Breather is provided in a transformer to

absorb moisture of air during breathing

provide cold air in transformer

absorb moisture from air entering in transformer

Power loss in a transformer is known as the _____.

Difference of current between the secondary and the primary coils.

Addition of power in the secondary and the primary coils.

difference of voltage between the secondary and the primary coils.

Difference of power between the primary and the secondary coils

Directions: It consists of two statements, one labeled as the ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answer using the codes given below:Statement (I): The magnetization curve of the actual power transformer is non-linear and its effect is to introduce higher-order harmonics in the magnetizing currentStatement (II): The effect of the harmonic frequencies can be taken care of by modifying the magnitudes of the phasors involved, and the phasor diagram at the fundamental frequency, with the assumption of a linear magnetization, remains unaffected.

Statement (I) is true but statement (II) is false

Statement (I) and Statement (II) are individually true and statement (II) is the correct explanation of statement (II)

Statement (I) and Statement (II) are individually true but statement (II) is not the correct explanation of statement (I)

Statement (I) is true but statement (II) is false

Statement (I) is false but statement (II) is true

On the two sides of a star/delta transformer ________

the voltage differ in phase by 30° but currents are in phase

the voltage and current are both in phase

the voltage and current both differ in phase by 30°

the voltage differ in phase by 30° but currents are in phase

the current differ in phase by 30° but voltages are in phase

A transformer operates most efficiently at 3/4th full load. Its iron loss (Pi) and full load copper loss (Pc) are related as

\(\frac{{{P_i}}}{{{P_c}}} = \frac{{16}}{9}\)

\(\frac{{{P_i}}}{{{P_c}}} = \frac{3}{4}\)

\(\frac{{{P_i}}}{{{P_c}}} = \frac{4}{3}\)

\(\frac{{{P_i}}}{{{P_c}}} = \frac{9}{{16}}\)

In a transformer operating at a constant voltage, if the input frequency increases, the core loss:

Increases as square of the frequency

In the equivalent circuit of transformers the magnetizing circuit branch is drawn in parallel to supply voltage because

transformer’s voltage regulation is better

transformer has better operational efficiency

transformer has almost equal iron loss and copper loss

transformer’s magnetization current and iron loss remains constant with supply voltage

transformer’s voltage regulation is better

If the percentage impedances of the two transformers working in parallel are different then

Transformers will be overheated

Power factors of both the transformers will be same

Parallel operation will not be possible

Parallel operation will still be possible

No iron losses means _______ are zero.

hysteresis and eddy current losses

In an ideal transformer, which of the following statement is correct?

no voltage drops in resistance or leakage reactance

mmf required to maintain main flux is small

Auto transformer is used in transmission and distribution.

When iron losses are to be reduced

When efficiency consideration is ignored

When transformation ratio is small

Cores of large power transformers are made from which one of the following?

Cold-rolled non-grain oriented steel

Cold-rolled gain oriented steel

During short-circuit test of a transformer, core losses are negligible because

full-load current is not supplied to the transformer

the current on the secondary side is rated current

the voltage on the secondary side is zero

the voltage applied on the primary side is low

full-load current is not supplied to the transformer

Distribution transformers have core losses:

Negligible compared to full load copper losses

More than full load copper losses

Equal to full load copper losses

Less than full load copper losses

Negligible compared to full load copper losses

293 + Mcqs in Ideal Transformer Page 4 McqOptions

151.	A 10 kVA 500/100 V transformer has the resistance referred to primary is 0.3 Ω. The equivalent resistance of transformer referred to secondary is:
A.	0.10 Ω
B.	7.5 Ω
C.	0.012 Ω
D.	0.21 Ω
Answer» D. 0.21 Ω

Discussion

152.	Find primary turns of a 444 V/222 V, 50 Hz single-phase transformer with a core cross-sectional area of 100 cm2, and a maximum flux density of 1.0 T?
A.	100
B.	200
C.	222
D.	400
Answer» C. 222

