Embedded generation in weak distribution networks

[topbanana]

I am attempting to carry out my honours year project (BEng) on the above subject using an actual case study of a wind farm connected to a local PES's weak section of network. The problem is that of over-voltage when the 2MVA of generation is running at full capacity under no load. The result being the network voltage may be over the UK statutory 6% allowable voltage level on occassion. The solution that is going to be implemented on a trial basis, with the intention of becoming a possible policy for similar installations is connecting a step voltage regulator to control the network voltages, being located at an optimal section up stream of the generator. The generator is being connected to an 11KV overhead line, radial distributor. I do not know enough about why the voltages are so high to allow me to analyse the problem for the start of my project, and I would very much appreciate any comments from anyone and/or any recommended reading that may enlighten me

thank you very much
Brian Thomas

 

[jbartos]

Suggestion: There may be many industry standards, regulations, safety codes, etc. and their ramifications and interpretations, which make your project more difficult. Perhaps, someone from some Architectural/Engineering firm could provide resources and hints to complete your project.

 

[electricpete]

Forgive me if I am stating the obvious.

To a good approximation, real and reactive power flow are "decoupled" in real power systems.

One consequence of this behavior is that voltage is determined primarily by the reactive power flow in MVA(relatively independent of the real power flow - MW). One possible way to bring the voltage down at a given location is to absorb vars at that location. The generator may be capable of absorbing some vars (within it's capability curve). If you happen to have any syncronous motors at the site you can adjust the excitation to make them absorb vars. If there are any power factor correction capacitors at the site you can decrease voltage by disconnecting the capacitors (var sources). You may also purchase a "shunt reactor" which is a large transformer-like device that absorbs vars. (Remote switching capability of the shunt reactor might be required.)

Switching the permanent taps of transformers in the network can change the and can affect reactive power flows. A similar affect to a step voltage regulator (the idea that you started with). In my limited experience, automatic voltage regulating transformers tend to be high-maintenance low-reliability devices (as compared to transformer which has no moving parts).

 

[jbartos]

Suggestion to the previous posting: Have you noticed that there may be solid state on load tap changers for power transformers, which do not have moving parts? This could potentially be undermining the project of this young talent.

 

[electricpete]

jbartos:

You said: "Have you noticed that there may be solid state on load tap changers for power transformers, which do not have moving parts?"
My response is: It is obvious that the technology is available to make load tapchanger without moving parts, but I have never heard of one that is commercially available. Have you? If yes why don't you come out and say so? If no, why are you making insinusations in the form of a question?

You said: "This could potentially be undermining the project of this young talent."
My response is: I've provided my opinion, which was along the lines that he should consider alternatives to his stated intention of using a step voltage regulator. I even used the qualifier "in my limited experience" to make sure it would be understood in the proper context. I don't know what else can be expected. You would do well to stick to your useful comments and avoid unnecessary criticism of others.

 

[peterb]

First off, can you define the type of generation used. My limited experience with wind turbines has been with induction generators - these do not have a field winding and require an external supply to generate power into the network. It is usual to install capacitors to improve the power factor of the generator, so as to avoid excessive reactive loading of the power system; if these capacitors are incorrectly sized, the generator could become self-exciting when isolated from the grid, and the voltage would not be controlled in this event.
If this is the case, then what electricpete suggests is the possible solution - switch the capacitors to provide a rough voltage control. Needs lots of good solid research and sounds like a great project.

If the generators are synchronous type, they will be equipped with voltage regulators that should take care of the problem when correctly set up.
You say that the generation is connected to an 11 kV radial distribution feeder. Is there load on this feeder? How does the generation get to be unloaded in this configuration? Does the feeder disconnect from the main supply, leaving the generation feeding a low feeder load?

 

[jbartos]

I beg your pardon electricpete, I was not aware that you were so sensitive. Today's power industry is changing fast, with the fast changing power electronics. Visit

http://www.inverpower.com/products/svr/svr.html

http://www.controlledpwr.com/products/700/700faq.htm##1

etc. for more information
Also, a suitable Electrical Power Analysis software might be used for the voltage drop studies, e.g.
SKM, Inc. (DAPPER, A-FAULT, etc.), OTI, Inc. (ETAP), EDSA, etc. These businesses have their websites.

http://www.skm.com

http://www.etap.com

http://www.edsa.com