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This is with reference to a Combined cycle power plant with two GE Gas Turbines, one steam turbine and the customer is the grid. There were two isolated incidents and the speed variation behaviour in the both cases were different
Issue-1- House load Condition
Both the outgoing lines breakers opened and Gas Turbines continued to operate with breaker in closed condition sharing between them a house load of 6 MW. Frequency mantained at 50 Hz. Selection remained on droop and preselect load (With about 65MW load set point).
On attempting for further loading ( manual speed/ load raise command ),GTGs generator frequency did not cross 50.8Hz.( This operation was attempted thinking machine have off loaded unaware about Line breakers tripping).
On attempting to lower the speed (manual speed/ load raise command), GTGs speed could not be lowered than 3000rpm. (This was done to synchronise the Generator directly with the line.)
Issue -2 Islanding Condition
Some other day the plant came into islanding mode. It was running at a load of 214MW and
suddenly load dropped to 168MW because the extended substation to which lines are supplying got isolated from Grid.
Here again assuming a load throw off, tried to increase load.Already frequency has increased due to load throw off. The action has increased the frequency to trip level of 52.0 Hz. This has
resulted in tripping of the units.
My point is how the machines frequency behaved differently in both the cases and I am looking for possible answers for the below questions- 1)Why the first case the frequency did not raise beyond 50.8Hz where as in
second case frequency rose beyond trip level?
2)Why in the first case frequency did not go below 50 Hz?
3)Is the Mark-V control system which was causing this kind of behaviour?
There is no input of Line breaker status to MarK V system.
Hari
Issue-1- House load Condition
Both the outgoing lines breakers opened and Gas Turbines continued to operate with breaker in closed condition sharing between them a house load of 6 MW. Frequency mantained at 50 Hz. Selection remained on droop and preselect load (With about 65MW load set point).
On attempting for further loading ( manual speed/ load raise command ),GTGs generator frequency did not cross 50.8Hz.( This operation was attempted thinking machine have off loaded unaware about Line breakers tripping).
On attempting to lower the speed (manual speed/ load raise command), GTGs speed could not be lowered than 3000rpm. (This was done to synchronise the Generator directly with the line.)
Issue -2 Islanding Condition
Some other day the plant came into islanding mode. It was running at a load of 214MW and
suddenly load dropped to 168MW because the extended substation to which lines are supplying got isolated from Grid.
Here again assuming a load throw off, tried to increase load.Already frequency has increased due to load throw off. The action has increased the frequency to trip level of 52.0 Hz. This has
resulted in tripping of the units.
My point is how the machines frequency behaved differently in both the cases and I am looking for possible answers for the below questions- 1)Why the first case the frequency did not raise beyond 50.8Hz where as in
second case frequency rose beyond trip level?
2)Why in the first case frequency did not go below 50 Hz?
3)Is the Mark-V control system which was causing this kind of behaviour?
There is no input of Line breaker status to MarK V system.
Hari