For power transformer of larger ratings, the tapping’s are located in the middle portion of the winding to

Increase the break-down strength of the winding insulation

Enable better cooling of the windings

Enable better distribution of inter-turn voltage

Reduce the mechanical force affecting the winding during short-circuits.

Eddy current loss of a transformer is

Directly proportional to resistivity of core material

Directly proportional to square of resistivity of core material

Inversely proportional to square of resistivity of core material

Inversely proportional to resistivity of core material

A tap changer is used on a transformer for adjustments in

Both primary and secondary voltages

Neither primary nor secondary voltages

In parallel operation of 1-ϕ transformers, a dead short circuit can happen if:

their percentage impedances are not equal

there is a difference in the transformation ratios of the transformers

the power factors of transformer don't match with that of the load

paralleling is done with incorrect polarities

In order to achieve all day efficiency in a transformer

The copper losses should be less

The operating temperature should be low

The shell type construction should be used

In a transformer, the load component of a primary current may be calculated as:

\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{N}}_1}}}{{{{\rm{N}}_2}}}} \right) \times {{\rm{I}}_2}\)

\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{I}}_1}}}{{{{\rm{I}}_2}}}} \right) \times {{\rm{I}}_2}\)

\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{V}}_1}}}{{{{\rm{V}}_2}}}} \right) \times {{\rm{I}}_2}\)

\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{N}}_2}}}{{{{\rm{N}}_1}}}} \right) \times {{\rm{I}}_2}\)

In transformer, zero voltage regulation at full load is

Possible at lagging power factor load

Possible at unity power factor load

Possible at leading power factor load

Possible at lagging power factor load

Iron losses in a transformer is a sum of:

copper loss, eddy current loss and hysteresis loss

copper loss and hysteresis loss

hysteresis loss and eddy current loss

copper loss, eddy current loss and hysteresis loss

During the short-circuit test, the iron loss of a transformer is negligible because of ________.

iron core becomes fully saturated

the entire input is just sufficient to meet copper losses only

the voltage applied across the HV (High Voltage) side is a small fraction of the rated voltage and so its flux

iron core becomes fully saturated

supply frequency is held constant

Hysteresis loss (Ph) is computed using the equation

\({P_h} = {K_h}B_m^{1.6}{f^{1.6}}\)

In the case of an ideal transformer, the primary supply voltage and current are:

mutually perpendicular to each other

at ‘Ø’ degrees with each other, where 0 < Ø < 90°

Leakage flux in a transformer _______.

helps in the transfer of energy

is minimised by interleaving the primary and secondary windings

If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, when

both hysteresis loss and eddy current loss in the core will increase

hysteresis loss will increase but eddy current loss in the core will decrease

hysteresis loss will decrease but eddy current loss will increase

hysteresis loss will decrease but eddy current loss will remain unchanged

A one-phase, 50 Hz core type transformer has core of cross-section 400 cm2. The permissible maximum B = 1 T, Find the number of turns on high and low voltage sides for a 3000 V/220 V ratio.

Nlv = 48 turns, Nhv = 654 turns

Nlv = 338 turns, Nhv = 25 turns

Nlv = 25 turns, Nhv = 338 turns

Nlv = 48 turns, Nhv = 654 turns

Nlv = 35 turns, Nhv = 477 turns

Open-circuit test of a transformer gives

insulation losses in the transformer

copper losses in the transformer

insulation losses in the transformer

hysteresis losses in the transformer

In a 1-phase transformer the emf per turn of secondary side is:

1/4 the emf per turn of primary side

Same as emf per turn of primary side

1/4 the emf per turn of primary side

3/4 the emf per turn of primary side

Half the emf per turn of primary side

Per unit impedances of transformer, measured from primary side and secondary side are

depends on rating on transformer

depends on polarity of windings

If a transformer is designed for maximum efficiency at rated current and voltage, the full-load copper loss will be

Not definable by these given parameters

much greater than the core loss

Not definable by these given parameters

For a two – winding power transformer, with the effects of the no – load current being neglected, the ‘Voltage Regulation’ can be zero at load, when the load power factor is

Either lagging or leading, depending upon power rating of the transformer

Losses which do not occur in transformer but do occur in rotating electric machine are

Hysteresis and eddy current losses

In context of a three phase transformer, what is the angle difference between the phase voltages in primary and secondary sides if the primary side is connected in star and secondary side is connected in delta connection?

