paper Electrical engineering BHEL
Sample Solved Questions objective type
BHEL supervisor trainee model question paper
1. Consider the following situations / conditions for a phase-controlled convener:
1. Firing angle is varied hi the range of 900 to 180°.
2. Firing angle is varied in the range of zero to 90°.
3. feeds a load compring RL and additional back emf lead.
4. Feeds a load comprising RL and additional dc voltage source.
A phase-controlled converter will operate as an inverter only when
(a) 1 and 3 are simultaneously satisfied
(b) 2 and 4 simultaneously satisfied
(c) 2 and 3 are simultaneously satisfied
(d) 1 and 4 are simultaneously satisfied.
Ans:-D
2. A dc chopper has a resistive load of 10 ohms and an input voltage of 220 V. When the chopper switch is ‘ON’, its voltage drop is 2V and the chopping frequency is I kHz. If the duty cycle is 50%, then the average output voltage will be
(a) 100V
(b) l03V
(c) 106V
(d) 109V
Ans:-D
3. A voltage control bus is characterised by the specified values of
(a) real and reactive powes
(b) real power and voltage phase angle
(c) real power and voltage magnitude
(d) reactive power and voltage magnitude
Ans:-C
4. A system is said to be effectively grounded only if R0 / X1 and X0 / X1 are respectively (symbols have the usual meanings)
(a) greater than or equal to 1 and less than or equal to 3
(b) less than or equal to 1 and greater than or equal to 3
(c) greater than or equal to 2 and less than or equal to 2
(d) less than or equal to 2 and greater than or equal to 2
Ans:-A
5. Match List I (Coils of a harmonic restrained percentage bias differential relay used for power transformer protection) with List II (Currents flowing through the relay coil) and select the correct answer using the codes given below the lists:
List I
A. Operating coil
B. Restraining coil
C. Bias coil
List II
1. Through current
2. Differential current
3. Second harmonic current
Codes:
A B C
(a) 1 3 2
(b) 2 3 1
(c) 3 2 1
(d) 2 1 3
Ans:-B
6. A composite transmission and distribution network has lines working at different voltages Match List I (Voltage level used) with List II (Type of relays used for protection) and select the correct answer using the codes given below the lists
List I
A. 220kV
B. 33kV
C. 11kV
List II
1. Directional time lag over current relays
2. Carrier current relays
3. Distance relays
Codes:
A B C
(a) 1 3 2
(b) 3 2 1
(c) 2 1 3
(d) 2 3 1
Ans:-B
7. Consider the following statements:
A differential relay is used for a 3-phase transformer protection to avoid maloperation
due to
1. saturation of current transformer.
2. mismatching of the current ratio for current transformers.
3. difference in connections on both sides of power transformer.
4. current setting multipliers.
Of these statements:
(a) 1 and 4 are correct
(b) 1 and 2 are correct
(c) 1, 2 and 3 are correct
(d) 2, 3 and 4 are correct
Ans:-C
8. A dc reactor is connected in series with each pole of a converter station in order to
(a) prevent commutation failures in the inverter
(b) supply reactive power to the converter
(c) improve system stability
(d) increase the power transfer capability
Ans:-C
9. The power transmission capability of bipolar lines is approximately
(a) half that of 3-phase single circuit line
(b) the same as that of 3-phase single circuit line
(c) twice that of 3-phase single circuit line
(d) thrice that of 3-phase single circuit line
Ans:-B
Directions: The following ten items consist of two statements, one labelled, the ‘Assertion A’ and the other labelled the ‘Reason R’. You are to examine these two statements carefully and decide if the Assertion A and the Reason Rare individually true
and if so, whether the Reason is a correct explanation of the Assertion. Select your answers to these items using the codes given below and mark your answer sheet accordingly.
Codes:
(a) Both A and R is true and R Is the correct explanation of A
(b) Both A and R is true but R is not a correct explanation A
(c) A is true but R is false
(d) A Is false but R Is true
10. Assertion (A): The steady-state error due to step input to a system represented by G(s) = 10 (1+ 0.5s) / s(1+s)(1+2s) is zero.
Reason (R) : For a type 1 system, the steady- state error due to step input is zero.
