Single Phase Wind Generator & 3 phase connection

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024engineer

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A customer installs a single phase 20 kW wind generator (240V) but wants to connect it to a 3 phase (120/208V) service. Can this be done and if so what equipment would it take? Can the voltage be stepped down to 208 L-G and connected to one leg of the 3 phase service?
 
A motor generator or a static inverter would be able to match the wind generator's output with the service. I think the single phase step-down transformer could be a solution, but it would create an imbalance, and I don't know how best to deal with that. Why did the customer buy a single phase generator, and why does he want to connect it to the service?
 
I know there are lots of rotary phase converters bu I doubt if there are 20kW units. The biggest ever that I have laid my hands on was a 16kW unit, and it was costs a lot for the owner then. Can you do it with a rectifier-inverter setup?. Single phase generator output rectified to DC and the DC gets inverted into 3-phase AC (can be done using a VFD with a slightly larger rating than the genny; some need slight tweaking to let the VFD know it will be looking for two lines instead of the usual three lines at the inputs and some makers provide separate terminals for single-phase input operations).
 
Does the customer want to push power back on the POCO grid? There are usually restrictions on the size of size-phase units they will allow. Our cutoff is usually 10 kW unless an exception is made. Bigger than that, it usually must be a three-phase unit if the customer has a three-phase service.

Interfere with the power quality on the POCO system too much and you will get a "cease and desist" so to speak, so it is also important to check with the POCO to ensure the unit will not interfere with the neighbors. In some cases, you might have to pay for a service upgrade to reduce your impact. There may even be some cases where it just won't work.

Keep in mind that you can't always do what you want because there are conditions to being tied to the POCO system. That said, I can't imagine a 20 kW unit would be a problem in most locations.
 
If the single phase generator is connected to the 208 V line to line part of the 120/208 circuit then yes it can work. But the generator will have to match the 208 to supply power to the 120/208 V system. The utility will supply the different currents to balance the load flow to their customers. If the 120/208 V cannot take all the current produced from the generator, then the difference ends up in the high voltage side.
 
TaraPersaud said:
If the single phase generator is connected to the 208 V line to line part of the 120/208 circuit then yes it can work.
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No, because the generator's output is 120/240v 1ph, and the service is 208Y/120v 3ph. There's more than just a voltage difference to contend with.
 
Here in the UK grid connected household sized wind turbines are not connected directly to the utility supply.
The voltage and frequency of the wind turbine output would vary continually according to the wind speed.
Connection to the grid is via a grid tie inverter, similar to those used for grid tied PV. The output from the alternator is normally 3 phase 3 wire AC of variable frequency, this is rectified to DC and then inverted to match the available utility supply.
Since both 208 volts and 240 volts are popular in the USA, I would expect that the grid tie inverter would be configurable for either voltage, as is usuall for PV grid tie inverters.
If the inverter is 240 volt only, then it should be fine with a suitable transformer, it wont "know" the difference between 240 volts direct from the utility, or 240 volts obtained by transformation from 208.

If no inverter is supplied, then the wind turbine may be intended for direct electric heating or for battery charging, and not for grid tied use.

If the inverter is 240 volt only, double check that is not a UK spec. one with a 50 cycle output.

You will of course need permission from the utility, and a suitable tarrif.
 
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