> From:         carlosmarcano78@cantv.net[SMTP:carlosmarcano78@CANTV.NET]
> Sent:         Tuesday, June 29, 2004 10:46 AM
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      [EE:] Harmonics in a Generator.

> Hi list. I have this little problem I would like to share to see if any of
> you have known of something similar. I work at an hidroelectrical dam, Guri
> Dam (Raul Leoni Dam to be more precise), in Venezuela. I am part of the
> Regulators Section for about 6 months now. We are on charge of the
> excitation systems of the generators among lots of other stuff. We also are
> on charge of the syncronizers of the machines. These devices check the
> phase and voltage coming from a generator (through the step-up transformer)
> and the phase and voltage of the line (the rest of the electrical system)
> and sends the orders to the generator to raise or lower the freq or voltage
> of it to match the system and when these parameters are as close (or equal)
> as posible sends an order to the breaker switches and "syncs" the generator
> with the system, alouding to pump the power from the machine to the system.
> Recently we were having trouble with one of the generators (there are 20
> here, for a total installed capacity of 10.000 MW) when syncronizing (I
> dont know if this is spelled right). It was absorbing a huge amount of
> MVAR, which is ussually and indication of a difference between the
> generators voltage and the system's voltage when syncronizing, difference
> that should not be more than around 1 volt. We calibrated the syncronizer

. . . .

> Instead, we are
> getting a clean, 60 Hz 120 VAC rms signal from the line's side and a pretty
> much like wave from the generator's side but with little peaks         that look
> like harmonic distortion. We got the generator desyncronized (switches
> opened) and measured the signals at A and B again, the B signal (system's
> side) was exactly the same clean one and the other one from the A point
> (generator's side) was more distorted, with a bigger harmonics component.
> The thing is: Is it possible (well it seems like it is!) to see two
> different signals from the same line conection? Isn't the system a "bigger
> voltage source" than the generator so the signal should be the system's
> one? I am a little confused... Hope someone could give me some light in
> this matter. TIA,

> Regards,

>   *Carlos*
> -- Guri, Venezuela --

The harmonic distortion is at a higher frequency than 60 Hz, so it may
not pass through the power transformers as easily as the 60 Hz signal.
That would allow the harmonic signal to exist on one side of the
transformer while the other side was being driven by the "bigger voltage
source".

John Power

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