parallel generators and HRG

[wirenut1980]

Every one I've seen uses a separate HRG per source, located at the source. Why would one add the complexity required for a single HRG?

carl

From the IEEE Green Book:

When total ground-fault currents with several individual impedances would exceed about 1000-4000 A, a Common Ground Point and single impedance to limit the fault current should be considered [Fig 8(b)]. The advantage of this connection is that the maximum fault current is known and selective relaying can be used to open tie breakers and selectively isolate the faulted bus.

 

[coulter]

From the IEEE Green Book:
Quote:
When total ground-fault currents with several individual impedances would exceed about 1000-4000 A, a Common Ground Point and single impedance to limit the fault current should be considered [Fig 8(b)]. The advantage of this connection is that the maximum fault current is known and selective relaying can be used to open tie breakers and selectively isolate the faulted bus.

Yes, it does say that. However, if you read three paragraphs above that:

For Impedance Grounded Systems it is always acceptable to separately connect each neutral to ground through individual impedances [Fig 7(b)]. Each impedance rating should allow sufficient current to satisfy the criteria for the grounding system being used.

And it gets rid of the need for 4pole CBs and full current neutral conductors.

Individual neutral switching devices (automatic or manual) are not recommended, since incorrect operation may allow a power source to operate ungrounded.

I'm still holding out for one per source

carl

 

[wirenut1980]

Yes, it does say that. However, if you read three paragraphs above that:


And it gets rid of the need for 4pole CBs and full current neutral conductors.


I'm still holding out for one per source

carl

I know it says that. I quoted it earlier in this thread. :grin:

I agree that I would also choose to use one per source as well. But you had asked when you would ever use a single point source and I provided a reference.:smile:

 

[coulter]

I know it says that. I quoted it earlier in this thread. ...

Yes you did, post 4. Sloppy me - I always try to give credit when someone has already opened a subject.

... But you had asked when you would ever use a single point source and I provided a reference.

You're right , the green book shows that one per system is an acceptable design. I have never seen an instance where one would want to do that.

carl

 

[wieand]

single point grounding for parallel sources

single point grounding for parallel sources

"Why switch it '. First thing I can think of is two of the sources are Utility,
and from seperate sub-stations."

The high side where the Utility connection is made is a 3ph delta (no neutral) so the separate substations do not play a part. Also the neutrals are multiply grounded along the distribution line, so the last bond for each is near the property line. And many of the distribution circuits will have a sectionalizing manual switch which will have both utility neutrals cross connected at the switch (unswitched neutral for the utility) also near the property line.

On the LV side, an insulated connection (THHN) could be made from each source to a common HRG. This is simpler to me.

Simpler than trying to install multiple CT's for GFP and switching all of the "neutrals".

Some power houses use a switching arrangement where only one of the generators are connected solidly to ground at the neutral. The switching is made to have the largest generator in operation as the one bonded and all other parallel generators un-'grounded' (at the XO)

 

[benaround]

Carl, Wirenut1980, Wieand, Laszlo,

A tip of the hat, to all of you. I learned a lot about HRG systems thru your

knowledge and experience from this thread, Thanks.