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ELECTRICAL SUPERVISOR EXAM PAPER 4 MCQS PART 1 P1 Aug 2023

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PAPER 4 - MINE INSTALLATION / खान अधिष्ठापन

Electrical MCQs

1. The location of a diode in the pilot circuit in GEB (Gate End Box) to achieve pilot core protection system is ……………………………….

At the end at pilot circuit At the GEB At the cable reeling drum At the motor

Explanation: A diode is typically placed at the GEB to provide pilot core protection.

2. What is Intrinsically safe circuit used in face machinery of belowground coal mines

It will work with low voltage if it gets short circuited spark cannot ignite the gas around it high voltage circuit None of these

Explanation: Intrinsically safe circuits are designed so that any spark or thermal effect produced under normal or fault conditions is incapable of causing ignition of a hazardous atmosphere.

3. What is the colour code of 5 cores of trailing cable used in mines?

Red, black, blue are used as phase and yellow as pilot and green as earth Red, blue, green are used as phase and black as pilot and yellow as earth Red, yellow, blue are us phase and black pilot and green as earth None

Explanation: The standard color code for a 5-core trailing cable in mines often uses Red, Yellow, Blue for phases, Black for pilot, and Green for earth.

4. In 440V, 3PH system the full load current of 40 HP electric motor is

40A 50A 60A 70A

Explanation: For a 40 HP motor at 440V, 3-phase, the full load current is approximately 50A (calculation: Power in Watts = HP * 746; I = P / (sqrt(3) * V * efficiency * PF)).

5. What are the protective features available in an Air Circuit Breaker (ACB)?

E/L relay protection O/C Protection NO Volt Protection All

Explanation: Air Circuit Breakers (ACBs) typically offer Earth Leakage (E/L), Overcurrent (O/C), and No Volt protection.

6. In a Dash pot type over current relays the time delay setting is adjusted by

Providing thick oil adjusting the striker plate position Providing thin oil not filling with oil

Explanation: In a dashpot type overcurrent relay, the time delay is adjusted by changing the position of the striker plate, which alters the volume of oil to be displaced.

7. In a 3 PH, 550 V AC System the voltage between two phase and the voltage between phase and earth are

317.5V, 550 V 550V, 317.5V 550 V, 230 V 550V, 275 V

Explanation: In a 3-phase, 550V system (line-to-line), the voltage between two phases is 550V. The phase-to-earth voltage (if the system is star-connected with earthed neutral) would be 550V / sqrt(3) ≈ 317.5V.

8. Trailing cable used in below ground mines along with drill machine is

Individually screened 5 core cable collectively screened cable with 5 cores unscreened cable with 4 cores unscreened cable with 5 cores

Explanation: Trailing cables for drill machines in underground mines are typically collectively screened 5-core cables for enhanced safety.

9. High Magnitude currents can be measured by

CT operated multi-meters PTs Ammeters connected with CTs CTs

Explanation: High magnitude currents are safely measured using ammeters connected with Current Transformers (CTs) to step down the current to a measurable level.

10. The Trailing cable used for GEBs in below ground mines must have

5 cores 3 cores 4 cores 6 cores

Explanation: Trailing cables for GEBs in underground mines typically have 5 cores (3 phase, 1 pilot, 1 earth) for power and protection.

11. What is meant by M.C.B.?

Minimum circuit breaker Miniature circuit breaker Monitoring circuit breaker None of these

Explanation: MCB stands for Miniature Circuit Breaker.

12. The Pilot circuit voltage of a GEB used in below ground mines is

Not to exceed 30 Volts More than 30 Volts Not to exceed 15 Volts Not to exceed 8 Volts

Explanation: The pilot circuit voltage in GEBs in underground mines is typically limited to a low voltage, often not exceeding 30V, for safety reasons.

13. What will be the full load current of primary and secondary sides in a 315 KVA, 3.3 KV / 440 V transformer?

45.5A / 400A 55.11A / 413.3A 60.5A / 420.5A None of these

Explanation: Primary Current = (315 * 1000) / (sqrt(3) * 3300) = 55.11A. Secondary Current = (315 * 1000) / (sqrt(3) * 440) = 413.3A.

