Power Plant Instrumentation engineer Interview Question

Interview Q & A Instrumentation
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Interview Questions and Answers : Power Plant Instrumentation and Electrical Engineers

  1. Name the four major circuits in steam power plant. • Coal and ash circuit • Air and flue gas circuit • Feed water and steam circuit • Cooling water circuit
  2. What consists of cooling water circuit and coal & ash circuit in steam power plant? The cooling water circuit consists of a pump, condenser and cooling tower. The coal and ash circuit consists of coal delivery, preparation of coal, handling of coal to the boiler furnace, ash handling and ash storage.
  3. What is the main purpose of the reservoir? The main purpose of reservoir is to store water received from catchments areas during the rainy seasons and supply the same during the dry season.
  4. What is the main purpose of the dam? The main purpose of the dam is to increase the height of water level and also to increase the working head of the hydraulic power plant.
  5. What is the use of surge tank? The surge tank is used to provide better regulation of water pressure in the system. The surge tank controls the water when the load on the turbine decreases and supplies water when the load on the turbine increases. Thus, surge tank controls the pressure variations resulting from the rapid changes in water flow in penstock and hence prevents water hammer.
  6. Explain about penstock? The pipe between surge tank and prime mover is known as penstock. It is designed t o withstand high pressure. It is made up of reinforced concrete. In very cold areas, the penstock is buried to prevent ice formation and to reduce the expansion joints.
  7. What is the use of spill Ways? Spillway is like a safety valve of the dam. It discharges major flood without damaging the dam. It keeps the reservoir level below the maximum level allowed.
  8. What is the main purpose of high-pressure boilers? The high-pressure boilers are used to increase the efficiency of the plant and to reduce the cost of electricity production.
  9. State important advantages of high-pressure boilers? • The amount of scale formation is less, since the velocity of water through pipes are more. • All parts of the system are heated uniformly, so there is no danger of overheating.
  10. Name important high pressure boilers? • La Mont boiler • Benson boiler • Loeffler boiler • Velox boiler.
  11. Name the different types of coal transforming equipments? A. Belt conveyors B. Screw conveyors C. Bucket elevators D. Grab bucket elevators E. Skip hoists F. Flight conveyors. The coal transfer starts by carrying of coal from-unloading point to the storage site.
  12. Define forced draft and induced draft cooling towers If the fan is located at the bottom of the tower and air is blown by the fan up through the descending water it is called as forced draft cooling towers If the fan is located at the top of the tower and air enters through the louvers located on the tower’s side and drawn up and discharge through the fan casing, it is called as induced draft

13 Name the different components of nuclear reactor?

  1. Nuclear fuel
  2. Moderator
  3. Control rods
  4. Reflectors
  5. Reactor vessel
  6. Biological shielding
  7. Coolant

14 Define speed. Speed is a variable which refers to the revolutions per minute of some piece of rotating equipment.

15 Which is the most frequently used speed measuring instrument? Tachometer

16 What are the types of tachometer?

a) A.C. tacho generator b) D.C. tacho generator

17.What are the types of D.C.tacho generator?

a) Permanent magnet type b) Separately excited field type

18.What are the disadvantages of D.C. tacho generator? A.C. ripple is present in the output signal. The magnitude of the ripple is 2% of the out[ut D.C.level.

19.Name the types of rotor used in A.C.tacho generators. a) Drag cup rotor b) Squirrel cage rotor

20.What are the advantages of Squirrel cage rotor? *Cheaper *Occupies less space

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21 Give the formula to calculate the shaft speed.

Shaft spped = (disk speed * No. of openings in the disk) / No.of images

22 Define torque. Torque is defined as the force which tends to change the linear motion or rotation of a body.

23 What is the other name for inline stationary torque sensor? Relative regular twist torque sensor

24 What are the types of torque transducer? i) Inline rotating torque sensor ii) Inline stationary torque sensor iii) Optical torque sensor iv) Proximity torque sensor

25 What are the advantages of optical torque sensor? Low cost, small physical size

26 Define load cell. Load cell are devices that convert force into pressure , which are then measured.

27 Why magneto elastic load cell is also called pressductor load cell?

The degree of change has a direct relationship with the applied stress or force. So it is called pressductor load cell.

28.What are the advantages of magneto elastic load cell?

Extremely robust transducer • Produces relatively high output signal levels • Overload ratings are as high as 15 times the rated loads

29.Write the abbreviation of API scale.

API - American Petroleum Institute

30 Write the disadvantages of bridge type gas densitometer.

The major disadvantage is that the variations in ambient temperature will introduce errors.

31 For what purpose accelerometers are used? • For the measurement of shock & vibration • For gross measurement of acceleration of vehicles like aircraft, submarines etc.

