In a full bridge single phase inverter feeding RLC load

four thyristors conduct simultaneously

one thyristor and one diode conduct simultaneously

two thyristors conduct simultaneously

two thyristors or two diodes conduct simultaneously

four thyristors conduct simultaneously

A single phase half wave rectifier circuit has a free wheeling diode. The free wheeling diode will conduct only if

load is purely inductive or combination of R and L

both firing and turning off an SCR

Assertion (A): A high dv/dt may cause triggering of a thyristor.Reason (R): A high dv/dt results in charging current in the thyristor.

Both A and R correct but R is not correct explanation of A

Both A and R are correct and R is correct explanation of A

Both A and R correct but R is not correct explanation of A

A cycloconverter for single phase operation has

two positive group and two negative group converters

one positive group and one negative group converters

two positive group and two negative group converters

three positive group and three negative group converters

In the basic series inverter circuit, the source current has

low or high harmonic content depending on firing angle

A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load

rectification efficiency will be more than 0.6 but TUF will be less than 0.35

rectification efficiency will be more than 0.6 and TUF will be more than 0.35

rectification efficiency will be more than 0.6 but TUF will be less than 0.35

rectification efficiency will be less than 0.6 and TUF will be less than 0.35

rectification efficiency will be less than 0.6 but TUF will be more than 0.35

In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be

more than the mechanical or thermal time constant of the system

less than mechanical or thermal time constant of the system

more than the mechanical or thermal time constant of the system

more or less than the mechanical or thermal time constant

In thermal ohm's law, temperature and power loss are analogous to

R and V respectively of ohm's law

V and I respectively of ohm's law

I and V respectively of ohm's law

R and V respectively of ohm's law

I and R respectively of ohm's law

A UJT exhibits negative resistance characteristics when

Current is less than valley current

Current is less than peak current

Current is more than peak current but less than valley current

Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off time.

Both A and R correct but R is not correct explanation of A

Both A and R are correct and R is correct explanation of A

Both A and R correct but R is not correct explanation of A

Assertion (A): The output voltage of an inverter can be controlled by PWM techniqueReason (R): In a current source inverter the input current is constant.

Both A and R are correct and R is correct explanation of A

Both A and R correct but R is not correct explanation of A

In a thyristor the gate current is increased, then

anode current may increase or decrease

anode current will remain constant

anode current may increase or decrease

A high frequency series inverter consists of

a number of parallel inverters in parallel

a number of series inverters in series

a number of series inverters in parallel

a number of parallel inverters in parallel

a number of parallel inverters in series

In auxiliary commutated chopper, the peak value of thyristor current is

equal to peak value of load current

equal to peak value of capacitor current

sum of peak value of load current and capacitor current

The gate lead, in a thyristor is welded to :

p layer nearest to the cathode terminal

p layer to which anode is connected

n layer nearest to the anode terminal

p layer nearest to the cathode terminal

converts ac of one frequency into ac of another frequency

converts constant voltage dc into ac and then into variable voltage dc

converts constant voltage dc into variable voltage dc directly

converts ac of one frequency into ac of another frequency

SCR and avalanche diode connected in parallel

exactly similar to SCR but with higher rating

PUT and avalanche diode connected in anti parallel

SCR and avalanche diode connected in parallel

Two thyristors of the same rating and specifications

will have equal on state voltage drops

will have equal forward blocking voltage for the same current

will have different on state voltage drops

may have equal or different on state voltage drops and equal or different forward blocking voltage's for the same current

Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C.

Both A and R are correct and R is correct explanation of A

Both A and R correct but R is not correct explanation of A

451 + Mcqs in Power Electronics and Drives in ENGINEERING SERVICES EXAMINATION (ESE) Page 2 McqOptions

51.	In a full bridge single phase inverter feeding RLC load
A.	one thyristor and one diode conduct simultaneously
B.	two thyristors conduct simultaneously
C.	two thyristors or two diodes conduct simultaneously
D.	four thyristors conduct simultaneously
Answer» D. four thyristors conduct simultaneously

Discussion

52.	A single phase half wave rectifier circuit has a free wheeling diode. The free wheeling diode will conduct only if
A.	load is purely resistive
B.	load is purely inductive
C.	load is combination of R and L
D.	load is purely inductive or combination of R and L
Answer» E.

