Are you in a dilemma of how to face the interview successfully? Are you nervous about how the interview session going to be? Do you want to overcome your fears? Then here you are at wisdom jobs online portal which monitors you in a right way. Thermal power plant is power station in which energy is converted into electric power. It is also referred as coal thermal power plant and steam turbine power plant. A coal based thermal power plant converts the chemical energy of a coal into electrical energy. The role of a power plant operator is to control the power-generating equipment to generate electricity. So, trace your career as power plant operator, power plant engineer, mechanical engineer, turbine engineer, assistant plant engineer, service engineer, boiler engineer and so on by looking into thermal power plant job interview questions and answers.
Question 1. What Are The Main Circuits In The Thermal Power Plant?
Answer :
Thermal Power plant consists of four main circuits, they are:
Question 2. Steam Power Plant Works On Which Cycle?
Answer :
Steam power plant works on the principle of Rankine Cycle.
Question 3. What Is The Thermal Efficiency Of Steam Power Plant?
Answer :
Thermal efficiency of steam power plant is defined as the ratio of heat equivalent of mechanical energy transmitted to the turbine shaft to the heat of combustion. Generally Thermal efficiency of the steam power plant will be in the range of 30-35%.
Question 4. What Is The Overall Efficiency Of The Thermal Power Plant Or Steam Power Plant?
Answer :
Overall efficiency of the system is defined as the ratio of heat equivalent of electrical output to the heat of combustion. Generally Overall efficiency of the steam plant will always be less than the thermal efficiency of the steam plant, it will be of the order of 29-33%.
Overall efficiency of steam plant is determined by multiplying the thermal efficiency of the plant with efficiency of the generator (electrical efficiency).
Question 5. Why The Thermal Efficiency Of The Steam Power Plant Is Quite Low?
Answer :
In Steam power station, more than 50% of the total heat of combustion is lost as heat rejected to the condenser and the loss is unavoidable as the heat energy cannot be converted in to mechanical energy with out a drop in temperature. Steam in the condenser is at lowest temperature. This is the reason that the thermal efficiency of the power plant is quite low.
Question 6. On What Factors Efficiency (thermal) Of The Steam Plant Depends?
Answer :
Efficiency of the thermal plant depends on three factors, they are
Thermal efficiency increases with increase in temperature and pressure of the steam entering the turbine. For this reason high temperature and pressure are used. Thermal efficiency is effectively increased by decreasing the pressure in the condenser, so pressure in the condenser is kept as low as possible.
Thermal efficiency also increases by reheating the steam between turbine stages.
Question 7. Why Efficiency In Thermal Power Plant Is Low?
Answer :
Almost 50% of the heat generated is lost at the condenser as heat rejection. It is unavoidable as with out heat rejection it is not possible to convert heat energy into mechanical energy and drive the turbine without drop in temperature. Therefore majority of the loss takes place in the condenser. Thus efficiency of the thermal power plant is between 30-35%.
Question 8. On What Cycle Does Thermal Power Plant Operate?
Answer :
Thermal Power plant works on the principle of Rankine cycle.
Question 9. Why Generation Voltage In Thermal Power Plant Is Between 11kv To 33kv?
Answer :
The current carrying conductor cross section depends upon the magnitude of the current it is carrying and insulation strength of the conductor depends on the maximum voltage it can withstand. Therefore while designing the generator an optimum value is chosen between the amount of the current and voltage conductor can withstand.
Question 10. How Efficiency Of Thermal Plant Can Be Improved?
Answer :
Some of the methods by which the efficiency of the thermal plant can be improved are:
Question 11. Advantages And Disadvantages Of Thermal Power Plant?
Answer :
Advantages:
Disadvantages:
Question 12. What Is Cavitation And Disadvantages Of Cavitation?
Answer :
The formation of air bubbles and water vapour on the water surface due to the reduction in the pressure is called "Cavitation". When the pressure on the water reduces below the saturation pressure corresponding to the temperature of the water, the rapid formation of the water vapour and air bubbles starts. The bubbles suddenly collapse with the violent action and this collapsing pressure will be very high. The rapid formation and collapsing of bubbles causes the pitting of the metal surface. Cavitation also reduces the efficiency of the hydraulic prime mover causing the honey-combing of runner and blade contours which reduces the power output.
Question 13. What Is The Largest Pump In The Thermal Power Plant?
Answer :
In thermal power plant Boiler Feed Pump (BFP) is the largest pump, it delivers the water to the boiler.
Question 14. What Are Different Types Of Steam Boilers Used In Thermal Power Plants?
Answer :
Different type of boiler used in thermal power plants are:
Question 15. What Are Different Types Of Pulverizes?
Answer :
Different types of Pulverizers are:
Question 16. What Is The Purpose Of Pulverizes?
Answer :
Pulverizers serve two purposes, to dry the coal and to grind the coal. They crush the coal to size of 74microns.
Question 17. What Are The Different Auxiliary Systems In Thermal Power Plant?
