I have been asked by a friend for an opinion...

With the new UK feed-in tariffs, a friend is considering erecting a number of small wind turbines to sell electricity back to the grid from his convenient windswept ridge. The most popular small (cheap!) wind turbines generally use an induction generator with the necessary fault protection and controls operating at 230/400V. In general such wind turbines are within a few 10's of metres of the point of supply and meter from the local power company.

In the proposed scenario, there would be 3 or 4 wind turbines, the most distant one would be 200-300 metres from the point of supply. Clearly there will be issues with voltage drop and very limited (if any) ability to clear faults if this was done at 230/400V.

An obvious solution would be to transform the voltage at the wind turbine up to (say) 3.3kV (chosen because it's a standard voltage) and transform back to 230/400V at the electricity meter. This would be a privately operated system with very limited power (a few kW) and limited fault capacity - but with a connection at low voltage to the public electricity network.

Does anyone have an idea of what the practical and legal obstacles that need to be overcome to make this scheme work, or would there be a better way of implementing the system?

Thanks

Peter

Whilst you would want to keep the alternator(s) close to the point of export, we have just witnessed the commissioning of several Gaia turbines which vary from the export point between several 10's of metres and up to 200+ metres. Each turbine has it's inverter array in a base mounted cabinet - usually the invertor provides most of the fault protection functions you need (along with G59 or G83 compliance) along with a simple MCB distribution board type protection arrangement at the export point (actually 11kV HV in this case as there was no local LV available )

The project was much like you describe - just a developer investing money to receive an equitable return to be fair

Regards

OMS

-------------------------
Failure is always an option

Did some work a few years ago at a whisky bond in Ayrshire. Very low loads and long distances. 415V supply, Switch fuse feeding a 415v/3.3kv delta star transformer, long length of 3.3kv cable then a 3.3kv/415v delta star transformer to feed the DB. worked fine, but you have to watch the low fault currents due to transformer impedance. Would the 415v fuse blow for a fault on the 3.3kv side of the transformer? or would it just burn?

Perhaps a few sums might be in order - presuming say a 15kW turbine, line fuses are around 20A - for 5 second disconnection thats about 2.9 ohms and 430Amps.

16mm2 SWA would have a resistance of around 2.9 ohms/kilometer.

Deduct say half that for source impedance and you still have a long length of cable to play with

Regards

OMS

-------------------------
Failure is always an option

Hi

Thank you for your replies. I now have some ideas of the issues and how to proceed. My big worry was fault clearance time if someone put a digger through the cable at the turbine end...

Thanks

Peter

Can Merz-price protection be applied to the cable that you are concerned about? I thought most HV systems use this form of protection.

Regards

Marty

Mertz-price protection could be used but it tends to be exspensive, all the CT's pilot cores and circuit breakers required. Few cicuits below 33KV use unit protection. Most DNO's 11KV networks are open rings with overcurrent protection at source.