Discussion

153.	In a transformer, _________ losses are reduced by decreasing the thickness of lamination of magnetic core and yoke.
A.	copper
B.	eddy current
C.	hysteresis
D.	air friction
Answer» C. hysteresis

Discussion

154.	Breather is provided in a transformer to
A.	absorb moisture of air during breathing
B.	provide cold air in transformer
C.	absorb moisture from air entering in transformer
D.	filter the transformer oil
Answer» D. filter the transformer oil

Discussion

155.	A 4 kVA transformer has iron-loss of 200 W and full load copper loss of 200 W. The maximum efficiency at unity power factor will be
A.	90.9%
B.	85.6%
C.	80.6%
D.	70.9%
Answer» B. 85.6%

Discussion

156.	A dc voltage supply provides 60 V when the output is unloaded. When connected to a load, the output voltage drops to 56 V. The value of the voltage regulation is
A.	3.7%
B.	5.7%
C.	7.1%
D.	9.1%
Answer» D. 9.1%

Discussion

157.	Power loss in a transformer is known as the _____.
A.	Difference of current between the secondary and the primary coils.
B.	Addition of power in the secondary and the primary coils.
C.	difference of voltage between the secondary and the primary coils.
D.	Difference of power between the primary and the secondary coils
Answer» E.

Discussion

158.	Directions: It consists of two statements, one labeled as the ‘Statement (I)’ and the other as ‘Statement (II)’. Examine these two statements carefully and select the answer using the codes given below:Statement (I): The magnetization curve of the actual power transformer is non-linear and its effect is to introduce higher-order harmonics in the magnetizing currentStatement (II): The effect of the harmonic frequencies can be taken care of by modifying the magnitudes of the phasors involved, and the phasor diagram at the fundamental frequency, with the assumption of a linear magnetization, remains unaffected.
A.	Statement (I) and Statement (II) are individually true and statement (II) is the correct explanation of statement (II)
B.	Statement (I) and Statement (II) are individually true but statement (II) is not the correct explanation of statement (I)
C.	Statement (I) is true but statement (II) is false
D.	Statement (I) is false but statement (II) is true
Answer» C. Statement (I) is true but statement (II) is false

Discussion

159.	A single-phase, \(22\;kVA,\;2200\;V/\;220\;V,\;50\;Hz\), distribution transformer is to be connected as an auto-transformer to get an output voltage of \(2420\;V\). Its maximum \(kVA\) rating as an auto-transformer is
A.	22
B.	24.2
C.	242
D.	2420
Answer» D. 2420

Discussion

160.	Distribution transformers are designed to have maximum efficiency nearly at:
A.	100% of full load
B.	50% of full load
C.	25% of full load
D.	10% of full load
Answer» C. 25% of full load

Discussion

161.	In a Scott-connected transformer the number of primary and teaser turns respectively are ____
A.	N, 2N/√3
B.	N/2, N
C.	√3N/2, N
D.	N, √3N/2
Answer» E.

Discussion

162.	Core lamination in a transformer decreases _______.
A.	eddy current loss
B.	hysteresis loss
C.	copper loss
D.	leakage reactance
Answer» B. hysteresis loss

Discussion

163.	A 100 VA, 120/12 V transformer is to be connected so as to form a step-up transformer. A Primary voltage of 120 V is applied to the transformer. What is the secondary voltage of the transformer?
A.	1.2 V
B.	12 V
C.	120 V
D.	132 V
Answer» E.