Star side leads by +/- 113 degree

Delta side lags by +/- 130 degree

Star side lags by +/- 145 degree

delta side leads by +/- 30 degree

Star side leads by +/- 113 degree

293 + Mcqs in Ideal Transformer in Transformers Page 3 McqOptions

101.	In a transformer zero voltage regulation at full load can happen
A.	At leading power factor load
B.	At lagging power factor load
C.	At unity power factor load
D.	Can not happen at all
Answer» B. At lagging power factor load

Discussion

102.	For power transformer of larger ratings, the tapping’s are located in the middle portion of the winding to
A.	Increase the break-down strength of the winding insulation
B.	Enable better cooling of the windings
C.	Enable better distribution of inter-turn voltage
D.	Reduce the mechanical force affecting the winding during short-circuits.
Answer» E.

Discussion

103.	Eddy current loss of a transformer is
A.	Directly proportional to resistivity of core material
B.	Directly proportional to square of resistivity of core material
C.	Inversely proportional to square of resistivity of core material
D.	Inversely proportional to resistivity of core material
Answer» E.

Discussion

104.	After absorbing moisture from the air, the colour of the silica gel will be ____________.
A.	Blue
B.	Red
C.	Purple
D.	Light pink
Answer» E.

Discussion

105.	Load sharing in parallel operation by transformer is according to __________.
A.	Voltage
B.	Inductance
C.	Current
D.	kVA rating
Answer» E.

Discussion

106.	In a transformer, primary has 200 turns and secondary has 50 turns. If 240 V AC is applied in the primary, what is the voltage in the secondary?
A.	960 V
B.	60 V
C.	80 V
D.	240 V
Answer» C. 80 V

Discussion

107.	A 100 MVA single phase transformer rated 80/120 kV is connected as an auto transformer in such a way that the doted terminal of LV side is connected to the un-doted terminal of HV side. Un-doted terminal of LV side is taken as common for both LV and HV. The rated voltage of 80 kV is applied to the low voltage winding of the transformer. Consider the transformer to be ideal and load to be such that the rated current flows through both primary and secondary windings. What is the kVA rating of the autotransformer?
A.	200 MVA
B.	250 MVA
C.	172 MVA
D.	167 MVA
Answer» E.

Discussion

108.	For a single phase, two winding transformer, the supply frequency and voltage are both increased by 10%. The percentage changes in the hysteresis loss and eddy current loss, respectively, are
A.	10 and 21
B.	-10 and 21
C.	21 and 10
D.	-21 and 10
Answer» B. -10 and 21

Discussion

109.	A tap changer is used on a transformer for adjustments in
A.	Primary voltage
B.	Secondary voltage
C.	Both primary and secondary voltages
D.	Neither primary nor secondary voltages
Answer» C. Both primary and secondary voltages

Discussion

110.	In parallel operation of 1-ϕ transformers, a dead short circuit can happen if:
A.	their percentage impedances are not equal
B.	there is a difference in the transformation ratios of the transformers
C.	the power factors of transformer don't match with that of the load
D.	paralleling is done with incorrect polarities
Answer» E.

Discussion

111.	From an open circuit test on a transformer, the no-load power factor was determined. Out of the following choices which is the most likely value.
A.	0.9
B.	unity
C.	0.8
D.	0.4
Answer» E.

Discussion

112.	In order to achieve all day efficiency in a transformer
A.	The copper losses should be less
B.	The operating temperature should be low
C.	The shell type construction should be used
D.	The iron losses should be less
Answer» E.

