Power Plant Engineering

6.14 STEAM TURBINE TESTING
Steam turbine tests are made for the following:
(i) Power
(ii) Valve setting
(iii) Speed regulation
(iv) Over speed trip setting
(v) Running balance.
Steam condition is determined by pressure gauge, and thermometer where steam is super heated.
The acceptance test as ordinarily performed is a check on (a) Output, (b) Steam rate or heat consump-
tion, (c) Speed regulation, (d) Over speed trip setting.
Periodic checks for thermal efficiency and load carrying ability are made. Steam used should be
clean. Unclean steam represented by dust carry over from super heater may cause a slow loss of load
carrying ability.
Thermal efficiency of steam turbine depends on the following factors:
(i) Steam pressure and temperature at throttle valve of turbine.
(ii) Exhaust steam pressure and temperature.
(iii) Number of bleedings.
Lubricating oil should be changed or cleaned after 4 to 6 months.
6.15 CHOICE OF STEAM TURBINE
The choice of steam turbine depends on the following factors :
(i) Capacity of plant
(ii) Plant load factor and capacity factor
(iii) Thermal efficiency
(iv) Reliability
(v) Location of plant with reference to availability of water for condensate.
6.16 STEAM TURBINE GENERATORS
A generator converts the mechanical shaft energy it receive from the turbine into electrical en-
ergy. Steam turbine driven a.c. synchronous generators (alternators) are of two or four pole designs.
These are three phase measuring machines offering economic, advantages in generation and transmis-

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STEAM TURBINE
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sion. Generator losses appearing as heat must be constantly removed to avoid damaging the windings.
Large generators have cylindrical rotors with minimum of heat dissipation surface and so they have
forced ventilation to remove the heat. Large generators generally use an enclosed system with air or
hydrogen coolant. The gas picks up the heat from the generator any gives it up to the circulating water in
the heat exchanger.