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'[EE:] Harmonics in a Generator.'
2004\06\29@104631 by osmarcano78

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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
and adjusted the sync times (he syncro should take in count the switches
and all the relays between them and the syncro when sending the sync
signal). Everything was ok, until we took in count that when registering
the signals from the generator's side and the system´s side after
syncronizing and realized that the signals where different! I am attaching
a little, simplified drawing of how is the system arranged and where the
signals are measured (points A and B). I assume that the signal should be
the same in both points after syncronizing because it is like having two
voltage sources in parallel, but that´s not happening. 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 --

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'[EE:] Harmonics in a Generator.'
2004\07\02@032101 by Morgan Olsson
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Carlos Marcano 01:55 2004-07-01:
>TCT (Capacitive transf)

= capacitive voltage divider?

High voltage   o----||---+---||---o GND
                         \out

/Morgan
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Morgan Olsson, Kivik, Sweden

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2004\07\08@131555 by Carlos Marcano

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De:  Ken Reid

>32 years with machines ranging in age from 70 years to 30 years.  A lot of
>change in the last two decades. Retired now

Great, lot of experience! I have just begun here (6 months) and it´s been
amazing. I have learned and seen so many things these last months. Here we
have some old machines also, most Mitsubishis (80´s), Canadian GE(80´s) and
three "antique" Westinghouse generators (from the 60´s). We are involved in
major overhauls at the turbines and gobernor systems and in the next couple
of years we will work on the excitation systems.

Regards,

*Carlos*
--Guri, Venezuela--
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2004\07\08@150444 by Hopkins

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*Carlos*
--Guri, Venezuela--

Did you fix the problem with harmonics?

Roy


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2004\07\09@001758 by Ken Reid

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Hi Carlos,
   Yes, many changes. Stainless wheels thinned out to pass more water and
develop 25% more power (and more welding).  High pressure low volumn
governors. Static exciters. Scada -data aquisition. Digital relays. The new
relaying is much better. Parts from all over the world. Just as you have
learned all there is,  the technology changes, the heads hurts!

Your river with 20 units is five times the volumn of ours. We have to build
multiple plants per river. Costs have become too high now, so they have gone
to upgrading and conserving.

Cheers,
Ken
west coast Canada

{Original Message removed}

2004\07\12@180345 by Carlos Marcano

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De:  Hopkins

>Did you fix the problem with harmonics?

I wish!  We made some measurement from the generator´s output (through
potential transformers) including THD and we found some little distortion on
the waves and 0.8% THD from phase-phase and 3.1 in phase-ground. We havent
had the chance to check the TCT´s now ´cause we have been busy with A LOT of
other stuff but I think next week we will get our hands on them (even now
that we have found some trouble from the generator's side, but we wanna
check everything). Thanks for asking!

Regards,
*Carlos*
--Guri, Venezuela--


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2004\07\12@180346 by Carlos Marcano

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De:  Ken Reid

>Hi Carlos,
>    Yes, many changes. Stainless wheels thinned out to pass more water and
>develop 25% more power (and more welding).  High pressure low volumn
>governors. Static exciters. Scada -data aquisition. Digital relays. The new
>relaying is much better. Parts from all over the world. Just as you have
>learned all there is,  the technology changes, the heads hurts!

 Yes, I know what you mean! Well thats the price of evolution :)

>Your river with 20 units is five times the volumn of ours. We have to build
>multiple plants per river. Costs have become too high now, so they have
gone
>to upgrading and conserving.

 Yes we are very lucky. The Caroni river is one of a kind. It has a great
volume of water and its slope is excelent to get lots of potential. EDELCA
(the company I work for) has built three major dams in this river: Guri (the
biggest, with around 10000 MW - 20 units), Macagua (with 14 working units
with 2540 MW total) and Caruachi the newest with 12 units and 2160 MW. There
is the developing and next construction (finished in 2012) of another one,
Tocoma, with the same characteristics as Caruachi. These dams are located in
what is called the "Bajo Caroni" or Low Caroni. Studies had been made and
there are great chances that we´ll built more hidroelectrical dams in the
"Alto Caroni" (or Upper Caroni). Nature have been very kind with us, so we
must take advantage of that!

 So Ken, whats your specialty; hidraulics, mechanics, instrumentation?


Regards,
*Carlos*
--Guri, Venezuela--

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