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HPCL Previous years electronics and Electrical questions with answers
1. Mho relay is usually employed for the protection of
a) Short lines only
b) Medium lines only
c) Long lines only
d) Any line
Ans: Long lines only
2. A modern power semiconductor device IGBT is combines the characteristics of
a) BJT and MOSFET
b) FCT and GTO
c) SCR and MOSFET
d) SCR and BJT
Ans: BJT and MOSFET
3. For a single-phase a.c. to d.c. controlled rectifier to operate in regenerative mode, which of the following conditions should be satisfied?
a) Half –controlled bridge, a 90°, source of e.m.f. in load
c) Full-controlled bridge, a > 90°, source of e.m.f. in load
d) Full-controlled bridge, a 90°, source of e.m.f. in load4. Which is the most suitable power device for high frequency ( more 100 kHz) switching application?
a) Power MOSFET
b) BJT
c) SCR
d) UJT
Ans: Power MOSFET
5. In a thyristor Latching current is ________ than Holding current
a) Equal
b) Less
c) Greater
d) None
Ans: Greater
6. The transfer function of a system is 10/(1+s) when operating as a unity feedback system, the steady state error to a step input will be
a) 0
b) 1/11
c) 10
d) Infinity
Ans: 1/11
7. Which one of the following statements for a dc machine which is provided with inter pole winding (IW) as well as compensating winding (CW) is correct
a) Both IW and CW are connected in series with Armature winding
b) Both IW and CW are connected in parallel with Armature winding
c) IW connected in series but CW is connected in parallel with Armature winding
d) CW connected in series but IW is connected in parallel with Armature winding
Ans: Both IW and CW are connected in series with Armature winding
8. A 0-10 mA PMMC ammeter reads 5mA in a circuit; its bottom control spring snaps out suddenly the meter will now read.
a) 5mA
b) 10mA
c) 2.5mA
d) 0
Ans: 0
9. A dc cumulatively compounded motor delivers rated load torque at rated speed. If series field is short circuited, then the armature current and speed will
a) Both increases
b) Both decreases
c) Increases and decreases
d) Decreases and increases
Ans: Both increases
10. Moving coil in dynamometer wattmeter connected
a) In series with fixed coil
b) Across supply
c) In series with load
d) Across load
Ans: Across supply
11. In an induction machine, if the air gap increased
a) Speed will be reduced
b) Efficiency will be improved
c) Power factor will be lowered
d) Breakdown torque will be reduced
Ans: Power factor will be lowered
12. A CRO screen has ten divisions on the horizontal scale. If a voltage signal 5 sin 314t+45 deg)is examined with a line base settings of 5 msec/div, the number of cycles of signal displayed on the screen will be
a) 0.5 cycles
b) 2.5 cycles
c) 5 cycles
d) 10 cycles
Ans: 2.5 cycles
13. A 3-phase 50HZ SCIM takes a power input of 30 KW at its full load speed of 1440 rpm. Total stator losses are 1 KW. The slip and rotor ohmic losses at full load are
a) 0.02, 600 W
b) 0.04, 580 W
c) 0.04, 1160 W
d) 0.04, 1200 W
Ans: 0.04, 1160 W
14. Thermocouple is used to measure
a) AC
b) DC
c) Both
d) None
Ans: Both
15. The two watt meters measurement the ratio of two meter readings is –(1-sqrt3):( 1+sqrt3) then the power factor is
a) 1
b) 0.866
c) 0.707
d) 0
Ans: 0.707
16. Hays bridge is used to measure___________ and Schering bridge is used to measure____________
a) Inductance, Inductance
b) Inductance, Capacitance
c) Capacitance, Inductance
d) Resistance, Capacitance
Ans: Inductance, Capacitance
17. When sine wave is given as input to Schmitt trigger then its generates
a) Sine wave
b) Saw tooth wave
c) Triangle wave
d) Square wave
Ans: Square wave
18. In Gauss Seidel method the following factors are influenced for operation
a) Acceleration factor
b) Selection of slack buss
c) Both
d) None
Ans: Selection of slack buss*
19.
