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OLTC fooled by DG's

OLTC fooled by DG's

OLTC fooled by DG's

(OP)
One our single DESN station has x number of feeders and about 40MW load. There are 3 solar generations to be connected to 2 feeders and total maximum output from PV's are about 30MW. Some voltage problems may occur because the OLTC LDC might be fooled by the DG's since it may only see 10MW net load and lower the transformers tap, therefore, some heavily loaded feeder may have low voltage problems.

Any one has some ideas to solve the problem? Thank!

RE: OLTC fooled by DG's

Trying to use load drop compensation (LDC) with bus regulation, where the feeders are very dissimilar will lead to problems.  You can't get much more dissimilar than in your situation.  I suggest you forget about LDC.  Set R=0, X=0 and maintain a constant bus voltage regardless of load.
 

RE: OLTC fooled by DG's

Can you split the difference and raise your bus voltage a little when you see a heavy load on the problematic feeders?

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: OLTC fooled by DG's

(OP)
Those three DG's haven't come in to service yet, we are in the process of the CIA. We just foresee some voltage problems may occur. One way may be considered is like what jghrist said to do a straight bus voltage regulation. Any other solutions ...?  

RE: OLTC fooled by DG's

I would consider two Load Drop Compensation controllers, arranged so that their signals summed.
With full load, and no solar contribution, The LDC on the straight feeders would call for 50% compensation. The LDC on the other feeders would call for 50% compensation. The result will be 100% compensation.
With full solar contribution and nil load on the solar feeders the LDC on the loaded feeders will cal for 50% compensation and the solar feeders will be high and the non solar feeders will be low.
You will, of course, have to juggle the percentages to satisfy site conditions.
With one bus feeding feeders with different loads, you will have to look for the best compromise.
To put it in perspective, cost wise, another option may be two buses, two LDCs, and two OLTC equipped transformers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

RE: OLTC fooled by DG's

From your description it sounds like you may be in Ontario and I've never seen a TS in Ontario that uses load drop compensatation. Mostly they only use the OLTC to maintain voltage in a specified band.

If this is the case, the solar won't cause any problems as it's a gradually changing load.

Perhaps you can confirm how the voltage is regulated on the TS?

Ian Dromey - www.dromeydesign.com

RE: OLTC fooled by DG's

(OP)
The bus tie breaker is normally closed and the two transformers secondary current is summed then fed to the LDC current input. Both transformers raise or lower taps simultaneously.  

RE: OLTC fooled by DG's

As you noted in your initial post, the LDC is designed to act for a 'load only' situation and adding generation will cause large negative flows on the affected feeders which will mess it up. I think this leaves you with two basic options:

1) Separate the feeders so that the 'normal' feeders continue to use the LDC based tap changing and the generation feeders use a different regulation scheme.
This may work but I see potential problems (i.e. you wouldn't be able to balance transformer loading) and certainly reduced flexibility.

2) Stop using the LDC control and switch to a tap control that maintains voltage in a fixed band. This is the simplest option if you can get away without the voltage boost that the LDC gives you under heavy load conditions.

So I guess the questions I would have are:
- would you have voltage problems without using the LDC?
- what voltage is the station? - if you are using 27kV or above, I'd be suprised if you had voltage problems with only 40MW load on a complete DESN station.

Ian Dromey - www.dromeydesign.com

RE: OLTC fooled by DG's

(OP)
I agree with you redfurry. The TS 2nd bus voltage is 28kV, it shouldn't but except a long run and the some laterals are small conductors.

Thanks guys for your valued comments!

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