Cable Capacitance

[electrageek]

I am working on a new wind farm project. The first string of fifteen 1.5MW wind turbines are coming online and I have a question about capacitance in the 34.5Kv distribution system. We have fifteen 1750KVA padmount transformers, one for each Wind Turbine. The transformers are all connected together on the high voltage side at 34.5Kv. As soon as we turn on the 34.5Kv voltage to the string we get approximately 900Kvars flowing out to the Utility. Is there any way to help minimize the capacitance during the construction of the system? The system is direct burial with indivdual 34.5Kv cables jumpered from transformer to transformer covering approx 2 miles.

 

[Skogsgurra]

You need switches. Nothing can be done to the cable capacitance once the cables have been installed and connected.

Are the 900 kvars difficult to handle? They are within the envelope of a single turbine/generator/transformer.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[burnt2x]

Agree with Gunnar. Automatic Power Factor Correction Cap Banks of the 900kVAR size can be helpful. You can have it in 12-step switching (75 kVAR per step switch) and set to operate at your desired PF window.

 

[Skogsgurra]

Burnt, do you mean reactor (inductor)banks? That's unusual - but could be a solution. Capacitor banks won't work, for obvious reasons.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[electrageek]

Hi Skogsgurra,

The primary substation is not complete so we are trying to use a local distribution feeder 13.2Kv to test the operation of the Wind Turbines. We have a temporary mobile substation 13.2Kv to 34.5Kv in place but are limited to 50A of total current by the Utility. When we connect to the grid the amps imediately go to approx 40A which uses up most of the av available capacity the Utility has given use. We can only run the Wind Turbine at less then 500Kw or we trip the breaker on the mobile substation. If we build more Power Plants I was trying to find a way to reduce the capacitance of the cable system. Or find a company that build inductors to cancel the capacitance for testing at this site.

 

[Skogsgurra]

I think that any transformer maker could build you the inductors needed. I didn't even think of that possibility. If you are lucky, there could even be some to rent.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[KJLRSA]

Depending on your location there are numerous reactor manufacturers around.

Namely: Nokian - Finland
BPEG - China
Sunten - Korea
Hilkar - Spain
Mangoldt - Germany
Trench - Brazil+Europe

Unfortunately I do not use the American market, and therefore do not know of anyone there.

Go to each website and they will let you know the info required from you to quote.

Allow about 12-16 weeks for manufacture and delivery.

 

[model70man]

The company that I work for builds oil-filled shunt reactors, both 3-phase and single phase pad mount dead front style up to 34.5 kV. We are in the US, east of the Mississippi. I have sold a lot of these in the western states and Alaska.

 

[PHovnanian]

This sounds like plain old bad luck as far as not having the utility facilities in place. Hopefully, this won't be the case in other installations, so buying a reactor (or other p.f. correction equipment) won't be worth the investment. Rental might be the way to go, but...

When you crank up one of these generators, what sort of kVAR demand are you expecting? The kVAR demand of an underexcited generator should offset the cable capacitance. Can you tweak that parameter? Whatever the case, the utility hasn't given you enough capacity to run even a single machine up to its rating.

 

[Kiribanda]

electrageek,

I am not very much familiar with AVR operation of the wind turbine generators (WTG).

1)Could you please post the Capability curve of WTG?

2)What is your existing mode of operation of the AVR unit of WTG?

3)Is it on AVR or pf mode?

4)Is there any provision that you can switch the AVR function to PF mode? (This will help the utility to provide reactive power requirement for the 34.5 kV cable run and not by the WTG)

Does it make some sense?





But if we look at from paralleling point of view, is there any provision

 

[electrageek]

PHovnanian & Kiribanba,

Thank you for the information. We have solved the problem, for this site, by doing just what you recommend which is to bring the Turbine Generators online underexcited to help offset the capacitance of the cable system. First we tried using PF control but it took too long to get enough Kvars to help so we were able to adjust the Voltage Regulator to get -400Kvars imediately. We also balanced the loads on the Utility side which helped a little. We can actually get to full load on one unit this way. We haven't gotten the largest cable string online yet but it looks like we have enough Kvar control to make it work. Thanks to everyone for the help.