Discussion

113.	A transformer has 1000 primary turns. It is connected to 250 volts A.C. supply. Find the number of secondary turns to get secondary voltage of 400 volts.
A.	1600
B.	625
C.	100
D.	1250
Answer» B. 625

Discussion

114.	Power input to a transformer on no-load at rated voltage comprises predominantly of
A.	Copper loss
B.	Hysteresis loss
C.	Core loss
D.	Eddy current loss
Answer» D. Eddy current loss

Discussion

115.	A transformer has an iron loss of 900 W and copper loss of 1600 W at full load. At what percentage of the load will be the efficiency be maximum?
A.	133
B.	125
C.	75
D.	66.66
Answer» D. 66.66

Discussion

116.	In a transformer, what is the phasor relationship of the loss component of no-load current with the mutual flux?
A.	Out of phase with the flux
B.	Lags flux by 90°
C.	Leads flux by 90°
D.	In phase with the flux
Answer» D. In phase with the flux

Discussion

117.	In a transformer, the load component of a primary current may be calculated as:
A.	\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{N}}_1}}}{{{{\rm{N}}_2}}}} \right) \times {{\rm{I}}_2}\)
B.	\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{I}}_1}}}{{{{\rm{I}}_2}}}} \right) \times {{\rm{I}}_2}\)
C.	\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{V}}_1}}}{{{{\rm{V}}_2}}}} \right) \times {{\rm{I}}_2}\)
D.	\({\rm{I}}_1^{\rm{'}} = \left( {\frac{{{{\rm{N}}_2}}}{{{{\rm{N}}_1}}}} \right) \times {{\rm{I}}_2}\)
Answer» E.

Discussion

118.	In transformer, zero voltage regulation at full load is
A.	Not possible
B.	Possible at unity power factor load
C.	Possible at leading power factor load
D.	Possible at lagging power factor load
Answer» D. Possible at lagging power factor load

Discussion

119.	Iron losses in a transformer is a sum of:
A.	copper loss and hysteresis loss
B.	constant loss and copper loss
C.	hysteresis loss and eddy current loss
D.	copper loss, eddy current loss and hysteresis loss
Answer» D. copper loss, eddy current loss and hysteresis loss

Discussion

120.	A 200/100 V 50 Hz transformer is to be excited at 60 Hz from the primary side without increase in magnetizing current. Then the voltage applied at primary is
A.	160 V
B.	200 V
C.	240 V
D.	280 V
Answer» D. 280 V

Discussion

121.	A 4000 V/2000 V, 60 Hz single phase transformer has a total impedance of 60 Ω referred to the primary side. The primary and secondary windings have negligible resistances. If the transformer supplies a resistive of 20 Ω, the full load voltage at the secondary side will be
A.	1143 V
B.	1600 V
C.	2000 V
D.	3200 V
Answer» B. 1600 V

Discussion

122.	During the short-circuit test, the iron loss of a transformer is negligible because of ________.
A.	the entire input is just sufficient to meet copper losses only
B.	the voltage applied across the HV (High Voltage) side is a small fraction of the rated voltage and so its flux
C.	iron core becomes fully saturated
D.	supply frequency is held constant
Answer» C. iron core becomes fully saturated

Discussion

123.	A 1600 kVA, 200 Hz transformer is operated at 50 Hz. Its kVA rating should be restricted to
A.	800
B.	400
C.	200
D.	100
Answer» C. 200

Discussion

124.	If the iron core of a transformer is replaced by an air core, then the hysteresis losses in the transformer will
A.	Increase
B.	Decrease
C.	Remains unchanged
D.	Become zero
Answer» E.

Discussion

125.	Hysteresis loss (Ph) is computed using the equation
A.	\({P_h} = K_h^{1.6}Bf\)
B.	\({P_h} = {K_h}B_m^{1.6}f\)
C.	\({P_h} = {K_h}B{f^{1.6}}\)
D.	\({P_h} = {K_h}B_m^{1.6}{f^{1.6}}\)
Answer» C. \({P_h} = {K_h}B{f^{1.6}}\)

Discussion

126.	In the case of an ideal transformer, the primary supply voltage and current are:
A.	in phase with each other
B.	mutually perpendicular to each other
C.	out of phase with each other
D.	at ‘Ø’ degrees with each other, where 0 < Ø < 90°
Answer» C. out of phase with each other

