grounding

[tulum]

Hello All,

We have a new system that is fed from a single D-Y transformer. We are now adding an alternate source (a generator). We would like to resitance ground both sources.

The questions is can this be done with one NGR? The suggestion was made to place a zigzag with NGR in the secondary lineup so that we only need one NGR for both sources....does a zigzag work fine on a the secondary of a wye transformer?

 

[rbulsara]

Hire someone who knows grounding!

Rafiq Bulsara

http://www.srengineersct.com

 

[tulum]

It was a simple enough question. I did not ever say that I was designing the system. Sorry for trying to learn a little something along the way. If anyone else feels that they have something to actually contribute it would be appreciated. Else - please keep your comments to your self, this is a chat forum that is typically - used to chat / learn.

 

[waross]

Well, the question did not show much understanding of electrical systems but I have seen worse done by EEs.
The zig-zag is the joker. It is used one of several methods used to generate or develop a neutral point for grounding when one does not exist. Artificial neutrals are superfluous when a true neutral such as a wye point exists.
This brings us back to Rafiq's suggestion, hire someone who knows grounding.
As for a single NGR, not enough information to say. It depends.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[EEIre]

Subject is more complex than it seems. Recommend reading IEEE Orange Book: Std 446 IEEE Recommended Practice for Emergency and Standby Power Systems for Industrial and
Commercial Applications

 

[waross]

What are your voltages and loads, Tulum?
What is the KVA rating of the generator?
Is the generator wye or delta?

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[JoseAngelTec]

thats a really good question! whats an NGR anyways all i can say is make sure youre loads are well ballanced and xo on secondary from trans well grounded and confirm that the conection on the generator is wye and well grounded too and make sure the voltages are the same make sure you ground bolth Y's on the trans and the gen an eng i work with burned a bunch of lamps once testing a gen that did not have the Y grounded !

 

[mmt019]

If your existing system has no 4-wire loads, then it might be possible to make it a high resistance ground system. If there are 4-wire loads, then an HRG system is not possible. Are both the utility main and the generator main in the same switchgear lineup? Is so, is it set up as a single point ground or a main bonding jumper for each disconnect? Is the transformer neutral grounded at the transformer or at the switchgear OR both places? Is it a low voltage, 480V system? You can purchase a stand-alone HRG detection system with the pulse option (for finding the fault) and locate where you can disconnect the neutral from the transformer and run a #8 AWG (generally speaking). Forget the zig-zag configuration. The zig-zag is for a delta system. Goto this website, that should get you thinking:

http://www.postglover.com/pulserplusnet.html