208 POWER PLANT ENGINEERING
(iv) Variation in temperature of feed water.
(v) The varying condition of cleanliness of heat absorbing surface.
The efficiency of steam turbines can be increased:
(i) By using super heated steam.
(ii) Use of bled steam reduces the heat rejected to the condenser and this increases the turbine
efficiency.
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-