Discussion

127.	A 100 kVA, single-phase transformer has a full-load copper loss of 600 W and iron loss of 500 W. The maximum efficiency occurs at a load of nearly
A.	82.1 kVA
B.	83.3 kVA
C.	91.3 kVA
D.	98.1 kVA
Answer» D. 98.1 kVA

Discussion

128.	Input of a transformer is square wave, then the output will be_________.
A.	Pulsed wave
B.	Square wave
C.	Triangular wave
D.	Sine wave
Answer» B. Square wave

Discussion

129.	A 100 kVA, 6600/400 V, 50 Hz single phase transformer has 80 turns on LV side. At 25 Hz its flux increases by 10%. The HV and kVA rating at 25 Hz will be respectively.
A.	3630 V, 55 kVA
B.	6600 V, 100 kVA
C.	7260 V, 100 kVA
D.	6600 V, 55 kVA
Answer» B. 6600 V, 100 kVA

Discussion

130.	Efficiency of a power transformer is in the order of
A.	60%
B.	70%
C.	80%
D.	97%
Answer» E.

Discussion

131.	Leakage flux in a transformer _______.
A.	helps in the transfer of energy
B.	produces mutually-induced emf
C.	is minimised by interleaving the primary and secondary windings
D.	is negligible at full load
Answer» D. is negligible at full load

Discussion

132.	If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, when
A.	both hysteresis loss and eddy current loss in the core will increase
B.	hysteresis loss will increase but eddy current loss in the core will decrease
C.	hysteresis loss will decrease but eddy current loss will increase
D.	hysteresis loss will decrease but eddy current loss will remain unchanged
Answer» E.

Discussion

133.	On which of the following do the eddy current losses depend ?I. Nature of the materialll. Maximum flux densityIll. FrequencyChoose the correct answer from the options given below.
A.	I, II and III
B.	II and III
C.	I and II
D.	I and III
Answer» B. II and III

Discussion

134.	A one-phase, 50 Hz core type transformer has core of cross-section 400 cm2. The permissible maximum B = 1 T, Find the number of turns on high and low voltage sides for a 3000 V/220 V ratio.
A.	Nlv = 338 turns, Nhv = 25 turns
B.	Nlv = 25 turns, Nhv = 338 turns
C.	Nlv = 48 turns, Nhv = 654 turns
D.	Nlv = 35 turns, Nhv = 477 turns
Answer» C. Nlv = 48 turns, Nhv = 654 turns

Discussion

135.	A 2 kVA transformer has iron loss of 150 W and full load copper loss of 250 W. The maximum efficiency of the transformer will occur when the total loss is:
A.	500 W
B.	400 W
C.	300 W
D.	275 W
Answer» D. 275 W

Discussion

136.	Open-circuit test of a transformer gives
A.	copper losses in the transformer
B.	iron-losses in the transformer
C.	insulation losses in the transformer
D.	hysteresis losses in the transformer
Answer» C. insulation losses in the transformer

Discussion

137.	In a 1-phase transformer the emf per turn of secondary side is:
A.	Same as emf per turn of primary side
B.	1/4 the emf per turn of primary side
C.	3/4 the emf per turn of primary side
D.	Half the emf per turn of primary side
Answer» B. 1/4 the emf per turn of primary side

Discussion

138.	In Scott connection, if the turn’s ratio of main transformer is K, then the teaser transformer has turn ratio of
A.	\(\frac{{2K}}{{\sqrt 3 }}\)
B.	\(\frac{{\sqrt 3 }}{2}K\)
C.	\(\frac{K}{{\sqrt 3 }}\)
D.	\(\frac{K}{2}\)
Answer» C. \(\frac{K}{{\sqrt 3 }}\)

Discussion

139.	A dc motor running at 2000 rpm has a hysteresis loss of 500 W and eddy-current loss of 200 W. The flux is maintained constant, but the speed is reduced to 1000 rpm. At the reduced speed the total iron-loss would be
A.	500 W
B.	400 W
C.	300 W
D.	200 W
Answer» D. 200 W

Discussion

140.	Per unit impedances of transformer, measured from primary side and secondary side are
A.	equal
B.	depends on transformer ratio
C.	depends on rating on transformer
D.	depends on polarity of windings
Answer» B. depends on transformer ratio

