Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.
Q1. A 220 V DC machine has an armature resistance 1 Ω. If the full load current is 20 A, the difference of induced voltage between generator and motor is
(a) 0 V
(b) 20 V
(c) 40 V
(d) 60 V
Q2. Which of the following represents the operating region slips of a 1-phase induction motor?
(a) 0<s<2
(b) -2<s<2
(c) 0<s<1
(d) -1<s<1
Q3. For the protection of transformer against all kinds of incipient faults, which relay is used:
(a) Buchholz relay
(b) Earth-fault relay
(c) Overcurrent relay
(d) All of the above
Q4. What type of earthing is used by transmission lines?
(a) Plate earthing
(b) Rod earthing
(c) Strip earthing
(d) Both (a) & (c)
Q5. What is the dimension of the copper strips used for the strip earthing?
(a) 25 mm * 4 mm
(b) 25 mm * 3 mm
(c) 30 mm * 4 mm
(d) 30 mm * 3 mm
Q6. The illumination at a point 5 metres below a lamp is 6 LUX. The candela power of the lamp is:
(a) 30
(b) 150
(c) 180
(d) 200
SOLUTIONS
S1. Ans.(c)
Sol. in case of generator: E_g=V_t+I_a R_a
In case of motor: E_b=V_t-I_a R_a
∴E_g-E_b=2I_a R_a=2×20×1=40 V
S2. Ans.(a)
Sol. In a 1-phase induction motor, due to both forward and backward torque slips, the operating region lies between 0 and 2. In motoring mode slip is 0 to 1 and breaking mode 1 to 2.
S3. Ans.(a)
Sol. Buchholz relay is used for protection against insulation failure of windings, core heating, fall of oil level, etc.
S4. Ans.(c)
Sol. Strip earthing is used by transmission lines.
S5. Ans.(a)
Sol. Dimension of strip earthing: 25 mm * 4 mm.
S6. Ans.(b)
Sol. Illumination=CP/(distance)^2
∴CP=6×(5)^2=150.
