Load Dump on Diesel Generators

[HarlanLSU1]

I have two 2500KW generators online in parallel. If I trip the generator breaker on one thus forcing the other generator to take on greater than 100% rated load what type (KW,KVAr) of load, or combination of, would be best to put on the generator. I believe a power factor less than .8 would be best to stay away from the excessive rotor heating limit, but would something closer to a pf of 1 be better.

The problem I found was that the generator was not able to recover with the high demand of 3100kW it leveled off at 2620kW at 56.15HZ. However, it was able to fully recover within 2sec with 2850kW (same power factor, using load banks). The point of this testing is to initiate load shedding stages.

 

[waross]

The power factor will not make much difference to the engine loading. I would be programing my load shedding so that in the event of the trip of a generator breaker or loss of one generator, the system would immediately shed non essential loads. The ability to recover from a block overload may vary depending on the ambient temperature, atmospheric pressure, relative humidity, and fuel specific gravity. The overload capacity past rated load will also degrade with time as the engine wears.

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

 

[peebee]

Or you could use a frequency relay with time delay for load shedding.

 

[HarlanLSU1]

Thank you both for your response. We have been load shedding in two stages non-essential and then semi-essential at 2750KW for each. The problem occured when the 3100KW load was seen by the one generator it was not able to recover (actually leveled off at 2620kW) to that load shed mark. It's funny that you say that PeeBee since we are looking into using the existing EPM's to initiate load sheds in certain conditions under so long of a UF condition.

 

[wayne440]

Is a 3100Kw load on a 2500Kw rated set a reasonable expectation? (I have no experence with sets in that size range)

 

[catserveng]

It depends, if these are Standby or Emergency rated machines, it is likely you have little on no overload capability. If these are Prime rated then they would likely have about 10% overload capablility.

As Bill pointed out above, overload capacity is affected by a number of issues, and newer machines meeting US and other countries emissions standards make it unlikely you have lots of reserve capacity.

What does the engines manufacturer say?

The engine may exhibit differnet abilites to respond to the load changes due to turbo performance, also need to make sure there isn't a parameter in the ECM (likely this is an electronically controlled engine ?) that is limiting the fuel after it sees an apparent overload.

 

[rbulsara]

Under-frequency is the correct parameter to use for load shedding.

wayne440:
3100kW is not a reasonable expectation on a 2500kW machine or for any machine. Exceeding the rating will cause under-frequency conditions.

Rafiq Bulsara

http://www.srengineersct.com