Discussion

141.	A 50 kVA, 1000/200 V transformer takes 5 A current at a power factor of 0.2 lagging, when connected to 1000 V side at no load is connected at the other side. The core loss in transformer will be:
A.	1000 W
B.	500 W
C.	2000 W
D.	2200 W
Answer» B. 500 W

Discussion

142.	A 3 phase transformer has its primary connected in delta and secondary in star. Secondary to primary turns ratio per phase is 5. What would be the secondary voltage for a primary voltage of 400 V?
A.	3464 V
B.	80 V
C.	2000 V
D.	138 V
Answer» B. 80 V

Discussion

143.	If a transformer is designed for maximum efficiency at rated current and voltage, the full-load copper loss will be
A.	much less than the core loss
B.	much greater than the core loss
C.	equal to the core loss
D.	Not definable by these given parameters
Answer» D. Not definable by these given parameters

Discussion

144.	For a two – winding power transformer, with the effects of the no – load current being neglected, the ‘Voltage Regulation’ can be zero at load, when the load power factor is
A.	Lagging only
B.	Leading only
C.	Either lagging or leading, depending upon power rating of the transformer
D.	unity
Answer» C. Either lagging or leading, depending upon power rating of the transformer

Discussion

145.	lf in a transformer, 'PM' denotes the maximum value of the flux, 'f' is the frequency of the supply voltage, 'N1' is number of primary winding turns, 'E1' is RMS value of the primary induced emf, then one of the equations of the transformer would be:
A.	E1 = 4.44 f PM N1
B.	E1 = 2.35 f PM N1
C.	E1 = 1.23 f PM N1
D.	E1 = 7.8 f PM N1
Answer» B. E1 = 2.35 f PM N1

Discussion

146.	An ideal transformer has:
A.	very high losses
B.	very low losses
C.	moderate losses
D.	no losses
Answer» E.

Discussion

147.	In an oil-filled transformer, oil is used as
A.	Cooling agent
B.	Insulating agent
C.	Vibration isolator
D.	None of the above
Answer» B. Insulating agent

Discussion

148.	A one-phase transformer has 400 and 1000 turns in primary and secondary, respectively. The cross-sectional area of the core is 60 cm2. The primary of the transformer is connected to a supply of one-phase, 50 Hz, 500 V. Determine the secondary voltage of the transformer.
A.	800 V
B.	1250 V
C.	125 V
D.	8000 V
Answer» C. 125 V

Discussion

149.	Losses which do not occur in transformer but do occur in rotating electric machine are
A.	Copper losses
B.	Magnetic losses
C.	Friction and windage losses
D.	Hysteresis and eddy current losses
Answer» D. Hysteresis and eddy current losses

Discussion

150.	In context of a three phase transformer, what is the angle difference between the phase voltages in primary and secondary sides if the primary side is connected in star and secondary side is connected in delta connection?
A.	Delta side lags by +/- 130 degree
B.	Star side lags by +/- 145 degree
C.	delta side leads by +/- 30 degree
D.	Star side leads by +/- 113 degree
Answer» D. Star side leads by +/- 113 degree

Discussion

Explore topic-wise MCQs in Transformers.

In a transformer zero voltage regulation at full load can happen

For power transformer of larger ratings, the tapping’s are located in the middle portion of the winding to

Eddy current loss of a transformer is

After absorbing moisture from the air, the colour of the silica gel will be ____________.

Load sharing in parallel operation by transformer is according to __________.

In a transformer, primary has 200 turns and secondary has 50 turns. If 240 V AC is applied in the primary, what is the voltage in the secondary?

For a single phase, two winding transformer, the supply frequency and voltage are both increased by 10%. The percentage changes in the hysteresis loss and eddy current loss, respectively, are

A tap changer is used on a transformer for adjustments in

In parallel operation of 1-ϕ transformers, a dead short circuit can happen if:

From an open circuit test on a transformer, the no-load power factor was determined. Out of the following choices which is the most likely value.

In order to achieve all day efficiency in a transformer

A transformer has 1000 primary turns. It is connected to 250 volts A.C. supply. Find the number of secondary turns to get secondary voltage of 400 volts.