14. In a star-delta starter, which contractor will be made "ON" during starting of the motor?

Both main and Star contactor Only main contactor Only star contactor None of these

Explanation: During starting, both the main contactor and the star contactor are "ON" to connect the motor in a star configuration.

15. What is the use of pre start alarm used with belt conveyors

Warning white belt conveyor is running warning before starting of belt conveyor Both (a) & (b) None of these

Explanation: A pre-start alarm is used to warn personnel before the belt conveyor starts moving, ensuring safety.

16. In underground mines the minimum insulation resistance of the entire system to be maintained at

1 Kilo ohm 100 kilo ohm 1 Mega ohm 10 Kilo ohm

Explanation: The minimum insulation resistance for electrical systems in underground mines is often specified to be at least 1 Mega ohm for safety.

17. SF6 means

Sulphuric Acid SulpherHexaflouride SupherHexa chloride None of these

Explanation: SF6 stands for Sulfur Hexafluoride, a gas commonly used in high-voltage switchgear due to its excellent dielectric properties.

18. What is the use of HRC Fuse?

They are compact easy to fix when it blown the spark will be extinguished internally None of these

Explanation: High Rupturing Capacity (HRC) fuses are designed to safely extinguish the arc internally when they blow, preventing external sparking.

19. What is the earth leakage current limit specified in below ground mines as per CEAR 2010?

1A 0.5A 750mA 2A

Explanation: As per CEAR 2010, the earth leakage current limit in below-ground mines is often specified as 0.5A or 500mA.

20. What is the level of lighting voltage in below ground mines

110V (PH-PH) with id point earthed 110 (PH-EARTH) 230 V (PH-Earth) None of these

Explanation: For safety in underground mines, the lighting voltage is typically kept low, often 110V phase-to-earth.

21. CBCT is used in Air circuit Breaker (ACB)s for protection against

Earth leakage over current short circuit None of these

Explanation: Core Balance Current Transformers (CBCTs) are primarily used in ACBs for sensitive earth leakage protection.

22. What is purpose of NGR used with the transformers

To limit the fault current level to improve the voltage to improve the power factor None of these

Explanation: Neutral Grounding Resistors (NGRs) are used with transformers to limit the fault current level during earth faults, protecting equipment and personnel.

23. Insulation resistance of a Cable can be measured by

Ammeter Volt meter Ohm meter Megger

Explanation: Insulation resistance is measured using a Megger (Megohmmeter), which applies a high DC voltage and measures the resulting small current to determine resistance.

24. Voltmeter has to be connected in with phases

Series Parallel both of the above None of these

Explanation: Voltmeters are always connected in parallel across the points where voltage is to be measured.

25. How many out going circuits can be connected to one ACB

Max. two circuits only one circuit as many as required None of these

Explanation: Typically, one Air Circuit Breaker (ACB) is designed to protect and control a single outgoing circuit for proper coordination and safety.

26. Rating of transformer shall be in the

Volt, Current Volt, KW Volt, KVA None of these

Explanation: Transformers are rated in KVA (Kilo Volt-Amperes) because their losses depend on voltage and current, not just active power (KW), due to core and copper losses.

27. Electrical shock intensity is based on

Flow of voltage and duration of flow Flow of current and duration of flow Size of the cable None of these

Explanation: The severity of an electrical shock is primarily determined by the magnitude of current flowing through the body and the duration of that flow.

28. While working on Electrical circuits power source should be

Switched off no need to switch off Both (a) & (b) None of these

Explanation: For safety, the power source should always be switched off and locked out before working on electrical circuits.

29. How multi meter can be used while working on electrical circuits?

With using Insulated hand gloves no need to use Insulated gloves Any of the above None of these

Explanation: When using a multimeter on live electrical circuits, it is crucial to use insulated hand gloves for personal protection.

30. How will you release a person who has come in contact with a live electric line.

By pulling him with hands by switching of the mains Any of the above None of these

Explanation: The safest and most immediate action is to switch off the main power supply to de-energize the line. Never pull a person in contact with live wire directly with bare hands.

31. What precaution shall be observed while replacing fuse in live electric circuit

Removing fuse with Insulated had gloves main switch should be switched off Any of the above None of these

Explanation: The main switch should always be switched off to de-energize the circuit before replacing a fuse for safety.