Discussion

164.	A 20 turns iron cored inductor is connected to a 100 V, 50 Hz source. The maximum flux density in the core is 1 wb/m2. The cross-sectional area of the core in the transformer is
A.	0.155 m2
B.	0.225 m2
C.	0.022 m2
D.	0.35 m2
Answer» D. 0.35 m2

Discussion

165.	On the two sides of a star/delta transformer ________
A.	the voltage and current are both in phase
B.	the voltage and current both differ in phase by 30°
C.	the voltage differ in phase by 30° but currents are in phase
D.	the current differ in phase by 30° but voltages are in phase
Answer» C. the voltage differ in phase by 30° but currents are in phase

Discussion

166.	Hysteresis loss can be minimized by selecting a material for the core that has:
A.	Low hysteresis coefficient
B.	Low transmission coefficient
C.	Unit hysteresis coefficient
D.	High hysteresis coefficient
Answer» B. Low transmission coefficient

Discussion

167.	During the short circuit test on a small transformer, the frequency is increased from 50 Hz to 200 Hz, the copper losses will decrease by a factor of:
A.	16
B.	4
C.	1
D.	1/4
Answer» B. 4

Discussion

168.	A transformer operates most efficiently at 3/4th full load. Its iron loss (Pi) and full load copper loss (Pc) are related as
A.	\(\frac{{{P_i}}}{{{P_c}}} = \frac{{16}}{9}\)
B.	\(\frac{{{P_i}}}{{{P_c}}} = \frac{3}{4}\)
C.	\(\frac{{{P_i}}}{{{P_c}}} = \frac{4}{3}\)
D.	\(\frac{{{P_i}}}{{{P_c}}} = \frac{9}{{16}}\)
Answer» E.

Discussion

169.	A 2000/200 V, 50 Hz single-phase transformer has an exciting current of 0.5 A and a core-loss of 600 W. When H.V side is energized by the rate voltage and frequency, the magnetizing current is
A.	0.1 A
B.	0.2 A
C.	0.3 A
D.	0.4 A
Answer» E.

Discussion

170.	A 1-ϕ transformer has total iron losses of 2500 W at 50 Hz and 400 V input supply voltage. When the applied voltage is 200 V and supply frequency is 25 Hz, the total iron loss is found to be 850 W. Calculate the eddy current loss at 400 V 50 Hz. (Consider V/f ratio as constant)
A.	2000 W
B.	1600 W
C.	1500 W
D.	1000 W
Answer» C. 1500 W

Discussion

171.	A saturable core reactor is basically a
A.	Variable resistor
B.	Thermal relay
C.	Step-down transformer
D.	Variable impedance
Answer» E.

Discussion

172.	In a transformer operating at a constant voltage, if the input frequency increases, the core loss:
A.	Increases
B.	Decreases
C.	Remains constant
D.	Increases as square of the frequency
Answer» C. Remains constant

Discussion

173.	A transformer has a core loss of 140 W at 40 Hz, and 99 W at 30 Hz. The hysteresis and eddy-current losses at 50 Hz, respectively, are
A.	110 W and 30 W
B.	135 W and 30 W
C.	110 W and 50 W
D.	135 W and 50 W
Answer» E.

Discussion

174.	If the pu impedance of a single-phase transformer is 0.01 + j0.05, then its regulation at p.f. of 0.8 lagging will be ______.
A.	+2.2%
B.	-3.8%
C.	+3.8%
D.	-2.2%
Answer» D. -2.2%

Discussion

175.	In a transformer the core loss is 100 Watt at 40 Hz and 72 Watt at 30 Hz, then eddy current and hysteresis losses at 50 Hz respectively are
A.	25 Watt and 105 Watt
B.	20 Watt and 100 Watt
C.	100 Watt and 32 Watt
D.	32 Watt and 100 Watt
Answer» B. 20 Watt and 100 Watt

Discussion

176.	Calculate the regulation of the transformer in which ohmic loss is 1% of the output and reactance drop is 5% of the voltage when the power factor is 0.8 lag
A.	3.8%
B.	3.5%
C.	1%
D.	5%
Answer» B. 3.5%

Discussion

177.	An ideal transformer will not transform:I. PowerII. CurrentIII. FrequencyIV. Voltage
A.	I and II
B.	I and III
C.	II and III
D.	III and IV
Answer» C. II and III

Discussion

178.	Highest rating transformers are likely to find application in
A.	distribution
B.	generation
C.	substation
D.	transmission
Answer» C. substation

Discussion

179.	In the equivalent circuit of transformers the magnetizing circuit branch is drawn in parallel to supply voltage because
A.	transformer has better operational efficiency
B.	transformer has almost equal iron loss and copper loss
C.	transformer’s magnetization current and iron loss remains constant with supply voltage
D.	transformer’s voltage regulation is better
Answer» D. transformer’s voltage regulation is better

Discussion

180.	A distribution transformer is usually a:
A.	star/star transformer
B.	delta/delta transformer
C.	star/delta transformer
D.	delta/star transformer
Answer» E.

