Power Electronics (3140915) MCQs

MCQs of AC Voltage Controller

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1.
In AC voltage controllers the
(a) variable ac with fixed frequency is obtained
(b) variable ac with variable frequency is obtained
(c) variable dc with fixed frequency is obtained
(d) variable dc with variable frequency is obtained
Answer:

Option (a)

2.
The AC voltage controllers are used in __________ applications.
(a) power generation
(b) electric heating
(c) conveyor belt motion
(d) power transmission
Answer:

Option (b)

3.
In the principle of phase control
(a) the load is on for some cycles and off for some cycles
(b) control is achieved by adjusting the firing angle of the devices
(c) control is achieved by adjusting the number of on off cycles
(d) control cannot be achieved
Answer:

Option (b)

4.
A single-phase half wave voltage controller consists of
(a) one SCR is parallel with one diode
(b) one SCR is anti parallel with one diode
(c) two SCRs in parallel
(d) two SCRs in anti parallel
Answer:

Option (b)

5.
In the integral cycle control method of ac voltage controller
(a) the average power delivered to the load is controlled
(b) the instantaneous power delivered to the load is controlled
(c) the frequency of output voltage is controlled
(d) none of the mentioned
Answer:

Option (a)

6.
In the integral cycle control of ac voltage controller, is the load is on for n cycles and off for m cycles, then the periodicity is given by? Consider the output is sinusoidal.
(a) m/2π(m+n)
(b) n/2π(m+n)
(c) m/π(m+n)
(d) n/π(m+n)
Answer:

Option (b)

7.
If k is the duty cycles of the controller, then the rms value of the output voltage in case of a integral cycle control circuit will be? Consider the input to be sinusoidal with peak value Vm and rms value Vs.
(a) Vs x k
(b) Vs/k
(c) Vs x √k
(d) Vs
Answer:

Option (c)

8.
Single phase half wave AC voltage controller has Vs = 230V and R = 20 Ω. Find the value of the average output voltage at the R load for a firing angle of 45°.
(a) 224 V
(b) -15.17 V
(c) 15.17 V
(d) –224 V
Answer:

Option (b)

9.
A single phase voltage controller has input of 230 V and a load of 15 Ω resistive. For 6 cycles on and 4 cycles off, determine the rms output voltage.
(a) 189 V
(b) 260 V
(c) 156 V
(d) 178 V
Answer:

Option (d)

10.
A single phase voltage controller has input of 230 V and a load of 15 Ω resistive. For 6 cycles on and 4 cycles off, determine the input pf.
(a) 0.6
(b) 0.7746
(c) 0.855
(d) 0.236
Answer:

Option (b)

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