VARIOUS ENERGY LOSSES IN STEAM TURBINES

The energy supplied to steam turbine is not fully utilized to transform it into mechanical energy. This is due to various losses occurred in the turbine and energy dissipated away from the turbine. The losses which occur in the steam turbines are given below.

1. Losses in regulating Valves :

Steam before entering the turbine passes through the main valve and regulating valves where it gets throttled adiabatically with constant enthalpy. As a result of this, some pressure drop occurs. Thus, some available energy of steam is lost. The pressure drop varies from 3 to 5 % of the inlet steam pressure.

2. Losses due to steam friction :

As stated earlier, friction occurs both in nozzles and blades. In nozzles, the effect of friction is considered by nozzle efficiency. Losses in moving blades are caused by various factors such as impingement losses, frictional losses and turning losses. These losses are taken into account by blade friction coefficient.,

(K = Vb / Vl )

3. Losses due to mechanical friction :

This loss occurs in the bearings, gears and governing mechanisms and may be reduced by proper lubrication.

4. Losses due to leakage :

Leakage of the steam occur between stages and along the shaft at inlet and exit ends of the casing. In Impulse turbines, the leakage occurs between the shaft and the stationary diaphragms carrying losses. In reaction turbines, the leakage may occur of the blade tips.

5. Residual Velocity Losses :

Steam leaving the last stage of the turbine has a certain velocity which presents an amount of kinetic energy that cannot be imported to the turbine shaft and it is thus wasted.

6. Carry over losses :

Some energy loss takes place as steam flows from one stage to the next is given by carry over efficiency.

7. Losses due to wetness of steam :

In multi - stages turbines, condensation of steam may occur in the last stages, since water and steam have different velocities and will not form homogenous mixture. The water particles will have to be dragged along with steam and in doing so a part of kinetic energy will be lost.

8. Losses due to radiation :

As the turbines are heavily insulated, this loss is negligibly small.

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