TG Set load fluctuations due to grid 1

[sudiptoghosh]

We have a 18 MW generator running in parallel with the utility grid.The max generation is around 14 MW.After 4MW of internal consumption remaining 10 MW is exported to Grid.
Today it was noticed that thre was a severe hunding in the TG load ie.. from 10 MW it went down to 2 MW and again picked up to 8MW and again 4 MW.(As seen in DCS trends)
There was a variation in the grid frequency also in the range of 50 to 51.5 Hz during that period.After some time the grid breaker tripped on overcurrent and also an reverse active power protection alarm was noticed in the Generator relay panel.However after the tripping of the grid breaker the generator came on home load but during the time the grid breaker tripped many (not all)
motors has tripped in the plant.
Can anybody explain the phenomenan

 

[dpc]

You might want to read up on governor droop settings.

 

[waross]

3% increase in grid frequency causes an 80% load drop. Looks like 3.75% droop on the governor.

Bill
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"Why not the best?"
Jimmy Carter

 

[ScottyUK]

Figure out what mode your governor is operating in. Most modern sets can be configured as any of isochronous, plain droop, constant power, or base load.
There are perhaps one or two other specialised modes required by the TSO as part of the connection agreement, but these are essentially modifications of the main four.


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If we learn from our mistakes I'm getting a great education!

 

[sudiptoghosh]

Thanks for your replies.Actually the droop setting is 4 %.The DCS trends are not so fast to show the actual MW during the disturbance.The frequency had actually gone upto 52.5 Hz momentarily , as understood fron the nearby grid substation.(Two local grid substation was disconnected from the main grid and our Power plant and Wind generation plant of 32 MW started feeding the islanded local grid).Our overfrequency relay was set at 51.5 Hz but with a 2 sec delay.
The plant load is 5 MW only around 300 AMPS(11kv).So how the grid incommer breaker tripped at OVERCURRENT (recorded 2400 amps nearly balanced).Please note that the instance when the grid 11 kv breaker tripped recording a current of 2400 amps, the same time reverse power alarm was actuated in the generator protection relay..If the plant load is 300 amps how come the current has gone upto 2400 AMPS .Was the excess amps due to the reverse power in the generator.Is it possible to draw so high current during reverse power.No fault was found in the plant side and most of the motors were running after islanding.Some motors have tripped probably due to voltage drop due to such high current.
Request your opinion

 

[waross]

You were motoring the generator. Also you were trying to accelerate all your plant motors about 5%.

Bill
--------------------
"Why not the best?"
Jimmy Carter