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Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE) PDF Download

Q21: A phase-controlled, single-phase, full-bridge converter is supplying a highly inductive DC load. The converter is fed from a 230 V, 50 Hz, AC source. The fundamental frequency in Hz of the voltage ripple on the DC side is     (SET-2(2017))
(a) 25
(b) 50
(c) 100
(d) 300
Ans:
(c)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)All even harmonics are present.
Fundamental frequency = 2fs = 2 x 50 =100Hz

Q22: In the circuit shown, the diodes are ideal, the inductance is small, and Io ≠ 0. Which one of the following statements is true?     (SET-2 (2017))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 𝐷1D1 conducts for greater than 180° and D2 conducts for greater than 180°
(b) 𝐷2D2 conducts for more than 180° and D1 conducts for 180°
(c) D1 conducts for 180° and D2 conducts for 180°
(d) D1 conducts for more than 180° and D2 conducts for 180°
Ans:
(a)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Both diodes will conduct for more than 180°.

Q23: The figure below shows an uncontrolled diode bridge rectifier supplied form a 220 V, 50 Hz 1-phase ac source. The load draws a constant current I= 14A. The conduction angle of the diode D1 in degrees is___________.         (SET-1 (2017))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 180.25
(b) 44.64
(c) 224.17
(d) 28.48
Ans: 
(c)
Sol: Average reduction in output voltage due to source inductance = ΔVd0
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q24: A single-phase bi-directional voltage source converter (VSC) is shown in the figure below. All devices are ideal. It is used to charge a battery at 400 V with power of 5 kW from a source V= 220 V (rms), 50 Hz sinusoidal AC mains at unity p.f. If its AC side interfacing inductor is 5 mH and the switches are operated at 20 kHz, then the phase shift (δ) between AC mains voltage (Vs) and fundamental AC rms VSC voltage (Vc1), in degree, is _________.      (SET-2 (2016))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 2.6
(b) 6.8
(c) 6.8
(d) 8.7
Ans: 
(c)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q25: A full-bridge converter supplying an RLE load is shown in figure. The firing angle of the bridge converter is 120°. The supply voltage vm(t) = 200πsin(100πt)V, R = 20Ω, E = 800 V. The inductor L is large enough to make the output current IL a smooth dc current. Switches are lossless. The real power fed back to the source, in kW, is __________.      (SET-2 (2016))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 4
(b) 5
(c) 6
(d) 7
Ans: 
(c)
Sol:Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q26: A three-phase diode bridge rectifier is feeding a constant DC current of 100 A to a highly inductive load. If three-phase, 415 V, 50 Hz AC source is supplying to this bridge rectifier then the rms value of the current in each diode, in ampere, is _____________.       (SET-2 (2016))
(a) 24.6
(b) 36.4
(c) 57.7
(d) 92.4
Ans:
(c)
Sol: In the 3 − ϕ diode bridge rectifier each diode conducts for 120° for one complete cycle.
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q27: A single-phase thyristor-bridge rectifier is fed from a 230 V, 50 Hz, single-phase AC mains. If it is delivering a constant DC current of 10 A, at firing angle of 30°, then value of the power factor at AC mains is       (SET-1 (2016))
(a) 0.87
(b) 0.9
(c) 0.78
(d) 0.45
Ans:
(c)
Sol: Input power factor = power factor at ac mains = C.D.F. × D.F.
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q28: In the given rectifier, the delay angle of the thyristor T1 measured from the positive going zero crossing of Vs is 30°. If the input voltage Vs is 100sin(100πt) V, the average voltage across R (in Volt) under steady-state is _______.          (SET-2 (2015))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 32.32
(b) 45.82
(c) 61.53
(d) 82.45
Ans:
(c)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q29: In the following circuit, the input voltage Vin is 100sin(100 πt). For 100 π RC = 50, the average voltage across R (in Volts) under steady-state is nearest to         (SET-2 (2015))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 100
(b) 31.8
(c) 200
(d) 63.6
Ans:
(c)
Sol: Given, 
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)For one cycle ωτ = 2π rad = 6.28
[ωτ = 25]>>[ωτ = 2π rad = 6.28]
Each capacitor voltage is approximately equal to
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q30: A diode circuit feeds an ideal inductor as shown in the figure. Given vs = 100sin(ωt)V, where ω = 100π rad/s, and L = 31.83mH. The initial value of inductor current is zero. Switch S is closed at t = 2.5ms. The peak value of inductor current iL(in A) in the first cycle is _____.         (SET-3 (2014))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 8.45
(b) 17.07
(c) 22.62
(d) 28.28
Ans:
(b)
Sol: At t = 2.5 ms the circuit is as shown below
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Integrating on both sides
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)when t = 0.0025 sec, at this instant i(t) = 0
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)The peak value of the inductor current will be at (ωt = πc)
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q31: A three-phase fully controlled bridge converter is fed through star-delta transformer as shown in the figure.
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)The converter is operated at a firing angle of 30°. Assuming the load current (I0) to be virtually constant at 1 p.u. and transformer to be an ideal one, the input phase current waveform is          (SET-3 (2014))
(a) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(b) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(c) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(d) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Ans:
(b)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Let us assume all the impedance are Z and to flow I0 only closed path is required. So, in three phases one phase is open circuited.
According to correct division,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)The transformer ratio is given as 1 : K
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)According to 3 phase source waveform,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q32: A fully controlled converter bridge feeds a highly inductive load with ripple free load current. The input supply (Vs) to the bridge is a sinusoidal source. Triggering angle of the bridge converter is α = 30°. The input power factor of the bridge is      (SET-2  (2014)
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 0.25
(b) 0.50
(c) 0.78
(d) 0.98
Ans: 
(c)
Sol: The input power factor (PF) is defined as
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q33: The figure shows the circuit diagram of a rectifier. The load consists of a resistance 10 Ω and an inductance 0.05 H connected in series. Assuming ideal thyristor and ideal diode, the thyristor firing angle (in degree) needed to obtain an average load voltage of 70 V is ____.     (SET-1 (2014))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 7
(b) 70
(c) 140
(d) 1400
Ans: 
(b)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q34: The figure shows the circuit of a rectifier fed from a 230 V (rms), 50-Hz sinusoidal voltage source. If we want to replace the current source with a resistor so that the rms value of the current supplied by the voltage source remains unchanged, the value of the resistance (in ohms) is _____. (Assume diodes to be ideal.)       (SET-1 (2014))
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 23
(b) 46
(c) 13
(d) 79
Ans:
(a)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q35: Thyristor T in the figure below is initially off and is triggered with a single pulse of width 10 μs. It is given that L = (100/π)μH and  C = (100/π)μF Assuming latching and holding currents of the thyristor are both zero and the initial charge on C is zero, T conducts for        (2013)
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 10 μs
(b) 50 μs
(c) 100 μs
(d) 200 μs
Ans:
(c)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Conduction time,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q36: A half-controlled single-phase bridge rectifier is supplying an R-L load. It is operated at a firing angle α and the load current is continuous. The fraction of cycle that the freewheeling diode conducts is       (2012)
(a) 1/2
(b) (1α/π)(1−α/π)
(c) α/2π
(d) α/π
Ans:
(d)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Freewheeling diode conducts for 2α over complete cycle
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q37: The fully controlled thyristor converter in the figure is fed from a single-phase source. When the firing angle is 0°, the dc output voltage of the converter is 300 V. What will be the output voltage for a firing angle of 60°, assuming continuous conduction       (2010)
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(a) 150 V
(b) 210 V
(c) 300 V
(d) 100 V
Ans
(a)
Sol: For firing angle, α, average output voltage of the converter is given by
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q38: A three phase fully controlled bridge converter is feeding a load drawing a constant and ripple free load current of 10 A at a firing angle of 30°. The approximate Total harmonic Distortion (%THD) and the rms value of fundamental component of input current will respectively be       (2008)
(a) 31% and 6.8A
(b) 31% and 7.8A
(c) 66% and 6.8A
(d) 66% and 7.8A
Ans:
(b)
Sol: Load current = I0 = 10A
RMS value of total source current
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Supply current is can be expressed by fourier series,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)RMS value of fundamental current,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Q39: A single-phase half controlled converter shown in the figure feeding power to highly inductive load. The converter is operating at a firing angle of 60°.
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)If the firing pulses are suddenly removed, the steady state voltage (v0) waveform of the converter will become        (2008)
(a) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(b) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(c) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)(d) Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Ans:
(a)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Single phase half controlled converter.
As load is highly inductive, it means laod current is continuous and almost constant.
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)During,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Now, if firing pulses are removed after T1 is triggered at 2π + α.
At ωt = 3π + α, no firing pulse will be available to trigger T2. So, load current will flow through T1D2 as load current is continuos. So during  3π + α < ωt < 4π,  T1D2 will continue to conduct and V0 = 0.
At ωt = 4π, D1 will become forward biassed and D2 will become reverse biased. So, Dwill conduct and T1 is already conducting.
So, load current will flow through T1D1 and V0 = Vs.

