Reactive Load Bank vs Resistive Load Bank

[ronnied]

Can anyone tell me or point to a white paper that explains when you should spend the extra money for a reactive load bank? What is the chance you will test the genset using a resistive load bank and when you need to start large, (4160v 800hp), motors it fail, etc?

 

[waross]

Hi ronnied
That's a good point about starting large motors. It puts a lot more current stress on the generator windings than a normal load test.
It also lends more support to your desire to use the utility for a load bank.
When you are paralleled with the utility the controls act differently than when the set is islanded.
The load on the set is controlled by the governor setting. More throttle, more load.
The reactive power is controlled by the excitation. More field strength, more VARS pumped back into the system.
When you are paralleled, put the governor in "Droop" mode and
watch your kw output vary instead of frequency as you change the governor setting.
Then vary the voltage control and you will see the current and the KVARs vary instead of the voltage.
Back to the problem at hand;
If you want to prove KVAR capacity you either need a reactive load bank or a connection to the utility.
If you want to prove that the generator will withstand the magnetic and thermal stress of starting large motors you may be able to do a current test.
Short circiut the output of the generator. start it up with no load. Then apply the field manually with a variable source or a manual voltage regulator until you reach the current you want to test at.
I have used this method to dry out a 350 KW set after the hurricane.
When we started we could read the insulation resistance with a multi meter and it was low. We energized the field with a battery charger and got about 50% full load current.
Then we ran it for a day. We brought the insulation resistance up into the megohms.
That was the first set back online at the little power house after Hurricane Mitch.
respectfully