Hydraulic governing system of centrifugal (speed) governer type is adopted in turbine.
Sensitive oil pressure to actuate centrifugal governer is 6.1 kg/cm2 (max). At 6.7 kg/cm2 relief valve is attached for on load testing.
Relay oil at pressure 21 kg/cm2 (max) is used to actuate HP CIES valve, governer valve, LP CIES valve and LP governer valves.
At speed of 2560-rpm governer system becomes effective and starts draining of sensitive oil to 2.81 kg/cm2 as speed is 2760 rpm and this is the governer take over speed. Once the speed takes over by governer, governer valves position comes to closing side and then CIES valves are opening fully. At this stage further opening of CIES valve does not change any speed of system and the speed depends only on governer valve opening position and speeder gear system.
HP speeder gear controls HP governer valves and LP speeder gear controls LP governer valves and closes fully when 6% over speed which starts when 3% over speeding.
The main purposes are as follows.
a. Bring the TG to rated (synchronous speed) speed from rest.
b. Loading and unloading when synchronised.
c. Responding with grid frequency variations within design rage and loading and unloading the machine so that grid frequency remains stable.
d. Limiting the load as per reactor load.
e. Protecting the machine from over speed and from sudden large load thrown off or trip.
f. Tripping the machine and bringing it on barring gear when event for not operation happens.
g. When synchronised the speed is regulated by speeder gear from BPC signal. Once synchronised the grid frequency and speeder gear controls the speed.