32 What are the advantages of LVDT?

is used for steady state and low freequency vibration measurements. • Smaller amss, so, it is used for the measurement of vibrations of higher frequencies.

33 Define piezo electric effect.

If the dimension of crystal are changed by the application of a mechanical force, an electrical potential appears across the crystal. This effect is called piezo electric effect.

34 What are the features of piezo electric accelerometers?

Small in size and weight • It can be used for vibration and shock measurements. • High output impedence • Their response is poor at low frequencies

35 Define density

It is defined as the mass per unit volume of a substance under fixed conditions.

36 Define specific gravity.

It is defined as the ratio of density of one substance to the density of another reference substance both obtained at same temperature & pressure.

37.What is the other name for specific gravity?

Relative density.

38 Define viscosity.

It is the property of the fluid which gives the resistance to the flow.

39.What are the units of density?

Kg/m3 or gm/litre or gm/ml

40 What are the main parts of an electrical pressure transducer?

(a) Pressure sensing element such as a bellow, a diaphl11gm or a bourdon tube. (b) Primary conversion element. e. g resistance or voltage. (c) Secondary conversion element.

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41 What is the principle of operation of a piezoelectric pressure transducer?

When pressure is applied to a piezoelectric crystal such as quartz, an electrical charge is generated.

42 What are the types of thermal conductivity gauges?

(a) Pirani gauge (b) Thermocouple gauge

43 What is the purpose of ionization gauge? Ionization gauge is used to measure the density of a gas.

44 What is the function of a dead weight tester?

Dead weight tester is used to calibrate bourdon gauges .It is used as a measuring device and also as a calibration method.

45 What are the disadvantages of using thermocouple gauge? (i) Easily damaged by organic vapours (ii) The filaments can be coated with a deposit of devapourised vapours which alters the way the filament transfers heat.

46 Define thermal conductivity

The ability of the material to carry heat by conduction is called as the thermal conductivity.

47 What is a vacuum pressure?

Pressure which are below the atmospheric pressure are called vacuum pressure.

48.What is the purpose of calibrating a pressure measuring instrument?

It is used to adjust the output signal to a known range of pressure. It includes zero, span and linearity adjustment.

  1. What are the disadvantages of LVDT pressure transducer?

Large core displacement are required for appreciable amount of differential output.  Temperature affects the performance of the transducer.  They are sensitive to stray magnetic fields.

50 What is the principle of operation of a capacitive pressure transducer? It is based on the principle of the familiar capacitance equation of the parallel plate capacitor (ie) C=G0GrA/d farad

(ie) capacitance = GA/d G0=8.85*exp(-12)f/m2 Gr=Dielectric constant A ->Area of each plate d->Distance between two plates

51 Define temperature?

The temperature of a substance is a measure of hotness or coldness of that substance.

51 What is the difference between temperature and heat? Temperature is defined as “degree of heat”. Heat is used to mean “quantity of heat”.

52 What are the temperature scales?  Lower fixed point or ice point.  Upper fixed point or steam point.

53 Define triple point?

A particular temperature and pressure at which three different phases of one substance can exit in equilibrium is known as “triple point”.

54 Write some methods of measurement of temperature?  Expansion Thermometer.  Filled system Thermometer.  Electrical Thermometer.  Pyrometer.

55 What are the different types of filled system Thermometer?

Gas-filled Thermometer.  Liquid-filled Thermometer.  Mercury-filled Thermometer.  Vapour-filled Thermometer.

56 Define Seeback effect?

If two dissimilar metals are joined together to form a closed circuit, there will be two junction where they meet each other. If one of these junctions is heated, then a current flow in the circuit which can be detected by a galvanometer. The amount of current depends on the difference in temperature between the two junctions and on the charactSeristics of the two metals. This was observed by Seeback & hence known as Seeback effect.

57 Which effect is used in thermocouple? Seeback effect is used in thermocouple.

58 What is the purpose of protecting tube in a thermocouple? It is used to protect the thermocouple from harmful atmosphere, corrosive fluids and also to prevent from mechanical damage.

59 Explain the principle of operation of thermistor? They have negative temperature coefficient of resistance i.e. with increase in temperature the resistance decreases and vice-versa.

60 What is the drawback in two wire RTD? Two wire RTD’s will give a large lead wire & hence it is impossible for accurate measurement of temperature.

61 Give some examples of the temperature instruments?

Resistance thermometer.  Thermocouple.  Thermistor.

62 Define pyrometry .

Pyrometry is the technic for measuring the body’s temperature by measuring it’s electromagnetic radiation.

63 What are the two types of pyrometer ?

a. Radiation pyrometer b. optical pyrometer.

64 What is the advantage of optical pyrometer?

It is used to measure high temperature.

65 How the calibration is adjusted in optical pyrometer? By adjusting the emissivity.

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