Q .
The two modes of operation of three phase bridge inverters are known as
A. 60° mode and 120° mode
B. 90° mode and 120° mode
C. 120° mode and 180° mode
D. 120° mode and 240° mode
E. NA
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Q .
Two semiconverters are connected in series to form a single phase series converter. The input v = Vm sin ωt and a 1 = a 2 are the firing angles of the two converters. If a 1 = a 2 = 0, the dc output voltage is
A.
B.
C.
D.
E. NA
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Q .
A 3 phase bridge inverter is fed by 400 V battery. The load is star connected and has a resistance of 10 Ω per phase. The peak value of load current is
A. 40 A
B. 20 A
C. 10 A
D. 5 A
E. NA
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Q .
A single phase half wave controlled rectifier circuit is feeding on RL load. The circuit has a freewheeling diode. The input voltage is v = Vm sin ωt. If I0 is the load current during the conduction of freewheeling diode, the KVL equation during the conduction of free wheeling diode is
A.
B.
C.
D.
E. NA
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Q .
A 3 phase ac regulator uses
A. 3 thyristors
B. 6 thyristors
C. 9 thyristors
D. 12 thyristors
E. NA
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Q .
A single phase half wave controlled rectifier circuit has an R-L load. A freewheeling diode is also in the circuit. When freewheeling diode is conducting the SCR
A. is forward biased
B. is reverse biased
C. may be forward biased or reverse biased
D. forward biased initially but reverse biased afterwards
E. NA
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Q .
In a single phase full wave ac regulator the rms value of load current is 20 A load is purely resistive. Then
A. average thyristor current will be less than 20 A but rms thyristor current will be more than 20 A
B. both the average and rms thyristor currents will be less than 20 A
C. both the average and rms thyristor currents will be more than 20 A
D. rms thyristor current will be 20 A and average thyristor current will be 10 A
E. NA
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Q .
A single phase semiconverter is feeding a highly inductive load. The circuit has a freewheeling diode across the load and firing angle is a . During one cycle of input voltage, the total duration of conduction of freewheeling diode is
A. a
B. 2 a
C. 4 a
D. 0.5 a
E. NA
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Q .
A static induction thyristor
A. is a majority carrier device
B. is a minority carrier device
C. either a majority carrier or minority carrier device
D. has a total number of 2 leads
E. NA
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Q .
A thyristor needs protection against
A. high
B. high
C. both high and high
D. either high or high
E. NA
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Q .
Which of these triggering methods for series connected SCRs use LASCR in the gate circuit?
A. Resistance triggering
B. Simultaneous triggering
C. Sequential triggering
D. Optical triggering
E. NA
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Q .
In a 3 phase full wave regulator feeding resistance load connected in star, the possible range of firing angle a is
A. 0 ≤ a ≤ 180°
B. 0 ≤ a ≤ 150°
C. 0 ≤ a ≤ 120°
D. 0 ≤ a ≤ 90°
E. NA
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Q .
Induction heating systems require low frequency inverters.
A. True
B. False
C.
D.
E. NA
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Q .
All inverters use forced commutation.
A. True
B. False
C.
D.
E. NA
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Q . Assertion (A): A dual converter may be circulating current type or non circulating current type.
Reason (R): In circulating current dual converter only one converter can be operated at one 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
E. NA
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Q .
The number of leads in a power semiconductor diode are
A. 2
B. 3
C. 4
D. 2 or 3
E. NA
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Q .
A single phase half wave converter is feeding a resistive load. Just before triggering, the voltage across thyristor is
A. zero
B. about 1 V
C. same as input voltage
D. twice the input voltage
E. NA
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Q .
In a 3 phase full converter the average load current is 150 A. The average thyristor current is
A. 150 A
B. 75A
C. 50 A
D. 25 A
E. NA
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Q .
If ton and toff are the turn on and turn off times of a thyristor, then
A. ton and toff are almost equal
B. ton >> toff
C. toff >> ton
D. ton is about twice toff
E. NA
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Q .
Which of these commutation methods uses an auxiliary SCR?
A. Class A
B. Class B
C. Class C
D. Class D
E. NA
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Q .
In a single phase full wave regulator feeding R-L load, the minimum firing angle can be zero.
A. True
B. False
C.
D.
E. NA
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Q .
In a series inverter supplying a load resistance R, the commutating elements L and C should be such that
A.
B.
C.
D.
E. NA
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Q .
