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Exciter AVR Problem
MVAr power inverted but active power is correct
1 out of 1 members thought this post was helpful...

Hello folks,

I am experiencing something crazy with a AVR controlling a 12,5 MVA generator in a petrochemical plant.

When I am sending +Exc order from the local screen of the excitation cabinet the Field current and the stator voltage increase but the MVAr power decrease. We noticed the opposite for -Exc order, the Field current and stator voltage decrease but the MVAr power increase.

Excitation and protection cabinet are both new.

At first, I thought that the CT coming to the AVR was inverted, but it doesn't make sens because we should have a negative active power too.

In my opinion a 180 on the CT's would impact both active and reactive power. I checked the active power on the protection relay which are not measured by the same set of CT's and we are in line with the Active power measured by the AVR.

When the unit is synchronised while in Voltage regulation mode the system work even if the reactive power is inverted. However, if we switch in MVAr regulation the system goes crazy as the MVAr power measured will never reach the setpoint. It's going in the wrong way.

If someone already experienced such matter, please feel free to share your experience.

Thank you.

0 out of 1 members thought this post was helpful...


It would be extremely helpful if you provided information about the manufacturer and madel of the excitation system in question.

Is it possible that the configuration for the VAr signal is inverted? (I'm presuming the AVR has software-configurable parameters--but without knowing anything about the AVR it's impossible to say much more.)

What gas the supplier of the new excitation system said about the problem?

Are you certain the VAr input signal to the AVR comes from a PT/CT connection, and not from a VAr transducer (4-20 mA transducer)?

Without knowing anything about the exciter and how it is configured and what it's inputs are , nothing more can be said.

Please write back with more details and let us know what you find!

1 out of 1 members thought this post was helpful...


My first thought is core[over] saturation.
Have you looked into this?

Without generator and AVR's all swag.


The excitation system is a Controgen P320 V3 from Alstom.

As far as I know the reactive and active power are calculated by the AVR thanks to the CT's and VT's measurements. I don't see any wires unless CT/VT that could be reversed. That's the problem.

I don't get why a CT saturation would give a inverted reactive power?
Please could you detail.

The generator core! If too much excitation is applied, a point of saturation can occur, which can produce the effect you described.

>I don't get why a CT saturation would give a inverted
>reactive power?