Most Recently Asked Mechanical Engineering Interview Questions Part – 10

1. Name power losess in rotating electrical machines?

Power losess in rotating electrical machines are Copper losses, core losses, mechanical losses and stray losses.

2. Hysteresis motor is used in…….

Phonographic appliances

3. What is meant by armature reaction?

The effect of armature flu to main flux is called armature reaction. The armature flux may support main flux or opposes main flux.

4. What is the difference between synchronous generator & asynchronous generator?

Synchronous generator supply’s both active and reactive power but asynchronous generator(induction generator) supply’s only active power and observe reactive power for magnetizing.

5. Where should the lighting arrestor be placed in distribution lines?

Near distribution transformers and out going feeders of 11kv and incomming feeder of 33kv and near power transformers in sub-stations.

6. What is encoder?

An encoder is a device used to change a signal (such as a bitstream) or data into a code.

7. Why the capacitors works on ac only?

Generally capacitor gives infinite resistance to dc components(i.e., block the dc components). it allows the ac components to pass through.

8. What is the function of anti-pumping in circuit breaker?

when breaker is close at one time by close push button,the anti pumping contactor prevent re close the breaker by close push button after if it already close

9. What does the KVAR means?

The KVAR indicates the electrical power. KVAR means “Kilo Volt Amperes with Reactive components

10. What is ACSR cable and where we use it?

ACSR means Aluminium conductor steel reinforced, this conductor is used in transmission & distribution.

11. Both have the same principle of electromagnetic induction, the only difference is that their construction. What i’m talking about?

Generator and alternator

12.What is slip in an induction motor?

Slip can be defined as the difference between the flux speed (Ns) and the rotor speed (N). Speed of the rotor of an induction motor is always less than its synchronous speed. It is usually expressed as a percentage of synchronous speed (Ns) and represented by the symbol ‘S’.

13. Why rating of transformer in KVA and for motor rating isi n hp or KW.

Transformer losses depends on current (CU loss) & Voltage (Iron loss) (VA). So its rated in KVA. Also TFR is independent from load PF. But in motor the losses depends of load power factor. That’s why motor rated in KW.

14. For a transmission line, if the magnitude of open circuit input impedance is 100 Ω and magnitude of short circuit input impedance is 25 Ω then the characteristic impedance of transmission line will be ………

50 Ω

15. How is the feed water coming to the economizer in a thermal power plant is heated?

Flue gases

16. Why use the VCB at High Transmission System ? Why can’t use ACB?

Actually the thing is vacuum has high arc queching property compare to air because in VCB ,the die electric strengths equal to 8 times of air . That y always vaccum used as in HT breaker and air used as in LT .

17. In the output of…………..type of power amplifier crossover distortion is exhibited.

Class B

18. Why link is provided in neutral of an ac circuit and fuse in phase of ac circuit?

Link is provided at a Neutral common point in the circuit from which various connection are taken for the individual control circuit and so it is given in a link form to withstand high Amps.

But in the case of Fuse in the Phase of AC circuit it is designed such that the fuse rating is calculated for the particular circuit (i.e load) only.So if any malfunction happen the fuse connected in the particular control circuit alone will blow off.

19. Total 8 memory chips are present in a memory system. Each memory chips has 12 address lines and 4 data lines. The total size of the memory system is………

32 K bytes

20. Why back emf used for a dc motor? highlight its significance.

The induced emf developed when the rotating conductors of the armature between the poles of magnet, in a DC motor, cut the magnetic flux, opposes the current flowing through the conductor, when the armature rotates, is called back emf. Its value depends upon the speed of rotation of the armature conductors. In starting, the value of back emf is zero.

21. What is the difference between MCB & MCCB, Where it can be used?

MCB is miniature circuit breaker which is thermal operated and use for short circuit protection in small current rating circuit. MCCB moulded case circuit breaker and is thermal operated for over load current and magnetic operation for instant trip in short circuit condition.under voltage and under frequency may be inbuilt. Normally it is used where normal current is more than 100A.

22. Let an electric train is driven by a dc series motor that faces a constant power load. It is running at rated speed and rated voltage. In order to bring down the speed to 0.25 p.u. the supply voltage has to be brought down to ……

0.5p.u.

23. Can we improve power factor by connecting static capacitors in parallel with the load operating at lagging power factor?

Yes

24. Explain Demand Factor?

It is defined as the ratio of actual maximum demand made by the load to the rating of the connected load.

25. Explain the term real power in ac circuits?

It is the product of voltage, current and power factor i.e. P = V I cos j and basic unit of real power is watt. i.e. Expressed as W or kW.

26. Transformer losses have two sources……….and magnetic loss

copper loss

27. Name two types of earthing you are familiar?

Equipment earthing and system earthing

28. Tell me about your project?

29. Tell me about your mini project?

30. Where should the lighting arrestor be placed in distribution lines?

Near distribution transformers and out going feeders of 11kv and incomming feeder of 33kv and near power transformers in sub-stations.

31. Is it possible to start up a 36w or 40w 220V AC/DC tube light without the help of Coil or Choke?

It is not possible without the help of electric coil or choke. Because, the coil or choke ionize the particles in the tube light. In normal voltage it is not possible to ionize the particle.

32. Why the capacitor works doesn’t work on DC?

The capacitor normally gives an infinite resistance to DC component. But, it allows AC power component to pass through the devices. These resistances of the capacitor blocks work of DC component.

33. In the …… Stability there is a large duration phenomenon with small disturbance

Static

34. …….Stability refers to artificial stability

Dynamic

35. A big amount of Copper loss is a disadvantages of low power factor – Agree

Yes

36. Define load factor?

The ratio of Average load and the Maximum demand in a given period of time in a power plant is known as load factor.

37. When the pointer of an analog ohmmeter reads close to zero, the resistor being measured is shorted or over heated?

shorted

38. A power supply produces a 0.6 W output with an input of 0.7 W. Its percentage of efficiency is…..

85.7%

39. A half-watt is equal to how many milliwatts?

500 mW

40. The first row of a certain determinant has the numbers 3 and 5. The second row has the numbers 7 and 2. The value of this determinant is – 31 or 39?

value is 39

41. The first row of a certain determinant has the numbers 10 and 6. The second row has the numbers 3 and 5. The value of this determinant is 32 or -32?

32

42. Explain Demand Factor?

The ratio of maximum demand and connected load on the power station is called as demand factor.

43.What will happen if a 220volt AC operated bulb or device run by the 220volt DC?

This high voltage may damage the device.

44. What do you mean by electric traction?

Electric Traction means running a machine by using electric energy or power.

45. Why you choose Electrical Engineering?

tell yourself

46. The rate (dP/dδ) of the differential power increased is obtained per differential load angle increased. This are called as electrical stiffness – True or False?

True

47. The assembly of electrical apparatus whose purpose is changing the some major characteristics of the electric supply system is called ……..

substation

48. Explain Demand Factor?

The ratio of maximum demand and connected load on the power station is called as demand factor.

49. A basic one-loop dc generator is rotated at 90 rev/s. How many times each second does the dc output voltage peak (reach maximum)?

180

50. If the steel disk in a crankshaft position sensor has stopped with the tab in the magnet’s air gap, the induced voltage…….

Zero