Discussion

181.	In an open circuit, a converter of 11 KVA 1100/110 V outputs 100 W of power when 110 V is applied to an LV winding with an open HV winding. If 1100 V is applied on HV winding with open LV winding, what will be the power input?
A.	10000 W
B.	1000 W
C.	100 W
D.	10 W
Answer» D. 10 W

Discussion

182.	A single-phase two winding transformer is designed to operate at 400/200 V, 50 Hz. If the h.v. side is now energized from a 400 V, 40 Hz source, the no-load l.v. side voltage would be
A.	300 V
B.	250 V
C.	200 V
D.	150 V
Answer» D. 150 V

Discussion

183.	If the percentage impedances of the two transformers working in parallel are different then
A.	Transformers will be overheated
B.	Power factors of both the transformers will be same
C.	Parallel operation will not be possible
D.	Parallel operation will still be possible
Answer» E.

Discussion

184.	In a transformer, if the iron losses and copper losses are 40.5 kW and 50 kW respectively, then at what fraction of load will the efficiency be maximum?
A.	0.8
B.	0.57
C.	0.7
D.	0.9
Answer» E.

Discussion

185.	No iron losses means _______ are zero.
A.	only hysteresis losses
B.	only copper losses
C.	hysteresis and eddy current losses
D.	eddy current and copper losses
Answer» D. eddy current and copper losses

Discussion

186.	An open circuit test is performed on 50 Hz transformer, using variable frequency source and keeping V/f ratio constant, to separate its eddy current and hysteresis losses. The variation of core loss/frequency as function of frequency is shown in the figureThe hysteresis and eddy current losses of the transformer at 25 Hz respectively are
A.	250 W and 2.5 W
B.	250 W and 62.5 W
C.	312.5 W and 62.5 W
D.	312.5 W and 250 W
Answer» C. 312.5 W and 62.5 W

Discussion

187.	A transformer is supplying a unity power factor load. Power factor on primary side will be:
A.	About 0.95 lag
B.	unity
C.	About 0.95 lead
D.	zero
Answer» B. unity

Discussion

188.	In an ideal transformer, which of the following statement is correct?
A.	no voltage drops in resistance or leakage reactance
B.	mmf required to maintain main flux is small
C.	no core loss
D.	all the above are correct
Answer» E.

Discussion

189.	In a power transformer, copper losses occur in:
A.	bushing
B.	insulating oil
C.	core
D.	windings
Answer» E.

Discussion

190.	Auto transformer is used in transmission and distribution.
A.	When operater is not available
B.	When iron losses are to be reduced
C.	When efficiency consideration is ignored
D.	When transformation ratio is small
Answer» E.

Discussion

191.	In a transformer having a turns ratio of 1 : 5 and a resistance of 1000 Ω connected across the secondary terminals, the resistance offered to the current flowing in the primary will be:
A.	40 Ω
B.	60 Ω
C.	20 Ω
D.	200 Ω
Answer» B. 60 Ω

Discussion

192.	A transformer having a turn ratio 1 : 5 and a resistance of 1000 ohms is connected across the secondary terminals, the resistance to the current flowing in the primary will be:
A.	10 ohms
B.	20 ohms
C.	40 ohms
D.	60 ohms
Answer» D. 60 ohms

Discussion

193.	Cores of large power transformers are made from which one of the following?
A.	Hot-rolled steel
B.	Cold-rolled non-grain oriented steel
C.	Cold-rolled gain oriented steel
D.	Ferrite
Answer» D. Ferrite

