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1.
Statement for Linked Answer Questions :
A voltage commutated chopper operating at 1 kHz is used to control the speed of dc motor as shown in figure. The load current is assumed to be constant at 10 A.
[1] The minimum time in µsec for which the SCR M should be On is
[2 marks]
(A) 280
(B) 140
(C) 70
(D) 0[2] The average output voltage of the chopper will be [2 marks]
(A) 70 V
(B) 47.5 V
(C) 35 V
(D) 0 Vlast reply by CpjJwWHV • 12 years ago • asked in Electrical Engineering, 2006
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2.
Statement for Linked Answer Questions :
For a power system the admittance and impedance matrices for the fault studies are as follows.
The pre-fault voltages are 1.0 p.u at all the buses. The system was unloaded prior to the fault. A solid 3 phase fault takes place at bus 2.
[1] The post fault voltages at buses 1 and 3 in per unit respectively are
[2 marks]
(A) 0.24,0.63
(B) 0.31,0.76
(C) 0.33,0.67
(D) 0.67,0.33
[2] The per unit fault feeds from generators connected to buses 1 and 2 respectively are [2 marks]
(A) 1.20, 2.51
(B) 1.55, 2.61
(C) 1.66, 2.50
(D) 5.00, 2.50asked in Electrical Engineering, 2006
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3.
Statement for Linked Answer Questions :
A 300 kVA transformer has 95% efficiency at full load 0.8 pf lagging and 96% efficiency at half load, unity pf.[1] The iron loss (Pi) and copper loss (Pc) in kW, under full load operation are
[2 marks]
(A) Pc = 4.12, Pi = 8.51
(B) Pc = 6.59, Pi = 9.21
(C) Pc = 8.51, Pi = 4.12
(D) Pc = 12.72, Pi = 3.07[2] What is the maximum efficiency (in %) at unity pf load? [2 marks]
(A) 95.1
(B) 96.2
(C) 96.4
(D) 98.1last reply by CpjJwWHV • 12 years ago • asked in Electrical Engineering, 2006
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4.
Statement for Linked Answer Questions :
It is required to design an anti-aliasing filter for an 8 bit ADC. The filter is a first order RC filter with R = 1Ω and C = 1F. The ADC is designed to span a sinusoidal signal with peak to peak amplitude equal to the full scale range of the ADC.
[1] The transfer function of the filter and its roll off respectively are
[2 marks]
(A) 1/ (1 + RCs), -20 dB / decade
(B) (1 + RCs), - 40 dB/decade
(C) 1/(1 + RCs), -40 dB / decade
(D) [RCs / (1 + RCs)], - 20 dB / decade[2] What is the SNR (in dB) of the ADC? Also find the frequency (in decades) at the filter output at which the filter attenuation just exceeds the SNR of the ADC. [2 marks]
(A) 50 dB, 2 decades
(B) 50 dB, 2.5 decades
(C) 60 dB, 2 decades
(D) 60 dB, 2.5 decadesasked in Electrical Engineering, 2006
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5.
Statement for Linked Answer Questions ::
p = [- 10 1 3]T, q = [-2 -5 9]T, r = [2 – 7 12]T are three vectors.[1] An orthogonal set of vectors having a span that contains p,q,r is
[2 marks]
(A) [-6 -3 6]T, [4 -2 3]T
(B) [-4 2 4]T, [5 7 -11]T, [8 2 -3]T
(C) [6 7 -1]T, [-3 12 -2]T, [3 9 -4]T
(D) [4 3 11]T, [1 31 3]T, [5 3 4]T[2] The following vector is linearly dependent upon the solution to the previous problem [2 marks]
(A) [8 9 3]T
(B) [-2 -17 30]T
(C) [4 4 5]T
(D) [13 2 -3]Tasked in Electrical Engineering, 2006
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6.
A generator feeds power to an infinite bus through a double circuit transmission line. A3 phase fault occurs at the middle point of one of the lines. The infinite bus voltage is 1 pu, the transient internal voltage of the generator is 1.1 pu and the equivalent transfer admittance during fault is 0.8 pu. The 100 MVA generator has an inertia constant of 5 MJ/MVA and it was delivering 1.0 pu power prior of the fault with rotor power angle of 30°. The system frequency is 50 Hz.
[1] The initial accelerating power (in pu) will be [2 marks]
(A) 1.0
(B) 0.6
(C) 0.56
(D) 0.4[2] If the initial accelerating power is X pu, the initial acceleration in elect deg/sec2, and the inertia constant in MJ – sec /elect deg respectively will be
[2 marks]
(A) 31.4X,18
(B) 1800X, 0.056
(C) X/1800,0.056
(D) X/31.4,18asked in Electrical Engineering, 2006
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