exciter Peak Rating

[HamidEle]

We are running a motor starting study using ETAP. The study indicates the generator generates more Vars than rated. Is that because overxecitation of the generator? But theoretically the generator should be underexcitated. Generator output voltage is 110%. I am wondering if the settings of the generator is proper.

Appreciate if any inputs.

 

[ElSparky]

Hi

Not sure if I understand you correctly.
However if you run your Generator with 110% Rated Voltage you will supply VAR to the Grid. Assuming that you are connected to a grid off course and that the Grid voltege is less than 110% rated.

So you are right. Overexciting a Generator on Grid will push up the Voltage on its terminals and hence pushing out VAR.

 

[ElSparky]

Hi

Not sure if I understand you correctly.
However if you run your Generator with 110% Rated Voltage you will supply VAR to the Grid. Assuming that you are connected to a grid off course and that the Grid voltage is less than 110% rated.

So you are right. Overexciting a Generator on Grid will push up the Voltage on its terminals and hence pushing out VAR.

 

[waross]

If you are islanded:
The load determines the power factor. The power factor may improve with some types of loads.
The throttle position determines the frequency.

If you are in parallel with the grid:
The excitation determines the power factor. Increasing excitation exports more VARs.
The throttle position determines the KW output.

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

 

[HamidEle]

Just during motor starting periods, the generator will try to import Var to the system to keep the voltages high. That's why we always see the overexcited generator during motor starting.

 

[waross]

Hello Hamid
Those VARs are probably going to the motor rather than to the system. Motor starting current is highly reactive, hence low power factor and high VARs.

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

 

[ScottyUK]

The generator won't import vars, the load will require more vars than the generator can deliver and the excess will be met by the system, causing your installation to present a net negative PF.


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

 

[HamidEle]

The generator does generate Vars and compensate the low power factor during motor starting through excitation system. But it has its limitation.