i. (X’+Y’) A. Low-pass filter function
ii. (X’Y’) B. Sum
iii. (XY) C. NAND
D. Carry
E.NOR
a) i-C, ii-E, iii-D
b) i-C, ii-E, iii-B
c) i-C, ii-B, iii-D
d) i-C, ii-E, iii-A
Ans: i-C, ii-E, iii-D
20. The phase lead compensation is used to
a) Increase rise time and decrease overshoot
b) Decrease both rise time and overshoot
c) Increase both rise time and overshoot
d) Decrease rise time and increase overshoot
Ans: Decrease rise time and increase overshoot
21. Voltage feed back amplifier is a
a) Shunt-Shunt
b) Shunt-Series
c) Series-Shunt
d) Series- Series
Ans: Shunt-Shunt
22. In microprocessor the next instruction to be executed is stored in
a) Program Counter
b) Stack Pointer
c) Memory Pointer
d) Accumulator
Ans: Program Counter
23. The following element retains it energy after source is disconnected
a) Resister
b) Inductor
c) Capacitor
d) Thermistor
Ans:
24. In series RLC circuit at resonant
a) Voltage is in phase with current
b) Current is maximum
c) Inductive reactance = Capacitive reactance
d) All of the above
Ans: All of the above
25.For RC low pass filter R=100 K ohms, C= 5 micro farads then lower cutt of frequency is
a) 1 K HZ
b) 0 HZ
c) 381.3 HZ
d) Infinity
Ans:
26. V=100Sin (1000t+46 deg),I=2Sin (1000t+80 deg) what are the elements in the circuit
a) R=30 ohm, L=30 mH
b) R=30 ohm, C=33.3 micro farads
c) R=40 ohm, L=30 mH
d) R=40 ohm, L=33.3 micro farads
Ans: R=40 ohm, L=33.3 micro farads
27. L=10 mH, I=100Sin50t 0
28. In dielectric measurement, the dielectric loss is proportional to
a) F
b) V
c) I
d) Vsqr
Ans: Vsqr
29. G(s) = (1-s)/s(s+2) then closed loop transfer function is
a) Unstable
b) Stable
c) Marginally stable
d) All
Ans: Stable
30. G(s) = (1+0.5s)/(1+s) find which type of net work it is
a) Lead net work
b) Lag net work
c) Lag – Lead net work
d) Lead – Lag net work
Ans: Lag net work
31. Temperature of electrode in Arc furnace is
a) 1000 deg
b) 1500 deg
c) 1500 deg to 3500 deg
d) 4500 deg
32. In bode plot the point which separates the lower and upper frequencies is called
a) Critical point
b) Cut-off point
33. Nyquest stability is used to determine
a) Absolute Stability
b) Relative Stability
c) Both
d) None
Ans: Both*
34. When 220V dc shunt alternator generating the voltage at rated value. If direction of rotation is reversed, then alternator will
a) Build up its voltage with same polarity
b) Build up its voltage with opposite polarity
c) No build up of voltage
d) None
Ans: No build up of voltage
35. Over lap Angle depends on_________
a) Load inductance
b) Loa capacitance
c) Source inductance
d) Source capacitance
Ans: Source inductance
36. Area under speed time curve gives
a) Time
b) Speed
c) Distance
d) None
Ans: Distance
37. The regulation of Short Transmission lines depends up on
a) Distance of line
b) Frequency
c) Power factor
d) All
Ans: Power factor
38. Which of the following plant is having lowest load factor?
a) Diesel Plant
b) Pumped storage Plant
c) Thermal Plant
d) Nuclear Plant
Ans: Diesel Plan
39. For SR latch whent the out put is undesirable
a) 0, 0
b) 1, 0
c) 0, 1
d) 1, 1
Ans: 1, 1
40. For interrupting capacitive currents which Circuit Breaker (CB) is used
a) SF6 CB
b) Oil CB
c) Vacuum CB
d) Air blast CB
Ans: Vacuum CB
41. For V/F control, when frequency is increased in transformer
a) Core loss component current increases, Magnetizing component current decreases
b) Core loss component current increases, Magnetizing component current increases
c) Core loss component current decreases, Magnetizing component current decreases
d) Core loss component current decreases, Magnetizing component current increases
Ans: Core loss component current decreases, Magnetizing component current decreases
42. In ceiling fan the angle between auxiliary winding a main winding is
a) 0 deg
b) 90 deg
c) 180 deg
d) 360 deg
Ans: 90 deg
43. In a shaded pole motor, shaded rings are used to
a) Field flux production
Ans: Field flux production
44. Practical method of improving string efficiency
a) Increasing crass arms length
b) Using different size of insulators
c) Using different insulator materials
d) Using of guard rings
Ans: Increasing crass arms length*
45. In which type of fault all 3-phase components are equal
a) L-G
b) L-L
c) L-L-G
d) 3-Phase fault
Ans: 3-Phase fault
46. 11/220 KV 100 MVA transformers, the primary base voltage rating is 10 KV then secondary base KV is
a) 10 KV
b) 220 KV
c) 220/sqrt3
Ans: 220/sqrt3*
47. Water hamming effect is occurs in
a) Surge tank
b) Penstock
c) Turbine
d) Reservoir
Ans: Penstock
48. Transient stability can be improved by
a) By putting series capacitor
b) By using dynamic resister
c) Auto re-closers
d) All of the above
Ans: All of the above
49. If sending end voltage is Vs at no-load in a transmission line then receiving end voltage is if ABCD parameters of line is given
a) Vs
b) Vs/A
c) 0
d) Infinity
Ans: Vs/A
50. Harmonics are eliminated by using
a) Skewing of rotor
b) Distribution winding
c) Short pitch winding
d) All of the above
Ans: All of the above