Ans:-A
11. Assertion (A) : In an error detector using a synchro transmitter and a synchrocontrol transformer, the later is connected to the servo amplifier.
Reason (R) : The synchro transmitter is a salient pole device and the control transformer had a low reluctance rotor.
Ans:-A
12. Assertion (A) : Vertical deflection sensitivity of a CRO is higher than that of the horizontal system.
Reason (R) : Sweep voltage is applied to the horizontal deflecting plates.
Ans:-A
13. Assertion (A) : In a class B push-pull power amplifier, there is no power loss under no signal condition.
Reason (R) : The two transistors are biased at cut-off.
Ans:-A
14. Assertion (A): Some compromise is necessary while selecting the value of commutating capacitors of a bistable multivibrator.
Reason (R) : Smaller commutating capacitors yield shorter transition time and longer setting time.
Ans:-B
15. Assertion (A) : For TV transmission, microwave links are preferred over coaxial cables.
Reason (R) Microwave links have greater bandwidth.
Ans:-B
16. Assertion (A) : The no-load current of star/star connected bank of three single-phase transformers contains all harmonics except the triplen harmonics.
Reason (R): Saturation of the core is responsible for the harmonics in the no-load current of a single-phase transformer.
Ans:-B
17. Assertion (A): The inductive voltage drop caused at the terminals of an ac to dc converter at given value of local current does not depend upon the
firing angle.
Reason (R) : The overlap of conduction of incoming and outgoing thyristors is responsible for the inductive voltage drop.
Ans:-C
18. Assertion (A) : Time lag is invariably provided in the majority of protective relaying schemes for the protection of various elements of the electrical power system network.
Reason (R) : Time lag is provided to permit discrimination between main and back-up protection.
Ans:-B
19. Assertion (A) : Insulators should have high impulse ratio and lighning arrestors should have low impulse ratio.
Reason (R): Lightning arrestors are required to divert surge currents to the ground.
Ans:-A
20. For an ac circuit, if e(t) = 160 sin (wt + 10° and i(t) = 5sin (wt — 200), then the reactive power absorbed by the circuit will be
(a) 400 Vars
(b) 346.4 Vars
(c) 200 Vars
(d) 136.8 Vars
Ans:-B
21. For a two-port network, match List I with List II and select the correct answer using the codes given below the lists:
List I
(Impedance Function)
A. z11
B.z22
C. z12
D.z21
List II
(Equivalent transmission coefficient)
1. D/C
2. A/C
3. I/C
4. Delta T/C
Codes:
A B C D
(a) 2 1 4 3
(b) 1 2 3 4
(c) 2 1 3 4
(d) 1 2 4 3
Ans:-A
22. The effect of phase-lead compensator on gain cross-over frequency Wcg and the bandwidth W b is that
(a) Both increase
(b) Both decrease
(c) W cg increase while W b decreases
(d) W cg decreases while W b increases
Ans:-A
23. If R and X are the resistance and inductive reactance respectively, D and L are the diameter and length respectively of the rotor of a two- phase ac servomotor, then the ratios D/L and X / R will be respectively
(a) Large and large
(b) Large and small
(c) Small and large
(d) Small and small
Ans:-D
24. In the case of an armature controlled dc motor, f the equivalent moment of inertia of the motor and load is made small and the armature resistance is reduced, then the motor tends to act like
(a) A differentiating circuit
(b) An integrating circuit
(c) A PID controller
(d) A second order critically damped system
Ans:-D
25. A dc shunt generator is running at rated speed developing its rated voltage. Match List-I (condition of operation) with List-II (effect) and select the correct answer using the codes given below the lists:
List-I
A. The direction of rotation, residual magnetism and field connections are reversed.
B. The direction of residual magnetism and field connections are reversed.
C. The direction of rotation and connection of the field winding are reversed.
D. The direction of rotation and residual magnetism are reversed
List-II
1. The generator will build up with same polarity.
2. The generator will build up with reversed polarity.
3. The generator will not build up.
Codes:
A B C D
(a) 1 3 2 2
(b) 3 2 1 2
(c) 3 2 2 1
(d) 2 3 1 1
Ans:-B
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