GOVERNING SYSTEM OF STEAM TURBINE

• Governing system is a device or combination of different system & logics which are used to control the speed of a steam turbine.
• A governor protects the prime mover from over speed & keeps the prime mover speed at or near the desired RPM.
• When a prime mover drives generator supplying electrical power at a given frequency, a governor must be used to hold the prime mover at a speed that will yield this frequency.

THE PURPOSE OF THE GOVERNING SYSTEM

• To regulate the turbine speed till the unit is synchronized with the help of speed governing.
• To regulate the load on the unit as per the Load Limiter setting after the unit synchronization with the help of load governing.
• In both case speed & load is controlled by control valve opening & closing which regulate the steam flow in turbine as per demand.

• For opening & closing of control valve servo motor or power pistons are used which are operated under high pressure governing oil.
• There are two types of oil system is used for governing system
  • Low pressure oil system (18 to 22 kg/cm²)
  • High pressure oil system (160 kg/cm²)
• For both oil system a governing logics are used.

FUNCTION OF TURBINE GOVERNING SYSTEM

Following operation is achieved by turbine governing system installed.

• Thus it can be understood that the Stop Valves and Control valves of the HP Turbine and IP Turbine are to be opened to roll the turbine, and the Control Valves opening is to be varied to regulate the turbine speed till the unit is synchronized
• To regulate the steam admission to the turbine, during load raising & load variations to suit the grid demand.
• Turbine will be tripped through the governing system only on the initiation of the Turbine / Unit Lock out Relay.
• Modern governing system taken place the Electro Hydraulic Governing System (EHTC) is also installed along with the Conventional Hydraulic Governing System.
• For tripping the turbine on the initiation of the Turbine trip relay, trip command will be sent to the Turbine Trip Solenoid Valves and consequent to the actuation of these solenoid valves the ESVs will close first and then the control valves will close and the Generator Circuit Breaker will be tripped, thus isolating the unit from the grid.
• After the unit tripping the unit will coast down to the barring speeds of 120 rpm and continue to run at this speed where the jacking oil pumps are available to keep the machine floating on jacking oil pressure.

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