Discussion

53.	UJT can be used for
A.	firing an SCR
B.	turning off an SCR
C.	both firing and turning off an SCR
D.	none of the above
Answer» B. turning off an SCR

Discussion

54.	The specified maximum junction temperature of thyristors is about
A.	50°C
B.	80°C
C.	120°C
D.	200°C
Answer» D. 200°C

Discussion

55.	In sinusoidal PWM for inverters the width of different pulses are not the same.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

56.	Assertion (A): A high dv/dt may cause triggering of a thyristor.Reason (R): A high dv/dt results in charging current in the thyristor.
A.	Both A and R are correct and R is correct explanation of A
B.	Both A and R correct but R is not correct explanation of A
C.	A is correct but R is wrong
D.	A is wrong but R is correct
Answer» B. Both A and R correct but R is not correct explanation of A

Discussion

57.	A cycloconverter cannot give a frequency higher than input frequency.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» C. May be True or False

Discussion

58.	The number of leads in an SCR are :
A.	2
B.	3
C.	4
D.	5
Answer» C. 4

Discussion

59.	A cycloconverter for single phase operation has
A.	one positive group and one negative group converters
B.	two positive group and two negative group converters
C.	three positive group and three negative group converters
D.	any of the above
Answer» B. two positive group and two negative group converters

Discussion

60.	A single phase semiconverter has a freewheeling diode. If the firing angle is α and the load is purely resistive, the periods of conduction and freewheeling respectively are
A.	π - α and 0
B.	π - α and α
C.	π + α and 0
D.	π + α and α
Answer» B. π - α and α

Discussion

61.	A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be
A.	about 1350 rpm
B.	about 720 rpm
C.	about 360 rpm
D.	either (b) or (c)
Answer» C. about 360 rpm

Discussion

62.	A cycloconverter is a group of controlled rectifiers.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» B. False

Discussion

63.	In the basic series inverter circuit, the source current has
A.	low harmonic content
B.	high harmonic content
C.	low or high harmonic content depending on firing angle
D.	zero harmonic content
Answer» C. low or high harmonic content depending on firing angle

Discussion

64.	A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load
A.	rectification efficiency will be more than 0.6 and TUF will be more than 0.35
B.	rectification efficiency will be more than 0.6 but TUF will be less than 0.35
C.	rectification efficiency will be less than 0.6 and TUF will be less than 0.35
D.	rectification efficiency will be less than 0.6 but TUF will be more than 0.35
Answer» B. rectification efficiency will be more than 0.6 but TUF will be less than 0.35

Discussion

65.	On load tap changer using thyristors can have a maximum of two taps.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» C. May be True or False

Discussion

66.	In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be
A.	less than mechanical or thermal time constant of the system
B.	more than the mechanical or thermal time constant of the system
C.	more or less than the mechanical or thermal time constant
D.	very high
Answer» B. more than the mechanical or thermal time constant of the system

Discussion

67.	A single phase semiconverter is supplying RLE load and has a freewheeling diode across the load. The firing angle is α. The freewheeling diode conducts for
A.	α° in each half cycle
B.	(π - α)° in each cycle
C.	α° in one full cycle
D.	(π + α)° in each half cycle
Answer» B. (π - α)° in each cycle

Discussion

68.	Which of the following devices has metal-silicon junction?
A.	General purpose power diode
B.	Schottky diode
C.	SCR
D.	MOSFET
Answer» C. SCR

Discussion

69.	In thermal ohm's law, temperature and power loss are analogous to
A.	V and I respectively of ohm's law
B.	I and V respectively of ohm's law
C.	R and V respectively of ohm's law
D.	I and R respectively of ohm's law
Answer» C. R and V respectively of ohm's law

Discussion

70.	Mc Murray full bridge inverter uses
A.	4 thyristors and 2 diodes
B.	4 thyristors and 4 diodes
C.	8 thyristors and 4 diodes
D.	8 thyristors and 8 diodes
Answer» D. 8 thyristors and 8 diodes

Discussion

71.	Which of these commutation methods uses an auxiliary SCR?
A.	Class A
B.	Class B
C.	Class C
D.	Class D
Answer» D. Class D

Discussion

72.	A separately excited dc motor is run from a dc source through a chopper. At 600 rpm and rated torque, the duty cycle of chopper is 0.8. At 600 rpm and half the rated torque, the duty cycle is likely to be
A.	0.9
B.	0.8
C.	0.75
D.	0.6
Answer» D. 0.6

Discussion

73.	A UJT exhibits negative resistance characteristics when
A.	Current is less than valley current
B.	Current is less than peak current
C.	Current is more than peak current but less than valley current
D.	None of the above
Answer» D. None of the above

Discussion

74.	Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off time.
A.	Both A and R are correct and R is correct explanation of A
B.	Both A and R correct but R is not correct explanation of A
C.	A is correct but R is wrong
D.	A is wrong but R is correct
Answer» B. Both A and R correct but R is not correct explanation of A

Discussion

75.	In single phase half wave regulator, the average current over one full cycle
A.	is always positive
B.	may be positive or negative
C.	may be negative
D.	is always negative
Answer» E.

