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[SOLVED] Voltage behaviour during sag events

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Member level 3
Apr 17, 2014
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Some grid codes say that the distributed generation system should stay connected to the main utility during events of low voltage during a short period in accordance with each standard, this is called LVRT. At the same time the inverter should provide reactive power to the main grid during this event.
My questions:
1 - Why should the inverter provide reactive power during the event of low voltage?
2 - What would happen if the inverter does not provide reactive power to the grid during an event of low voltage?

Can't say much about low voltage events. I understand utilities want inverters disconnected from the grid during a blackout.

If your inverter were sending juice onto the grid, it would endanger linemen working to restore power. There is the possibility your AC will be stepped up to even higher voltages, as it goes in reverse direction through transformers.

the amplitude of the grid voltage is related to the reactive power. you can find more detail in the book titled: Reactive power control... (do not remember exact title) by :Miller.
injecting reactive power helps to maintaining amplitude of the voltage and soothes fault condition.

P.S: it's not about black out or long term sag. just for a few seconds depending on the grid standard.

Obviously if available inverters inject the correct reactive and real power into the grid during a sag, there will be less of a sag. However this is desire-able for only a few seconds as the inverter has to continuously test for no mains and dis-connect for reasons of safety, as mentioned above....

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