Grounding a generator on a 3-wire system

[X49]

I have a facility with a 600V 3 phase service. The service transformer is delta-wye, but a neutral wire is not being connected to the service equipment (no 347V loads). We are going to be installing a standby genset and 3-pole automatic transfer switch. Can we just leave the generator neutral open and connect a bonding conductor from the genset to the main switchgear?

Thanks

 

[rbulsara]

It always helps if you mention which part of the world you are located in and what codes apply in the region.

If you are in a NEC or CEC territory(judging from your voltages and wordings), you should ground the Gen neutral at the generator. The non-current carrying metal parts parts should still be bonded together and grounded.

This is very well explained in NEC ( and I would assume also in CEC). Regardless of the codes, a source must be grounded unless you have a reason not to do it.




Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

Not quite enough info.
How is the supply system grounded? Ungrounded, corner grounded, high resistance grounded, low resistance grounded, a sophisticated grounding system? Ungrounded and corner grounded are unlikely.
If the generator grounding does not match and integrate with the transformer system grounding, you may have issues with your ground fault protection.

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

 

[X49]

The supply system is low resistance grounded, and I must follow the CEC. I am assuming that I must connect the generator neutral to the ground bus in the main switchgear or ATS with a bonding conductor. Is this correct?

 

[rbulsara]

Not necessarily. You can also resistance ground the gen neutral, if there are no L-N loads.

Also read up on grounding separately derived systems in CEC.

Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

My preferred method of generator installation is to connect the generator as if it was a load.
That is:
Connect the generator directly to the system neutral.
Ground the generator frame to the system ground, following the equipment grounding rules.
In other words connect the generator as if it was a piece of three phase equipment that required a neutral. Five wires will be required.
Yes, I know that there are special circumstances such as extra long distances from the generator and/or sophisticated protection schemes that require other connection schemes.
However a three pole transfer switch and a direct connected neutral will result in the cheapest, simplest, and most dependable installation when this basic scheme is possible.

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