delta system

[platerdave]

we have a 240v delta system 3 wire how do you get a neutral
we have it to ground been fine for years a least 18. now we have unbalaced power to ground it is 147 195 94 volts changed the grounds didnt help penelec don't even no way

 

[Skogsgurra]

I have some difficulty understanding what you are saying. Do you have an ungrounded 240 V system with delta connection? And now you measure those voltages from the phases to ground?

It doesn't seem to be a problem to me. No severe unbalance - you have to expect anything between almost zero and full line/line voltage in such a system.

Is your question how to ground it? If that is the case then you obviously cannot ground the transformer center point to get a 240/138 V system. But - if your country's code permits - you can ground one of the phases and get a grounded delta with 0, 240, 240 V from line to ground. It is being done in the US and it really doesn't change much. Only that a ground fault in one of the hot phases will trip the corresponding fuse, which could be good.

I think that more and clearer information is needed before anyone can give advice here.

 

[alehman]

A delta system has no neutral. There are several ways to get a neutral. If you need three phase, you can install a delta-wye transformer. This will give you a 3-phase 4-wire system as output and you can select whatever secondary voltage you want.

Another option if you need a small amount of 120/240 volt single-phase power may be to have the utility convert the service to a 240 volt "high leg" system where a center tap of one of the three transformers (or transformer windings) is grounded. This effectively adds a 120/240 single phase connection using two of the three 240V phases and the added 'neutral'.

Theoretically you can ground one phase of the existing 3-wire system, converting it to what is called a 'corner grounded' system, but that doesn't give you any other voltages to use.

 

[mc5w]

I have also used a balance coil to convert a 3-wire dry transformer secondary to 120/240 volts 4-wire delta. This is a single phase version of a zig-zag set that is used to convert a 3-wire delta system into 4-wire wye.

Send me email mc5w at earthlink dot net if you want details as to how to protect a balance coil or zig-zag set against overloads and internal faults. Ordinary circuit breakers or fuses will not work.

Mike Cole

 

[whinton]

With ungrounded delta power systems we have added Phaseback to our power system and our phase voltages are now balanced to ground and our overvoltage problems stopped. The link is:

http://www.applied-energy.us

I hope this helps
Bill

 

[mc5w]

By the way, Penelec is in the U.S. and is a part of First Energy. They cover both upstate PA and NY along the PA-NY border. They also cover part of central PA. I am not sure of what their name is in upstate New York, but I do know that their transmission and subtransmission lines do serve loads in upstate New York.