32. What precaution should be observed before putting a main switch to "ON" from "OFF" position?

Use insulated Hand gloves Ensure no one is working on the same line Switch "ON" main directly None of these

Explanation: Before re-energizing a circuit, it's crucial to ensure that no one is working on the line to prevent accidents.

33. Units of resistance

Amps Ohms Volts None of these

Explanation: The SI unit of electrical resistance is the Ohm (Ω).

34. What is the best conductor?

Copper Aluminum Carbon None of these

Explanation: Silver is the best electrical conductor, followed closely by copper. Among the given options, copper is the best conductor.

35. What is the value of total resistance ® in series circuit?

R1+R2+R3… R1xR2xR3…. Any of the above None of these

Explanation: In a series circuit, the total resistance is the sum of individual resistances: R_total = R1 + R2 + R3 + ...

36. Units of power

Volts watts Amps None of these

Explanation: The SI unit of electrical power is the Watt (W).

37. Energy can be stored in

Inductors resistors capacitors None of these

Explanation: Energy can be stored in the electric field of capacitors and in the magnetic field of inductors. Resistors dissipate energy as heat.

38. What is the purpose of breather used in transformers?

Provides dry air to the transformer used to top up the transformer oil To reduce the voltage None of these

Explanation: A breather in a transformer contains silica gel, which absorbs moisture from the air entering the conservator tank, thus providing dry air and preventing insulation degradation.

39. What is the type of cooling system used for transformers?

Water cooling Air Cooling oil cooling All

Explanation: Transformers use various cooling methods, including air cooling (natural or forced), oil cooling (natural or forced), and sometimes water cooling for very large units. Oil cooling is very common for medium and large transformers.

40. Generator is used to …………..

run the engine run the motor Both (a) & (b) None of these

Explanation: A generator is used to convert mechanical energy into electrical energy. It does not run an engine or a motor; rather, an engine might run a generator.

41. In a 3 Phase system what do your mean by phase voltage

Voltage available between two Phases Voltage Available between phase and neutral Voltage available at neutral point None of these

Explanation: In a 3-phase system, phase voltage refers to the voltage between any one phase conductor and the neutral point.

42. In a 3 Phase System what do you mean by line voltage

Voltage available between two phases Voltage Available between phase and neutral Voltage available at neutral point None of these

Explanation: In a 3-phase system, line voltage refers to the voltage available between any two phase conductors.

43. Step up transformer will Voltage.

Steps up Steps down Both (a) & (b) None of these

Explanation: A step-up transformer increases the voltage from its primary side to its secondary side while decreasing the current.

44. Transformers are rated in

KVA KW KVAR None of these

Explanation: Transformers are rated in KVA (Kilo Volt-Amperes) because their losses are primarily dependent on the apparent power, not just the active power (KW), as they have both iron and copper losses.

45. Distribution transformer neutral ……………

should be earthed should not be earthed should be connected with phase None of these

Explanation: The neutral of a distribution transformer should always be earthed for safety and to provide a stable reference point for the low-voltage system.

46. Choice of a cable in electrical circuit is ……………………

dependent on load Independent on load dependent on cost None of these

Explanation: The choice of a cable is primarily dependent on the expected load current it needs to carry safely, to avoid overheating and voltage drops.

47. Electrical installations should be maintained……………..

Dry Wet Humid None of these

Explanation: Electrical installations should always be maintained dry to prevent insulation breakdown, short circuits, and electric shocks.

48. Fuse protection was related with………..

Load current Load Voltage Type of load None of these

Explanation: Fuse protection is primarily related to the load current. Fuses are designed to melt and break the circuit when the current exceeds a safe limit, protecting the circuit from overcurrents.

49. Speed of a AC induction motor can be controlled by

Frequency Voltage Field Resistance All

Explanation: The speed of an AC induction motor is primarily determined by the frequency of the supply voltage and the number of poles. Voltage control also affects speed but less directly. Field resistance control is for DC motors.

50. Earthing of switchgear in below ground mines can be achieved with

Local earth pits in belowground Through cable armour from surface earth pits Both (a) & (b) None of these

Explanation: Earthing in underground mines can be achieved by local earth pits, or more commonly, by extending the earthing system from surface earth pits via the cable armour. Both methods contribute to a robust earthing system.

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