Conditions to put primaries in parallel for MV 1

[AusLee]

Hi,

Please i looking for the conditions to put the MV side of two exact transformers in parallel.

The sources feeding the trafos are MV generators, started randomly, i must install all the necessary to ensure that as of "the equipment (to be installed)" everything after is safe and everything before can be pure random.

I have something similar to that here if it helps:

http://lndang.tripod.com/parallel.htm

Thanks.

 

[NewfieSparky]

To parallel generators you need three things: same voltage magnitude, same phase angle, same frequency. Also, if you're talking about paralleling after transformers, you may need to address issues surrounding tap changers if they are present. If they are, you must make sure that the two tap changers change tap settings at the same time. Synchronizing check relays or even old time gauges are available and should be used in your application.

Hope this helps

 

[AusLee]

Correction:

the primary of thetransformers are not fed by MV generators.

Each primary is fed from a source 100% indpendent of the other.

I assume that the use of the old time gauge you mentionned is something like: one source is actively feeding the load, the second source (i.e. the one to enter in synchro) is still offline; the control allow to adjust the phases until the gauge marks zero or near 0, then the source enters successfully in parallel with the first. I also witnessed a tentative where the electrician hit the button when the phases were out of sync, the result was a loud "clack" (breaker close) followed by a "vooom" (meters, motors) then a (softer?) "clack" the breaker disconnected: the "system" did not allow the source to enter in parallel. He tried again and next time he gotit well.

I'm asking for the case where the two sources are supplying power, none can be taken offline for "synchro". This is the case where countries share electricity: the 220kV ring from country 1 (stepped down to 66kV) and the local 66kV have nothing in common with respect to phase sequence, yet they mist enter in parallel. I mentionned the trick of putting 1-to-1 "isolating" transformers to ~reduce~ the effects of the entry in parallel, but it does not eliminate the problem.

What can a phase sequence relay do when it monitors two active lines? Futilessly wait forever untill they become "in-phase"?

 

[stevenal]

Since the two systems are not synchronized to the exact same frequency, their will be a slip frequency between them. A sync check relay will monitor the difference in voltage between the two systems until a low value is achieved, and initiate the close. Or use a light bulb and do it manually. If you cannot wait that long, you need an AC-DC-AC link.

 

[AusLee]

Ok, i can't "wait" for something to happen on the network to create favorable conditions for the entry in parallel.

Therefore the AC-DC-AC link is cool, but i don't know any manufacturer - can you please point some? the powers in question are from 2 to 34 megawatts.

Thanks!

 

[ScottyUK]

If you have control of the AVR and governor of at least one of the generators then you should be able to achieve synchronous conditions between the two islands fairly quickly using an automatic synchroniser. This relay will adjust the voltage and phase through raise and lower signals to the generator. A minute to achieve synchronism is a pretty average performance from a synchroniser on a big turbo alternator with a steam prime mover; industrial gas turbines can manage about 20 seconds or so, and small diesel sets can synchronise within just a few seconds. The question now is how fast do you need it? An intermediate DC link running at 30-odd MW is going to be two or three orders of magnitude more expensive than an automatic synchroniser. DC links are useful for interconnecting nations or nation-sized blocks, but it doens't sound like that describes your installation.

Synchronisers are available from most of the big manufacturers: Siemens, ABB, GE, Cummins / Onan, Brush, etc.


----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!