Wind Turbine and neutral connection

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gbegey

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I have been contacted by a wind turbine company to assist them in an installation for a test site. The turbine output is 480volt 3ph via inverters.
The building it will feed has a 208/120volt 3ph 4w service. We were going to put a trnsformer by the building to bring the 480 to 208/120 volts. I have since been told that they will need a neutral at the tower to measure line to neutral voltage. I asked where the neutral will be connected to and was told that we should supply a wye-wye transfomer.
1.) Since the transformer is for feeding the building, how could there be a neutral derived for the 480 volt side?
2.) If this connection is correct and the neutral is only for the ability to measure the voltage, how would the conductor be sized? The output of the turbine is 150kw.
 
I suppose you could install a zig-zag transformer at the output of the turbine to derive a neutral, but I am wondering why they are interested in line to neutral voltage. I think a full size neutral would be required in looking at NEC 220.61(C)(1).
 
Your step down transformer cannot create a neutral on the 480V side, regardless if it was a special wye-wye construction. Though as wirenut said, you could add a second zig-zag transformer to create one.

There is no need for them to measure line-neutral voltage at their tower unless they are creating it. Someone is misunderstanding a requirement.

Is the 480-208Y/120 transformer in your OP for monitoring purposes or to connect the turbine to the power grid?
 
I think the output is probably 480 WYE in which you would bond it just like a 480 volt three phase 4 wire service service, the neutral would not be used for anything other than being common to ground at the transformer and would be connected to the grounding electrodes. The transformer can be a delta-WYE with no problem.
 
The transformer is a 150 KVA to supply power to the building. It will be connected to a breaker within the distribution panel. The neutral is for "anti islanding" requirements for the inverters.
 
The inverters may be (3) 277V inverters coordinated to be 120 deg offset to create 480/277V. Maybe that's where they get the neutral and want to be able to measure at the inverter output.
 
something isn't adding up for me. If the source (tower) is 480Y/277, that neutral is coming from the source - not being derived at the transformer. So they just need a neutral connected at the source and run with their source power to controls ? Why would the transformer care if it was wye-wye or delta-wye in this case ?
 
gbegey said:
The transformer is a 150 KVA to supply power to the building. It will be connected to a breaker within the distribution panel. The neutral is for "anti islanding" requirements for the inverters.
Click to expand...

Anti-islanding is not an widely recognized electricaly term. As for clarification.

I believe you will find that the output of the inverters must be kept solidly connected to building reference. We accomplish this by bonding separately derived systems to our ground grid. It is not accomplished through a wye connected primary (unless it happens to be a utility multi-grounded neutral system typically 2400V and above).
 
Wye Connected Inverters

Wye Connected Inverters

Ron may have it right. If the output stages are inverters, using a ground reference and 277V inverters may be their design choice. A wye-wye transformer will interface properly. With a wye-wye transformer, there is no neutral to derive.
 
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