Power input to a transformer on no-load at rated voltage comprises predominantly of

A transformer has an iron loss of 900 W and copper loss of 1600 W at full load. At what percentage of the load will be the efficiency be maximum?

In a transformer, what is the phasor relationship of the loss component of no-load current with the mutual flux?

In a transformer, the load component of a primary current may be calculated as:

In transformer, zero voltage regulation at full load is

Iron losses in a transformer is a sum of:

A 200/100 V 50 Hz transformer is to be excited at 60 Hz from the primary side without increase in magnetizing current. Then the voltage applied at primary is

A 4000 V/2000 V, 60 Hz single phase transformer has a total impedance of 60 Ω referred to the primary side. The primary and secondary windings have negligible resistances. If the transformer supplies a resistive of 20 Ω, the full load voltage at the secondary side will be

During the short-circuit test, the iron loss of a transformer is negligible because of ________.

A 1600 kVA, 200 Hz transformer is operated at 50 Hz. Its kVA rating should be restricted to

If the iron core of a transformer is replaced by an air core, then the hysteresis losses in the transformer will

Hysteresis loss (Ph) is computed using the equation

In the case of an ideal transformer, the primary supply voltage and current are:

A 100 kVA, single-phase transformer has a full-load copper loss of 600 W and iron loss of 500 W. The maximum efficiency occurs at a load of nearly

Input of a transformer is square wave, then the output will be_________.

A 100 kVA, 6600/400 V, 50 Hz single phase transformer has 80 turns on LV side. At 25 Hz its flux increases by 10%. The HV and kVA rating at 25 Hz will be respectively.

Efficiency of a power transformer is in the order of

Leakage flux in a transformer _______.

If the frequency of input voltage of a transformer is increased keeping the magnitude of voltage unchanged, when

On which of the following do the eddy current losses depend ?I. Nature of the materialll. Maximum flux densityIll. FrequencyChoose the correct answer from the options given below.

A one-phase, 50 Hz core type transformer has core of cross-section 400 cm2. The permissible maximum B = 1 T, Find the number of turns on high and low voltage sides for a 3000 V/220 V ratio.

A 2 kVA transformer has iron loss of 150 W and full load copper loss of 250 W. The maximum efficiency of the transformer will occur when the total loss is:

Open-circuit test of a transformer gives

In a 1-phase transformer the emf per turn of secondary side is:

In Scott connection, if the turn’s ratio of main transformer is K, then the teaser transformer has turn ratio of

A dc motor running at 2000 rpm has a hysteresis loss of 500 W and eddy-current loss of 200 W. The flux is maintained constant, but the speed is reduced to 1000 rpm. At the reduced speed the total iron-loss would be

Per unit impedances of transformer, measured from primary side and secondary side are

A 50 kVA, 1000/200 V transformer takes 5 A current at a power factor of 0.2 lagging, when connected to 1000 V side at no load is connected at the other side. The core loss in transformer will be:

A 3 phase transformer has its primary connected in delta and secondary in star. Secondary to primary turns ratio per phase is 5. What would be the secondary voltage for a primary voltage of 400 V?

If a transformer is designed for maximum efficiency at rated current and voltage, the full-load copper loss will be

For a two – winding power transformer, with the effects of the no – load current being neglected, the ‘Voltage Regulation’ can be zero at load, when the load power factor is

lf in a transformer, 'PM' denotes the maximum value of the flux, 'f' is the frequency of the supply voltage, 'N1' is number of primary winding turns, 'E1' is RMS value of the primary induced emf, then one of the equations of the transformer would be:

An ideal transformer has:

In an oil-filled transformer, oil is used as

A one-phase transformer has 400 and 1000 turns in primary and secondary, respectively. The cross-sectional area of the core is 60 cm2. The primary of the transformer is connected to a supply of one-phase, 50 Hz, 500 V. Determine the secondary voltage of the transformer.

Losses which do not occur in transformer but do occur in rotating electric machine are

In context of a three phase transformer, what is the angle difference between the phase voltages in primary and secondary sides if the primary side is connected in star and secondary side is connected in delta connection?