০০। A 3 kV circuit uses SCR of 800 V rating. If derating is 25%, the number of SCRs in series is
ক) 4
খ) 5
গ) 6
ঘ) 8
০১। A 3 phase ac regulator uses
ক) 3 thyristors
খ) 6 thyristors
গ) 9 thyristors
ঘ) 12 thyristors
০২। 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
ক) 40 A
খ) 20 A
গ) 10 A
ঘ) 5 A
০৩। 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 thyristor current is
ক)
খ)
গ)
ঘ)
০৪। A 3 phase dual converter consists of
ক) two 3 phase semiconverters connected in parallel
খ) two 3 phase semiconverters connected in antiparallel
গ) two 3 phase full converters connected in antiparallel
ঘ) two 3 phase full converters connected in parallel
০৫। A 3 phase fully controlled bridge converter is fed by a 3 phase system having phase voltage v = Vm sin ωt. The firing angle is a. The dc output voltage is
ক)
খ)
গ)
ঘ)
০৬। A 3 phase fully controlled converter is a
ক) 3 pulse converter
খ) 6 pulse converter
গ) 2 pulse converter
ঘ) 12 pulse converter
০৭। 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
ক) about 1350 rpm
খ) about 720 rpm
গ) about 360 rpm
ঘ) either (b) or (c)
০৮। A 3 phase induction motor is controlled by voltage and frequency control such that the ratio V/f is constant. At 50 Hz, the starting torque is 100 N-m. At 25 Hz, the starting torque
ক) will be less than 100 N-m
খ) will be more than 100 N-m
গ) may be more or less than 100 N-m depending on motor parameters
ঘ) very small
০৯। A 3 phase induction motor is fed by a 3 phase ac regulator to change the stator voltage. The variation in speed will be more if
ক) load torque is constant
খ) load torque increases with increase in speed
গ) load torque decreases with increase in speed
ঘ) either (a) or (b)
১০। 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
ক) rectification efficiency will be more than 0.6 and TUF will be more than 0.35
খ) rectification efficiency will be more than 0.6 but TUF will be less than 0.35
গ) rectification efficiency will be less than 0.6 and TUF will be less than 0.35
ঘ) rectification efficiency will be less than 0.6 but TUF will be more than 0.35
১১। A 3 phase series inverter has
ক) 12 thyristors
খ) 6 thyristors
গ) 3 thyristors
ঘ) 3 or 6 thyristors
১২। A 750 A circuit uses thyristor of current rating 175 A. If derating is 25%, the number of thyristors in parallel is
ক) 3
খ) 4
গ) 6
ঘ) 10
১৩। A bridge type single phase cycloconverter changes the frequency f to f/3. Then one half wave of output contains
ক) 3 full waves of input
খ) 3 half waves of input
গ) 6 full waves of input
ঘ) 6 half waves of input
১৪। A capacitor C farads is charged to a voltage V. It discharges through a thyristor, a diode and an inductance L. The peak current in the circuit is
ক) VCL
খ)
গ)
ঘ)
১৫। A chopper
ক) converts constant voltage dc into ac and then into variable voltage dc
খ) converts constant voltage dc into variable voltage dc directly
গ) converts ac of one frequency into ac of another frequency
ঘ) converts ac to dc
১৬। A chopper cannot be line commutated.
ক) True
খ) False
১৭। A chopper is a high efficiency circuit.
ক) True
খ) False
১৮। A class A chopper has an input voltage of 200 V. Ton = 1.5 ms and Toff = 4.5 ms. The duty cycle, average output voltage and ripple factor respectively are