Quiz: Electrical Engineering 26 Oct 2020

Quiz: Electrical Engineering
Exam: SSC JE
Topic: Miscellaneous

Each question carries 1 mark.
Negative marking: 1/4 mark
Time: 10 Minute

Q1. For V-curve for a synchronous motor the graph is drawn between
(a) Armature current and power factor
(b) Field current and armature current
(c) Terminal voltage and power factor
(d) Power factor and field current

Q2. The repulsion-start induction-run motor is used because of:
(a) High starting torque
(b) Good power factor
(c) High efficiency
(d) Minimum cost

Q3. The ratio of puncture voltage to the flashover voltage of an insulator is
(a) Equal to one
(b) Lower than one
(c) Zero
(d) Greater than one

Q4. The resistance welding process requires a
(a) High value of ac current at low voltage
(b) Low value of ac current at high voltage
(c) High value of dc current at low voltage
(d) Low value of dc current at high voltage

Q5. In arc welding, the electrodes are made of
(a) Copper
(b) Aluminum
(c) Graphite
(d) ACSR conductor

Q6. Earth fault relays are
(a) Directional relays
(b) Non-directional relays
(c) Short operate time relays
(d) Long operate time relays

Q7. In which of the single-phase motor the rotor has no teeth or winding?
(a) Universal motor
(b) Split phase Motor
(c) Reluctance Motor
(d) Hysteresis motor

Q8. In a capacitor start single phase induction motor, the current in the
(a) Supply lines leads the voltage
(b) Starting winding lags the voltage
(c) Main winding leads the voltage
(d) Starting winding leads the voltage

Q9. Which of the following welding process uses non-consumable electrode?
(a) LASER welding
(b) MIG welding
(c) TIG welding
(d) Ion-beam welding

Q10. 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

SOLUTIONS
S1. Ans.(b)
Sol. V curve is a plot of the stator current versus field current for different constant loads.

S2. Ans.(a)
Sol. The repulsion-start induction-run motor is used because of high starting torque.
The starting torque of the repulsion start motor is 350 percent with moderate starting current.
It is usually applicable where the starting period is of a long duration because of high inertia of the load. such as the high-speed lift.

S3. Ans.(d)
Sol. Flashover Voltage: The voltage at which the air around insulator breaks down and flashover takes place shorting the insulator is called Flash Over Voltage.
Puncture Voltage: The voltage at which the insulator breaks down and current flows through the inside of insulator is called Puncture Voltage.
As puncture destroys the insulator, it is more serious than flash-over. Therefore, Safety Factor is defined for an Insulator. Safety factor of an Insulator is defined as the ration of Puncture Voltage to the Flash Over Voltage.
Safety Factor = Puncture Voltage / Flash Over Voltage
So, (Puncture Voltage)/(Flash Over Voltage)>1
For pin type insulator the value of Safety Factor is about 10 which mean that Puncture Voltage is 10 times that of Flash Over Voltage.

S4. Ans.(a)
Sol. In welding process step down transformer is used which has low voltage and high current.

S5. Ans.(c)
Sol. In arc welding, the electrodes are made of graphite.

S6. Ans.(b)
Sol. if the fault current passes in either direction in earth fault relay, it gives a trip condition. Hence, earth fault relay is a non-directional relay.

S7. Ans.(d)
Sol. Hysteresis motor doesn’t have teeth or winding; therefore, these motors are free from mechanical vibration.

S8. Ans.(d)
Sol. In the capacitor start inductor motor two winding is used, the main winding and the starting winding. With starting winding, we connect a capacitor so the current flowing in the capacitor leads the applied voltage by some angle 𝟇.

S9. Ans.(c)
Sol. In TIG welding process uses non-consumable TUGSTEN electrode is used.

S10. 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

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