Discussion

194.	If the copper loss of a transformer at half full load is 400 W, then the copper loss corresponding to full load is:
A.	1600 W
B.	800 W
C.	400 W
D.	1200 W
Answer» B. 800 W

Discussion

195.	A 200 kVA, 3300/240 V, 50 Hz single-phase transformer has 80 turns on the secondary winding. Assuming an ideal transformer, the primary current I1 and secondary current I2 on full load are nearly
A.	60.6 A and 833 A
B.	72.2 A and 833 A
C.	60.6 A and 720 A
D.	72.2 A and 720 A
Answer» B. 72.2 A and 833 A

Discussion

196.	During short-circuit test of a transformer, core losses are negligible because
A.	the current on the secondary side is rated current
B.	the voltage on the secondary side is zero
C.	the voltage applied on the primary side is low
D.	full-load current is not supplied to the transformer
Answer» D. full-load current is not supplied to the transformer

Discussion

197.	Consider the following statements concerning the utility of mesh-connected tertiary windings in star-star transformers:1. It is used to suppress harmonic voltages2. It is used to allow flow of earth fault current for operation of protective devices3. It facilitates supply of single-phase loads4. It provides low-reactance paths for zero sequence currentsWhich of these statements are correct?
A.	1, 2, 3, and 4
B.	1, 2 and 3 only
C.	1, 2 and 4 only
D.	3 and 4 only
Answer» B. 1, 2 and 3 only

Discussion

198.	Distribution transformers have core losses:
A.	More than full load copper losses
B.	Equal to full load copper losses
C.	Less than full load copper losses
D.	Negligible compared to full load copper losses
Answer» D. Negligible compared to full load copper losses

Discussion

199.	A transformer is working at full load with maximum efficiency. Its iron loss is 1000 W. What will be its copper loss at half full load?
A.	1000 W
B.	250 W
C.	500 W
D.	2000 W
Answer» C. 500 W

Discussion

200.	A 20 kVA, 2000/200 V, single-phase transformer has a leakage impedance of 8%. What voltage applied to the HV side will result in full-load current flow in the LV side, when the LV side is short-circuited?
A.	64 V
B.	86 V
C.	132 V
D.	160 V
Answer» E.

Discussion

Explore topic-wise MCQs in Transformers.

A 10 kVA 500/100 V transformer has the resistance referred to primary is 0.3 Ω. The equivalent resistance of transformer referred to secondary is:

Find primary turns of a 444 V/222 V, 50 Hz single-phase transformer with a core cross-sectional area of 100 cm2, and a maximum flux density of 1.0 T?

In a transformer, _________ losses are reduced by decreasing the thickness of lamination of magnetic core and yoke.

Breather is provided in a transformer to

A 4 kVA transformer has iron-loss of 200 W and full load copper loss of 200 W. The maximum efficiency at unity power factor will be

A dc voltage supply provides 60 V when the output is unloaded. When connected to a load, the output voltage drops to 56 V. The value of the voltage regulation is

Power loss in a transformer is known as the _____.

A single-phase, \(22\;kVA,\;2200\;V/\;220\;V,\;50\;Hz\), distribution transformer is to be connected as an auto-transformer to get an output voltage of \(2420\;V\). Its maximum \(kVA\)​ rating as an auto-transformer is

Distribution transformers are designed to have maximum efficiency nearly at:

In a Scott-connected transformer the number of primary and teaser turns respectively are ____

Core lamination in a transformer decreases _______.

A 100 VA, 120/12 V transformer is to be connected so as to form a step-up transformer. A Primary voltage of 120 V is applied to the transformer. What is the secondary voltage of the transformer?

