Load Change on Free Governor

Speed change create mechanic torque change depend on speed droop, governor function and energy reserve.

On the free governor mode (co-ordination control mode between turbine and boiler control), change turbine or generator speed in dead band area as frequency change, the Turbine Control valves are still stand still. The opening of Turbine Control valves only change while the frequency is outside from dead band area. Dead band is using ti prevent the control valve get hunting.

The picture above describe that if signal from turbine side is zero can say free governor mode and no other signal input (turbine valves position and boiler firing rate), frequency change only from external load change.

Please visit Turbine Governor Control for previous explanation.




































Case:
The system consist 4 unit generator which capacity 500MVA total supplying 1200MW and frequency 50Hz. Inertia constant for each unit is 5s base on 500MVA. Variation load 1,4% for 1% frequency change or damping constant 1.4.
While the load suddenly decrease 50MW, how much change of frequency?

For 4 unit base on 200 MVA,
Inertia constant H = 5 x ( 500/2000)x4 = 5 so M=2H =10s
Remain load (1200 – 50) = 1150 MW
Damp constant D = 1.4 x (1150/2000) = 0.805%

This is Laplace Transform for (s) to (t) function.






























Please visit Turbine Governing System http://idpowerstation.blogspot.com/2009/09/turbine-governing-system.html

Or visit about Load Shedding http://idpowerstation.blogspot.com/2011/12/load-shedding.html