Discussion

76.	Assertion (A): The output voltage of an inverter can be controlled by PWM techniqueReason (R): In a current source inverter the input current is constant.
A.	Both A and R are correct and R is correct explanation of A
B.	Both A and R correct but R is not correct explanation of A
C.	A is correct but R is wrong
D.	A is wrong but R is correct
Answer» C. A is correct but R is wrong

Discussion

77.	In a thyristor the gate current is increased, then
A.	anode current will increase
B.	anode current will decrease
C.	anode current will remain constant
D.	anode current may increase or decrease
Answer» D. anode current may increase or decrease

Discussion

78.	A high frequency series inverter consists of
A.	a number of series inverters in series
B.	a number of series inverters in parallel
C.	a number of parallel inverters in parallel
D.	a number of parallel inverters in series
Answer» C. a number of parallel inverters in parallel

Discussion

79.	In a thyristor the gate lead is connected to the n layer near the p layer to which anode is connected.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» C. May be True or False

Discussion

80.	In a 3 phase full converter feeding a highly inductive load, the average load current is 150 A. The peak current through thyristor is
A.	150 A
B.	75 A
C.	50 A
D.	300 A
Answer» B. 75 A

Discussion

81.	The characteristics of which device has peak point and valley point
A.	SCR
B.	PUT
C.	SCS
D.	Shockley diode
Answer» C. SCS

Discussion

82.	A single phase full converter gives maximum and minimum output voltage at firing angles of
A.	0 and 180° respectively
B.	180° and 0° respectively
C.	0 and 90° respectively
D.	90° and 0° respectively
Answer» B. 180° and 0° respectively

Discussion

83.	In auxiliary commutated chopper, the peak value of thyristor current is
A.	equal to peak value of load current
B.	equal to peak value of capacitor current
C.	sum of peak value of load current and capacitor current
D.	none of the above
Answer» D. none of the above

Discussion

84.	The gate lead, in a thyristor is welded to :
A.	p layer to which anode is connected
B.	n layer nearest to the anode terminal
C.	p layer nearest to the cathode terminal
D.	outside n layer
Answer» C. p layer nearest to the cathode terminal

Discussion

85.	A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When α = 0, speed is 600 rpm. If α = 90°, the speed is likely to be
A.	about 300 rpm
B.	about 150 rpm
C.	about 75 rpm
D.	about zero
Answer» B. about 150 rpm

Discussion

86.	Induction heating systems require low frequency inverters.
A.	True
B.	False
C.	May be True or False
D.	Can't say
Answer» C. May be True or False

Discussion

87.	In a single phase semiconverter feeding a highly inductive load, the load current is
A.	sinusoidal
B.	nearly constant
C.	absolutely constant
D.	rectangular
Answer» C. absolutely constant

Discussion

88.	A single phase fully controlled bridge converter is feeding an RLE load. Input voltage is Vm sin ωt and firing angle is α. If average current is I₀, then
A.	A
B.	B
C.	C
D.	D
Answer» B. B

Discussion

89.	A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ωt. The thyristor will conduct
A.	from 0 to 180°
B.	when v > 50 V
C.	from 0 to 90°
D.	When v < 50 V
Answer» C. from 0 to 90°

Discussion

90.	The characteristics of a non-linear resistance is i = kv⁴. If i becomes 100 times, v becomes
A.	about 100 times
B.	about 10 times
C.	about 3 times
D.	about twice
Answer» D. about twice

Discussion

91.	A chopper
A.	converts constant voltage dc into ac and then into variable voltage dc
B.	converts constant voltage dc into variable voltage dc directly
C.	converts ac of one frequency into ac of another frequency
D.	converts ac to dc
Answer» C. converts ac of one frequency into ac of another frequency

Discussion

92.	A single phase full converter can operate in
A.	4 quadrants
B.	3 quadrants
C.	2 quadrants
D.	1 quadrant
Answer» D. 1 quadrant

Discussion

93.	An SUS is
A.	exactly similar to SCR but with higher rating
B.	similar to UJT
C.	PUT and avalanche diode connected in anti parallel
D.	SCR and avalanche diode connected in parallel
Answer» D. SCR and avalanche diode connected in parallel

Discussion

94.	In brushless excitation system of modern alternators, the main exciter is
A.	dc generator
B.	ac generator
C.	either dc or ac generator
D.	induction generator
Answer» C. either dc or ac generator

Discussion

95.	Which of the following devices exhibit negative resistance characteristics?
A.	UJT
B.	PUT
C.	Both UJT and PUT
D.	UJT, PUT and SBS
Answer» D. UJT, PUT and SBS