Answer :
Coal handling and storage, coal pulverizes water treatment plant, steam boiler, Drought systems, Ash Handling systems, Steam turbine, Circulation water system, Electrical Systems, Control and Instrumentation, Pollution Control equipment, and Fire Protection System.
Question 18. What Type Of Cooling Is Provided For Generator In Power Plant?
Answer :
Hydrogen gas cooling is employed for large size generators because of better heat carrying ability of the hydrogen. Hydrogen cooling is provided for rotors and core of the generator. Water cooling is provided for the stator of the alternator.
Question 19. What Are Different Types Of Circuit Breakers Employed In Thermal Power Plant?
Answer :
For low voltage operation 415/220V vacuum circuit breakers or air break circuit breakers are employed. For voltage ratings about 6.6kV and beyond SF6 circuit breakers are employed.
Question 20. How Generator Transformer Is Cooled In Thermal Power Plant?
Answer :
MVA power rating of the Generator Transformer will be equal to the alternator. Hence lot of heat will be generated while generator transformer is under operation. Oil Forced Air Forced (OFAF) type of cooling is employed for generator transformer.
Question 21. What Are The Different Generator Protections Employed In Thermal Power Plants?
Answer :
Faults in the windings, Over load protection, Over heating of windings or bearings, Over speed protection, Loss of Excitation protection, Motoring operation protection, Inadvertent energisation, single phase or unbalanced current protection, out of step operation protection, sub-synchronous oscillations protection and earth fault protection.
Question 22. What Are The Major Electric Systems In Thermal Power Plant?
Answer :
Major electrical equipment in thermal power plant are
Question 23. What Is The Difference Between Safety Valve And Pressure Relief Valve?
Answer :
Difference between safety valve and relief valve
Relief Valve: The relief valve is used on a filled vessel. For such a valve the opening is proportional to increase in the vessel pressure. Hence the opening of valve is not sudden, but gradual if the pressure is increased gradually. A relief valve is meant to relieve pressure to prevent an over pressure condition. A relief valve may have an operator on it to assist in opening the valve in response to a control signal. The capacity of PRV are generally small.
Safety Valve: This device is used to relief on a compressible filled vessel. For such a valve the opening is sudden. When the set pressure of the valve is reached, the valve opens almost fully. A safety valve is meant to relieve pressure without operator assistance and a safety valve, or combination of safety valves, must be have a capacity to relieve more than the energy input to the volume being protected.
Question 24. What Is Pressure Relief Valve(prv) ?
Answer :
Image of pressure relief valve.
The relief valve (PRV) is a type of valve used to control or limit the pressure in a vessel or system during an overpressure of the system. The primary purpose of a pressure Relief Valve is protection of life and property by venting fluid from an over pressurized vessel. Many electronic, pneumatic and hydraulic systems exist today to control fluid system variables, such as pressure, temperature and flow. Each of these systems requires a power source of some type, such as electricity or compressed air in order to operate.
A pressure Relief Valve must be capable of operating at all times, especially during a period of power failure when system controls are nonfunctional. The PRV is provided on the on the main steam line to control the line pressure. The PRV is generally operated through pneumatic pressure.The PRV operated according to the set pressure of rhe controller. The valve set down when the pressure reach to normal value.
Question 25. What Is (nrv) Non Return Valve?
Answer :
This is also known as one way valve which allow the fluid flow in one direction only. As its name implies non return means there is only one direction flow.All the assembly are provided with a valve bonnet.This valves are generally used in pump discharges and steam water pipe lines.This device ensures there is no back flow of fluid from the source. It has two lines one is inlet line and other is outlet line.There is a direction symbol provided on the valve which show the direction of flow fluid.
Types of NRV:-
Question 26. What Is Steam Trap And It's Function?
Answer :
function of steam trap- It is a device is used in steam pipe line to discharge condensate and gasses, prevent to escape of steam through the line. It ensures that steam is not wasted. This is a self contained valve which automatically drains the condensate from a steam containing device. This is generally provided in steam drains or before steam drain valve.
Types of steam trap:-
Question 27. What Are The Methods Are Used For Steam Temperature Control In Boiler?
Answer :
We can control steam temperature by :
Question 28. What Is The Effect Of Soot Deposits In A Boiler?
Answer :
Question 29. What Is Priming Of Boiler ?
Answer :
It Is the carrying amount of droplet water in the steam, witch leads to carryover of Salt crystals on the super heater and turbines. priming may be caused due to sudden change of load and maintaining of high level of water.
Prevention of priming and foaming:
The best remedy for foaming and priming carryover is the proper blow down of TDS. The continuous blow down should be regulated to maintain the TDS at 3,000 to 4,000 ppm. More blow down means less TDS but more blow down is the more loss of the boiler so the blow down should be within control level.
Question 30. What Is Foaming Of Boiler?
Answer :
It is the generation of foam In boiler due to high concentration of solids, organic matter, bubbles are build up on the surface of boiler water and passed out with the steam. This is generally caused due to high concentration of solids in boiler.
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