A 750 A circuit uses thyristor of current rating 175 A. If derating is 25%, the number of thyristors in parallel is
A. 3
B. 4
C. 6
D. 10
E. NA
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Q .
In a single phase full wave converter (M - 2 connection), the rms transformer voltage is 300 V across each half of secondary. The PIV for each thyristor is
A. 300 V
B.
C. 6002 V
D.
E. NA
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Q . Assertion (A): An inverter does not require forced commutation
Reason (R): A series inverter is a forced commutation inverter.
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
E. NA
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Q .
A DIAC has two terminals, anode and cathode.
A. True
B. False
C.
D.
E. NA
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Q .
Current chopping leads to
A. over voltage
B. over current
C. both over voltage and over current
D. either over voltage or over current
E. NA
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Q . Assertion (A): The gate current of an SCR is always in the form of pulses.
Reason (R): The gate losses, in pulse triggering, are low.
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
E. NA
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Q .
In an SCR, the anode current is controlled by
A. gate current only
B. external circuit only
C. both gate current and external circuit
D. none of the above
E. NA
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Q .
A dc chopper is feeding an RLE load. The maximum steady state ripple is
A.
B.
C.
D.
E. NA
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Q .
A dc circuit breaker must use
A. natural commutation
B. forced commutation
C. both natural and forced commutation
D. either natural or forced commutation
E. NA
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Q .
A single phase series converter is used for
A. high voltage output
B. high current output
C. high voltage and high current output
D. improving the circuit efficiency
E. NA
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Q .
A dc separately excited motor has a constant field current. The armature is fed from a single phase supply through a semi-converter. When a = 0, speed is 600 rpm. If a = 90°, the speed is likely to be
A. about 300 rpm
B. about 150 rpm
C. about 75 rpm
D. about zero
E. NA
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Q .
In a full wave converter (M - 2 connection) feeding an RLE load, the peak thyristor current is 15 A. For fully controlled bridge circuit and same load current, the peak thyristor current will be
A. 30 A
B. 152 A
C. 15 A
D.
E. NA
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Q .
A thyristor is reverse biased. A positive gate pulse is applied. The thyristor
A. will be turned on
B. may or may not turn on
C. will not turn on
D. will turn on after sometime
E. NA
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Q .
A cycloconverter is
A. ac-dc converter
B. dc-ac converter
C. dc-dc converter
D. ac-ac converter
E. NA
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Q .
A single phase semiconverter has a freewheeling diode. If the firing angle is a and the load is purely resistive, the periods of conduction and freewheeling respectively are
A. p - a and 0
B. p - a and a
C. p + a and 0
D. p + a and a
E. NA
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Q .
HVDC transmission systems generally use
A. 12 pulse converters
B. 6 pulse converters
C. 3 pulse converters
D. either 12 or 6 pulse converters
E. NA
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Q .
The rated current of a thyristor is 40 A. The holding current will be about :
A. 20 A
B. 1 A
C. 100 mA
D. 10 mA
E. NA
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Q .
In integral cycle control the period of on-off control should be more than mechanical time constant of load.
A. True
B. False
C.
D.
E. NA
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Q .
An RC snubber circuit is used to protect a thyristor against :
A. false triggering
B. failure to turn on
C. switching transients
D. failure to commutate
E. NA
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Q .
The number of doped regions in a SCR is
A. 2
B. 3
C. 4
D. 5
E. NA
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Q .
A reactor is used in a dual converter operating in non-circulating current mode.
A. True
B. False
C.
D.
E. NA
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Q .
During forward blocking state of SCR, the voltage and current respectively are
A. high and high
B. low and low
C. high and low
D. low and high
E. NA
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Q .
An SBS can conduct is one direction only.
A. True
B. False
C.
D.
E. NA
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Q .
In a 3 phase full wave regulator feeding a star connected resistance load the input voltage is 400 V line to line. The firing angle is 160°. The line to line output voltage would be
A. 400 V
B. about 100 V
C. about 20 V
D. zero
E. NA
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Q .
A single phase step up cycloconverter changes 50 Hz to 100 Hz. Then one half wave of input will give rise to
A. one half wave of output
B. one full wave of output
C. two full waves of output
D. either (b) or (c)
E. NA
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Q .
In 180° mode of operation of a 3 phase bridge inverter, two thyristors conduct at one time.
A. True
B. False
C.
D.
E. NA
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Q .
The average load current supplied by a thyristor depends on
A. firing angle
B. firing frequency
C. magnitude of gate current
D. all of the above
E. NA
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Q .
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
E. NA