Steam Turbine Governing System

Prepared by: Nimesh Gajjar

DEFINITION OF GOVERNING“A SYSTEM WHOSE PURPOSE IS TO CONTROL A PRIME MOVER”

OR

GOVERNOR IS A DEVICE TO CONTROL SPEED /LOAD TO A SET POINT.

Why Governing is required?• The characteristics of an ungoverned

turbine is unsuitable for electric power generation. The figure shows the characteristics of an ungoverned and a speed governed turbine.

• The turbine output is controlled by varying the steam flow by means of throttling valves of the turbine .The valves are controlled by the governor.

• Governing system is required to ensure that the system demand is followed automatically without large deviation in the nominal electric frequency

* Constant speed at varying extractions and exhaust steam parameters/conditions.

The main purpose of the Governing System is to maintain:

* Constant speed at variable loads.

* Constant speed at varying steam inlet parameters.

SPEED CONTROLLER

Principle methods of load reduction

• Throttle governing• Nozzle control governing• Bypass governing• Combination of the above

• Types of Governors• Mechanical Governors (CENTRIFUGAL FLYWEIGHT )

SPEEDER SPRING

FLY WEIGHTS

SPOOL

ROTATING SLEEVE

SHAFT DRIVEN BY TURBINE SHAFT

Steam Turbine\Governing\Steam-Turbine-Training.swf

OIL PUMP

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CENTRIFUGAL GOVERNOR

LINKAGE

SERVOMOTOR

THROTTLE VALVE

P1C

P0

STEAMGEAR

PILOT VALVE

EXHAUST TO CONDENSER

• HYDRO- MECHANICAL GOVERNOR

• NOZZEL GOVERNORNING

By pass Governing

To produce more power ( when on over load) additional steam may be admitted a by-pass valve to the later stage of the turbine.

HuntingSuppose, if the load on a turbine is suddenly reduced, the machine begins to speed up. When the speed reaches a certain value, the governor comes into operation and due to this the steam supply is considerably reduced with the result that the speed drops well below the normal value. Again the governor acts after a period of time, which depends on a number of circumstances such as friction, sensitiveness etc. and the steam supply is suddenly augmented. Again the speed rapidly rises and the cycle begins a new.

Fluctuating loads or a sudden change of load especially in case of reduction of load, are more likely to produce hunting, but in other cases it will persist even at fairly steady loads.