Discussion

96.	The total number of leads in reverse conducting thyristor is
A.	2
B.	3
C.	1
D.	4
Answer» C. 1

Discussion

97.	A 3 phase series inverter has
A.	12 thyristors
B.	6 thyristors
C.	3 thyristors
D.	3 or 6 thyristors
Answer» C. 3 thyristors

Discussion

98.	Natural commutation can be used in :
A.	DC circuits only
B.	AC circuits only
C.	both AC and DC circuits
D.	none of the above
Answer» C. both AC and DC circuits

Discussion

99.	Two thyristors of the same rating and specifications
A.	will have equal on state voltage drops
B.	will have equal forward blocking voltage for the same current
C.	will have different on state voltage drops
D.	may have equal or different on state voltage drops and equal or different forward blocking voltage's for the same current
Answer» E.

Discussion

100.	Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C.
A.	Both A and R are correct and R is correct explanation of A
B.	Both A and R correct but R is not correct explanation of A
C.	A is correct but R is wrong
D.	A is wrong but R is correct
Answer» D. A is wrong but R is correct

Discussion

Explore topic-wise MCQs in ENGINEERING SERVICES EXAMINATION (ESE).

In a full bridge single phase inverter feeding RLC load

A single phase half wave rectifier circuit has a free wheeling diode. The free wheeling diode will conduct only if

UJT can be used for

The specified maximum junction temperature of thyristors is about

In sinusoidal PWM for inverters the width of different pulses are not the same.

Assertion (A): A high dv/dt may cause triggering of a thyristor.Reason (R): A high dv/dt results in charging current in the thyristor.

A cycloconverter cannot give a frequency higher than input frequency.

The number of leads in an SCR are :

A cycloconverter for single phase operation has

A single phase semiconverter has a freewheeling diode. If the firing angle is α and the load is purely resistive, the periods of conduction and freewheeling respectively are

A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the speed is 1440 rpm. At 25 Hz, the speed is likely to be

A cycloconverter is a group of controlled rectifiers.

In the basic series inverter circuit, the source current has

A 3 phase semiconverter when supplying a certain load has a rectification efficiency of 0.6 and transformer utilisation factor of 0.35. When a 3 phase full converter is supplying the same load

On load tap changer using thyristors can have a maximum of two taps.

In integral cycle control of ac regulators, the period of integral cycle control, i.e., (m + n) T should be

A single phase semiconverter is supplying RLE load and has a freewheeling diode across the load. The firing angle is α. The freewheeling diode conducts for

Which of the following devices has metal-silicon junction?

In thermal ohm's law, temperature and power loss are analogous to

Mc Murray full bridge inverter uses

Which of these commutation methods uses an auxiliary SCR?

A separately excited dc motor is run from a dc source through a chopper. At 600 rpm and rated torque, the duty cycle of chopper is 0.8. At 600 rpm and half the rated torque, the duty cycle is likely to be

A UJT exhibits negative resistance characteristics when

Assertion (A): Inverters and choppers use fast switching thyristors Reason (R): Fast switching SCR has low turn off time.

In single phase half wave regulator, the average current over one full cycle

Assertion (A): The output voltage of an inverter can be controlled by PWM techniqueReason (R): In a current source inverter the input current is constant.

In a thyristor the gate current is increased, then

A high frequency series inverter consists of

In a thyristor the gate lead is connected to the n layer near the p layer to which anode is connected.

In a 3 phase full converter feeding a highly inductive load, the average load current is 150 A. The peak current through thyristor is

The characteristics of which device has peak point and valley point

A single phase full converter gives maximum and minimum output voltage at firing angles of

In auxiliary commutated chopper, the peak value of thyristor current is

The gate lead, in a thyristor is welded to :

A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When α = 0, speed is 600 rpm. If α = 90°, the speed is likely to be

Induction heating systems require low frequency inverters.

In a single phase semiconverter feeding a highly inductive load, the load current is

A single phase fully controlled bridge converter is feeding an RLE load. Input voltage is Vm sin ωt and firing angle is α. If average current is I₀, then

A single phase half wave converter is used to charge a battery of 50 V. The thyristor is continuously fired by dc signal. Input voltage is v = Vm sin ωt. The thyristor will conduct

The characteristics of a non-linear resistance is i = kv⁴. If i becomes 100 times, v becomes

A chopper

A single phase full converter can operate in

An SUS is

In brushless excitation system of modern alternators, the main exciter is

Which of the following devices exhibit negative resistance characteristics?

The total number of leads in reverse conducting thyristor is

A 3 phase series inverter has

Natural commutation can be used in :

Two thyristors of the same rating and specifications

Assertion (A): When an SCR is conducting, the voltage drop across is about 1 V. Reason (R): When an SCR is conducting, the junction temperature is about 200°C.