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Reverse kVar protection of genset

Reverse kVar protection of genset

Reverse kVar protection of genset


May I seek some advices about the reverse kVar protection: is diesel genset normally equipped with reverse kVar protection?

RE: Reverse kVar protection of genset

More info needed. IS the diesel connected in parallel with power grid or other generators?

RE: Reverse kVar protection of genset

In a paralleled set, the VAR production and direction of a individual set is controlled by the voltage setting of the AVR.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Reverse kVar protection of genset

You might do some searching on "loss of field" protection and "generator capability curves".

RE: Reverse kVar protection of genset

Generator doesn't take-in VArs unless there is problem with its excitation.
Hence, Reverse kVAr protection can be called Loss of excitation or field failure protection in other words.
But, reverse kVAr is possible only when there is kVAr source external to the generator - power grid or a transformer incomer paralleled at the same LV bus etc.

RE: Reverse kVar protection of genset

@ thermionic1

We have 2 cases: 1. single genset not connecting to grid any time. 2. multiple parallel gensets, also not connecting to grid any time.


RE: Reverse kVar protection of genset

Reverse VARs are the result of under excitation.
With a single set, under excitation results in under voltage.
With a paralleled set, under excitation results in reverse VARs.
See dpc's post. "Loss of field" or "under excitation" protection.

Ohm's law
Not just a good idea;
It's the LAW!

RE: Reverse kVar protection of genset

Quote (RRaghunath)

Generator doesn't take-in VArs unless there is problem with its excitation.
In my experience that does not hold for all cases.
Its entirely possible to have an islanded power station with at least one feeder providing VArs. Depending on the loading of the feeders and the overall station its possible to have an export of watts and import of VArs, although this is likely not a condition that would occur very often, perhaps one or two sites out of thirty three as a matter of perspective. If your intent is to detect a loss of excitation, noting that its possible for an import of VArs to occur under certain normal operating conditions then that is more accurate.

However, the value of the protection depends partly on what you're protecting and partly what you want to happen when a condition such as loss of excitation occurs. If we're dealing with supplying an islanded network with no other sources, then;
Single set, any reverse VAr protection must be set with consideration of whatever the VArs of the load need to be so that it only trips at a point where loss of excitation is likely. If excitation is lost or failing badly then undervoltage should also pick up.
Multiple sets, then the other sets will have to both supply VArs for the load and to excite the set with failed excitation. Voltage protection won't pick up as the other sets will keep the voltage in line, as per what waross has said. Depending on the characteristics of the load it may provide benefit, but not necessarily enough to look to implement it by itself if not fitted.

The case in point above, the station ran happily for a number of years without the reverse VAr protection on the sets, and no knowledge of the VAr loading of the feeders. New controllers were fitted, including reverse VAr protection, and a number of trips ensued before the settings were reviewed and it was discovered that under certain light loading conditions one of the feeders went capacitive.

EDMS Australia

RE: Reverse kVar protection of genset

Thanks all for the valuable advices!

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