformer works satisfactorily when

Star/star transformers work satisfactorily when

The changes in volume of transformer cooling oil due to variation of atmospheric tem-perature during day and night is taken care of by which part of transformer

In a given transformer for given applied voltage, losses which remain constant irrespective of load changes are

The value of flux involved m the e.m.f. equation of a transformer is

The chemical used in breather is

In an actual transformer the iron loss remains practically constant from noload to fullload because

For given applied voltage, with the increase in frequency of the applied voltage

Gas is usually not liberated due to dissociation of transformer oil unless the oil temperature exceeds

In a transformer the resistance between its primary and secondary should be

The highest voltage for transmitting electrical power in India is

Minimum voltage regulation occurs when the power factor of the load is

If the supply frequency to the transformer is increased, the iron loss will

In case of a double cage induction motor, the inner cage has

The thickness of laminations used in a transformer is usually

The degree of mechanical vibrations produced by the laminations of a transformer depends on

The transformer oil should have _____ volatility and _____ viscosity.

If a transformer is switched on to a voltage more than the rated voltage

The secondary winding of which of the following transformers is always kept closed?

Power transformers are designed to have maximum efficiency at

A transformer can have regulation closer to zero

In a transformer the resistance between its primary and secondary is

A transformer transforms

The core used in high frequency transformer is usually

Helical coils can be used on

For a transformer, operating at constant load current, maximum efficiency will occur at

The efficiency of two identical transformers under load conditions can be determined by

The no load current in a transformer lags behind the applied voltage by an angle of about

Hysteresis loss in a transformer varies as (Bmax = maximum flux density)

If the current drawn in the secondary of a transformer increases, the power in the primary should remain the same.

The voltage V2 is _____ in the given circuit.

___ is the concept of one coil inducing a voltage into another coil.

A step-up transformer will ___ to the secondary.

In the given circuit, Maximum power is being transferred to the load.

Regardless of whether the transformer is step-up or step-down, power in the primary equals the power in the secondary if there is 100% efficiency.

A(n) _____ transformer is usually used for audio or power applications.

For mutual inductance to occur, the two coils must be at right angles to each other.

The reflected resistance is ___ as seen by the source in the given circu.

An open secondary winding of a transformer will cause the primary current to be nearly zero.

If the primary power of an ideal transformer having a 2:1 voltage ratio is 100 W, the secondary power is

A(n) ___ is sometimes constructed as a variable transformer.

The transformer oil should have _ volatility and _ viscosity.