Generator MVar Capability Testing

[Bekza]

Hi

What is the impact of conducting MVAr capability test on the generator to prove the the ability of MVAr expoting to the system against the OEM supplied capability diagram. I will push the machine to the rated MVar and keep it constant for about three hours during that time verything must be stable incl temperature etc.All will be done within machine cabapility. Is there a place where i can get info on how to go about doing the test and other safety aspect i need to consider.

Any davice will be appriciated.

 

[GTstartup]

Just bear in mind that the OEM generator capability chart is valid for rated voltage only. It must be adjusted for any deviation from nominal. which will surely be the case if you are at the upper limits of the voltage regulator. Another problem is that you might hit that upper limit before you hit the overexcitation limit, depending on how "stiff" the system is. In theory increasing excitation would result in only an increase in reactive power but in actuality you will get a combination of increase in generator voltage and reactive power. As far as how to do it, this is just an operator function and can be done by an increase in voltage setpoint or by setting the power factor or MVAR to the desired level, assuming you have either PF control or MVAR control.

Things to watch for - V/Hz relay and Overvoltage Relay and depending where you are on the power chart, either stator heating or rotor heating.

 

[ScottyUK]

The GSU transformer may be your ally for this test. You should be able to push the machine to the limit of its reactive loading by judicious use of the tapchanger to add reactive load to the unit.


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Sometimes I only open my mouth to swap feet...

 

[rcw retired EE]

Bekza- GT Startup & Scotty have great points.

MVAR testing is very dependant on system impedance and voltage levels. As you push out MVARS, the generator voltage will rise and so will your in-plant auxiliary voltages and utility system voltages. I usually run into voltage problems long before I reach the maximum point on any capability curve. I have dumped two province wide power systems trying to get the utility system voltage low enough so the power plant could push MVARS to pass the test.

If you have two generators in parallel you may be able to push MVARs from one and absorb some in the other, being very careful to watch the under excitation limits and the typical +/-5% voltage range on the generators.

If you have a good load flow computer model of the system you could do some quick checks to determine the practical voltage or MVAR limits.