Turbine Power Plants Interview Questions and Answers:

1. What for a starting motor is required in a gas turbine power plant ?

Ans. An electric motor is required for starting the compressor, which is required to be started before starting of turbine.

2. Why are majority of gas turbine power plants employed as peak load plants ?

Ans. Gas turbine power plants are usually employed as peak load plants because these plants can be started and loaded quickly and their initial costs are small but fuel costs are high.

3. Why coal and peat are not used as fuels in gas turbine power plants ?

Ans. Coal and peat are not used as fuels in gas turbine power plants because of coal handling and ash handling problems.

4. Why is it advantageous to use high pressure turbine for driving compressor and low pressure turbine for driving alternator in gas turbine power plants ?

Ans. High pressure turbine is used for driving compressor and a low pressure turbine is used in driving the alternator because this arrangement has the advantage that the speed of the power turbine (the turbine driving the alternator) can be kept constant at synchronous speed while the speed of the turbine driving the compressor can be varied according to the output required.

5. Why the efficiency of open cycle gas turbine power plant is quite low ?

Ans. The overall efficiency of the open cycle plants is very low as a greater part (around 65%) of the power developed by the turbine is used in driving the compressor. The fact that the hot gases from the combustion chamber are cooled to a safe temperature before admitting it to the turbine, also reduces the efficiency. The overall efficiency of the plant, owing to above reasons seldom exceeds 20%.

6. How can the thermal efficiency of a simple gas turbine power plant be improved ?

Ans. The efficiency of a simple gas turbine power plant can be improved by employing regenerator, intercooler and reheater.

The regenerator utilizes the heat of exhaust gases to heat the compressed air before it is sent to the combustion chamber, reduces the fuel consumption of the plant and improves the thermal efficiency.

The intercooler is heat exchanger which cools the partly compressed air in order to reduce volume and increase density. The intercooling results in improvement of thermal efficiency.

Reheating improves the output from the turbines due to multiple heating in the same way as intercooling improves the performance of the compressor.

7. In what respects gas turbine power plants are inferior to steam power plants ?

Ans. The drawbacks of gas turbine power plants over steam power plants are:

1. The operating costs of a gas turbine power plants are much higher than those of a steam power plant.
2. Gas turbines can be employed only in small sizes (about 50 MW or so).
3. Like steam turbines, the gas turbine is not readily reversible.
4. In case of a gas turbine power plant, the compressor has to be started before starting of turbine and the former requires power from some external source.