* Short Interview Question Answers on Steam Turbine

Short Interview Question Answers on Steam Turbine

1. What is a steam turbine?
Steam turbine is a high speed rotating machine which converts the heat energy of steam into work energy (motion energy or electrical energy).
2. Why is steam turbine most widely used?
Steam turbines are widely used to develop power as their efficiency is highest as compared to other turbines.
3. Name the various types of steam turbines.
There are two types of steam turbines.
(i) Impulse turbine
(ii) Reaction turbine

4. What is an impulse steam turbine?
Total expansion (total pressure drop) is in fixed nozzles located outside the turbine casing. In this case, velocity of steam from the nozzle is very high. The jet of steam coming out of the nozzle strikes the blades mounted on the rotor. The rotor is connected to the generator and thus produces power. It has been observed that the velocity of steam jet is almost two times the velocity of the moving blades.
5. What is a reaction steam turbine?
In a reaction turbine, nozzles (called as fixed blades) as well as moving blades are mounted on the rotor. There is a pressure drop in the nozzles as well as in moving blades. Pressure drop takes place in stages i.e. total pressure drop does not take place in one set of nozzles. Therefore, velocity of the steam jet is less than that in case of an impulse turbine. Hence number of stages (one stage = set of nozzles (fixed blades) + set of moving blades) will be required to utilize total pressure drop.

6. What is meant by a stage in a turbine?
In an impulse turbine, stage means set of nozzles outside the turbine + moving blades on the rotor.
In a reaction turbine, stage means one set of fixed blades + one set of moving blades.
7. What is meant by degree of reaction?
DEGREE OF REACTION OR REACTION RATIO (ρ)
It is the ratio of static pressure drop in the rotor to the static pressure drop in the stage
ρ = (Static pressure drop in rotor/Total static pressure drop in one stage)
OR
ρ= (adiabatic enthalpy drop in rotor/ Total adiabatic enthalpy drop in one stage)
Degree of reaction has the symbol ρ (row). It has no units.
Degree of reaction in an impulse turbine will be zero.
Hence degree of reaction is applicable to the reaction turbine.
If degree of reaction is greater than 50%, then only turbine is called a reaction turbine.
Larger the degree of reaction, larger will be the efficiency of the turbine. Therefore it helps in the selection of a turbine.
50 % degree of reaction means pressure drop in the fixed blade = pressure drop in the moving blade.

8. What can be the possible reasons for a turbine not developing the designed full power?
The following can be the possible reasons for a turbine not developing the full power:
(i) The supply steam pressure as well as temperature is not as per the design conditions.
(ii) Pressure at exit of the turbine is too high. It should be under vacuum condition.
(iii) Nozzles and blades have partially been worn out.
(iv) The turbine is overloaded.
(v) Steam strainer is blocked.
(vi) Incorrect governor setting

9. What is meant by governing a steam turbine?
Steam turbine governing means controlling the flow rate of steam into a steam turbine to maintain a constant speed of rotation under all loads. The variation in speed can have a significant impact on its performance.

10. What are the different methods of steam governing in a steam turbine?
There are four different methods of governing the turbines.
(i) Throttle governing
(ii) Nozzle governing
(iii) By pass governing
(iv) Combination of (i), (ii) and (iii) methods