A 20 turns iron cored inductor is connected to a 100 V, 50 Hz source. The maximum flux density in the core is 1 wb/m2. The cross-sectional area of the core in the transformer is

On the two sides of a star/delta transformer ________

Hysteresis loss can be minimized by selecting a material for the core that has:

During the short circuit test on a small transformer, the frequency is increased from 50 Hz to 200 Hz, the copper losses will decrease by a factor of:

A transformer operates most efficiently at 3/4th full load. Its iron loss (Pi) and full load copper loss (Pc) are related as

A 2000/200 V, 50 Hz single-phase transformer has an exciting current of 0.5 A and a core-loss of 600 W. When H.V side is energized by the rate voltage and frequency, the magnetizing current is

A 1-ϕ transformer has total iron losses of 2500 W at 50 Hz and 400 V input supply voltage. When the applied voltage is 200 V and supply frequency is 25 Hz, the total iron loss is found to be 850 W. Calculate the eddy current loss at 400 V 50 Hz. (Consider V/f ratio as constant)

A saturable core reactor is basically a

In a transformer operating at a constant voltage, if the input frequency increases, the core loss:

A transformer has a core loss of 140 W at 40 Hz, and 99 W at 30 Hz. The hysteresis and eddy-current losses at 50 Hz, respectively, are

If the pu impedance of a single-phase transformer is 0.01 + j0.05, then its regulation at p.f. of 0.8 lagging will be ______.​

In a transformer the core loss is 100 Watt at 40 Hz and 72 Watt at 30 Hz, then eddy current and hysteresis losses at 50 Hz respectively are

Calculate the regulation of the transformer in which ohmic loss is 1% of the output and reactance drop is 5% of the voltage when the power factor is 0.8 lag

An ideal transformer will not transform:I. PowerII. CurrentIII. FrequencyIV. Voltage

Highest rating transformers are likely to find application in

In the equivalent circuit of transformers the magnetizing circuit branch is drawn in parallel to supply voltage because

A distribution transformer is usually a:

In an open circuit, a converter of 11 KVA 1100/110 V outputs 100 W of power when 110 V is applied to an LV winding with an open HV winding. If 1100 V is applied on HV winding with open LV winding, what will be the power input?

A single-phase two winding transformer is designed to operate at 400/200 V, 50 Hz. If the h.v. side is now energized from a 400 V, 40 Hz source, the no-load l.v. side voltage would be

If the percentage impedances of the two transformers working in parallel are different then

In a transformer, if the iron losses and copper losses are 40.5 kW and 50 kW respectively, then at what fraction of load will the efficiency be maximum?

No iron losses means _______ are zero.

A transformer is supplying a unity power factor load. Power factor on primary side will be:

In an ideal transformer, which of the following statement is correct?

In a power transformer, copper losses occur in:

Auto transformer is used in transmission and distribution.

In a transformer having a turns ratio of 1 : 5 and a resistance of 1000 Ω connected across the secondary terminals, the resistance offered to the current flowing in the primary will be:

A transformer having a turn ratio 1 : 5 and a resistance of 1000 ohms is connected across the secondary terminals, the resistance to the current flowing in the primary will be:

Cores of large power transformers are made from which one of the following?

If the copper loss of a transformer at half full load is 400 W, then the copper loss corresponding to full load is:

A 200 kVA, 3300/240 V, 50 Hz single-phase transformer has 80 turns on the secondary winding. Assuming an ideal transformer, the primary current I1 and secondary current I2 on full load are nearly

During short-circuit test of a transformer, core losses are negligible because

Distribution transformers have core losses:

A transformer is working at full load with maximum efficiency. Its iron loss is 1000 W. What will be its copper loss at half full load?

A 20 kVA, 2000/200 V, single-phase transformer has a leakage impedance of 8%. What voltage applied to the HV side will result in full-load current flow in the LV side, when the LV side is short-circuited?

A single-phase, \(22\;kVA,\;2200\;V/\;220\;V,\;50\;Hz\), distribution transformer is to be connected as an auto-transformer to get an output voltage of \(2420\;V\). Its maximum \(kVA\) rating as an auto-transformer is

If the pu impedance of a single-phase transformer is 0.01 + j0.05, then its regulation at p.f. of 0.8 lagging will be ______.