Q40: A single phase fully controlled bridge converter supplies a load drawing constant and ripple free load current, if the triggering angle is 30°, the input power factor will be        (2008)
(a) 0.65
(b) 0.78
(c) 0.85
(d) 0.866
Ans: 
(b)
Sol: Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Average output voltage
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)Average output current = I0 (constant)
RMS value of supply current  = I= I0
RMS value of supply voltage = Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)
Input power factor,
Previous Year Questions- Phase Controlled Rectifiers - 2 | Power Electronics - Electrical Engineering (EE)

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FAQs on Previous Year Questions- Phase Controlled Rectifiers - 2 - Power Electronics - Electrical Engineering (EE)

1. What is a phase-controlled rectifier?
Ans. A phase-controlled rectifier is a type of rectifier circuit that converts alternating current (AC) to direct current (DC) by controlling the firing angle of thyristors or other semiconductor devices.
2. How does a phase-controlled rectifier work?
Ans. In a phase-controlled rectifier, the firing angle determines when the thyristors conduct current from the AC supply to the load. By varying the firing angle, the rectifier can control the amount of DC output voltage.
3. What are the applications of phase-controlled rectifiers?
Ans. Phase-controlled rectifiers are commonly used in motor speed control, voltage regulation, power supplies, battery charging, and DC motor drives.
4. What are the advantages of phase-controlled rectifiers?
Ans. Some advantages of phase-controlled rectifiers include improved power factor, reduced harmonics, high efficiency, and the ability to control the output voltage.
5. How does a phase-controlled rectifier differ from a diode rectifier?
Ans. A phase-controlled rectifier can control the output DC voltage by adjusting the firing angle, while a diode rectifier produces a fixed DC output voltage. Additionally, phase-controlled rectifiers have better efficiency and power factor compared to diode rectifiers.
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