81. A 440 𝑉 dc series motor of negligible resistance and with unsaturated magnetic circuit takes 50 𝐴 when running at a certain speed on a given load. If the load torque varies as the cube of the speed, the resistance necessary to reduce the speed by 50 % will be:
(a) 20.5 Ω
(b) 24.0 Ω
(c) 28.5 Ω
(d) 32.0 Ω
(b) 24.0 Ω
(c) 28.5 Ω
(d) 32.0 Ω
Answer: (a)
82. A 220 𝑉 shunt motor has an armature resistance of 0.5 Ω and takes armature current of 40 𝐴 at full load. To raise the speed by 50 % if developed torque is constant, the main flux to be reduced will be:
(a) 49.0 %
(b) 45.0 %
(c) 41.5 %
(d) 37.5 %
(a) 49.0 %
(b) 45.0 %
(c) 41.5 %
(d) 37.5 %
Answer: (d)
83. A 3-phase, 6-pole induction motor is connected to a 60 Hz supply. The voltage induced in the rotor bars is 4 𝑉 when the rotor is at standstill. The voltage and frequency induced in the rotor bars at 300 rpm will be:
(a) 3 𝑉 and 45 Hz
(b) 3 𝑉 and 55 Hz
(c) 4 𝑉 and 45 Hz
(d) 4 𝑉 and 55 Hz
(a) 3 𝑉 and 45 Hz
(b) 3 𝑉 and 55 Hz
(c) 4 𝑉 and 45 Hz
(d) 4 𝑉 and 55 Hz
Answer: (a)
84.
Which of the above statements are correct?
(a) 1, 2 and 3
(b) 1 and 2 only
(c) 1 and 3 only
(d) 2 and 3 only
(a) 1, 2 and 3
(b) 1 and 2 only
(c) 1 and 3 only
(d) 2 and 3 only
Answer: (b)
85. A 3300 𝑉 , delta-connected motor has a synchronous reactance per phase (delta) of 18 Ω. It operates at a leading power factor of 0.707 when drawing 800 kW from the mains. The excitation emf will be:
(a) 2871 𝑉
(b) 2653 𝑉
(c) 2435 𝑉
(d) 2217 𝑉
(a) 2871 𝑉
(b) 2653 𝑉
(c) 2435 𝑉
(d) 2217 𝑉
Answer: (a)
86. Which of the following are the essential elements of an automatic control system?
1. Controller which normally incorporates power amplification
2. A comparison device or error detector
3. A measuring device
1. Controller which normally incorporates power amplification
2. A comparison device or error detector
3. A measuring device
(a) 1 and 2 only
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
(b) 1 and 3 only
(c) 2 and 3 only
(d) 1, 2 and 3
Answer: (d)
87. In transmission lines, non uniformity of current distribution is caused by:
(a) Hall effect
(b) Proximity effect
(c) Faraday effect
(d) Inductive effect
(a) Hall effect
(b) Proximity effect
(c) Faraday effect
(d) Inductive effect
Answer: (b)
88. The ratio error regarding accuracy of a current transformer depends on:
1. Nominal ratio
2. Secondary current
3. Primary current
1. Nominal ratio
2. Secondary current
3. Primary current
(a) 1, 2 and 3
(b) 1 and 2 only
(c) 1 and 3 only
(d) 2 and 3 only
(b) 1 and 2 only
(c) 1 and 3 only
(d) 2 and 3 only
Answer: (a)
89. In power system relays the load shed depends on:
1. Self regulating factor 𝑑𝑑
2. Power deficit in percent 𝐷𝐷
3. System normal frequency 𝑓𝑓𝑠
4. Frequency at any time 𝑓𝑓
1. Self regulating factor 𝑑𝑑
2. Power deficit in percent 𝐷𝐷
3. System normal frequency 𝑓𝑓𝑠
4. Frequency at any time 𝑓𝑓
(a) 1, 2 and 3 only
(b) 1, 2 and 4 only
(c) 3 and 4 only
(d) 1, 2, 3 and 4
(b) 1, 2 and 4 only
(c) 3 and 4 only
(d) 1, 2, 3 and 4
Answer: (d)
90. Which one of the following is not a main block of solid-state relays?
(a) Circuit breakers
(b) Comparators
(c) Time delay units
(d) Level detectors
(a) Circuit breakers
(b) Comparators
(c) Time delay units
(d) Level detectors
Answer: (a)
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