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Topic Title: Grounding 600V 3 phase generator
Topic Summary: Ground or not to ground ?
Created On: 27 September 2013 05:45 AM
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 27 September 2013 05:45 AM
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Pat Lucey

Posts: 29
Joined: 18 May 2006

You have a 3 phase 600V standby generator. The generator windings are Star connected for 600V output. This unit will feed directly to a 600V delta / 208V / 120V Star transformer which then feeds a mix of three and single phase loads. ( Proper fusing and disconnects will be fitted. )

Do you :-
1. Fit no grounding wire from the generator star point to ground.
2. Fit a solid ground cable from the star point to the machine frame.
3. Use a Resistive ground on the star point.

Thanks.
 27 September 2013 08:07 PM
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OldSparky

Posts: 580
Joined: 28 June 2011

me i would ground the machine frame, but others might have different ideas..

what is it feeding? motors, ?
 30 September 2013 06:10 PM
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MickeyB

Posts: 181
Joined: 18 January 2003

The downstream 600/208/120V Tx is acting as a separately derived TN system which can be derived from an upstream TN (earthed neutral) generator system. This is pretty common for connecting downstream UPS/ PDU's with an isolating transformer or any other load which is separately derived. At low voltage the NE of the downstream transformer should be connected to a reference earth. The Tx is 3 phase 3 wire with a 4 wire output.

In reference to your questions:-


1. Fit no grounding wire from the generator star point to ground.
No, ground the generator as per normal. Ground/ Earth frame and take Neutral point out to NE reference.

2. Fit a solid ground cable from the star point to the machine frame.
Neutral/ Earth/ Ground point either at switchboard/panelboard or at generator earth nest/pit/ UFER etc.. UK preference is for panelboard to keep it simple and safely out of the way...

3. Use a Resistive ground on the star point.
Should be no need at this voltage unless the fault current could damage the insulation on the windings of the machine.....
Ask the manufacturer of the alternator whether solid grounding/ earthing is acceptable.
It's all about the fault current and the thermal withstand of the machine windings. There will be a 'damage curve' for thermal damage of the windings......


 01 October 2013 07:59 PM
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OldSparky

Posts: 580
Joined: 28 June 2011

Originally posted by: MickeyB

The downstream 600/208/120V Tx is acting as a separately derived TN system which can be derived from an upstream TN (earthed neutral) generator system. This is pretty common for connecting downstream UPS/ PDU's with an isolating transformer or any other load which is separately derived. At low voltage the NE of the downstream transformer should be connected to a reference earth. The Tx is 3 phase 3 wire with a 4 wire output.



In reference to your questions:-





1. Fit no grounding wire from the generator star point to ground.

No, ground the generator as per normal. Ground/ Earth frame and take Neutral point out to NE reference.



2. Fit a solid ground cable from the star point to the machine frame.

Neutral/ Earth/ Ground point either at switchboard/panelboard or at generator earth nest/pit/ UFER etc.. UK preference is for panelboard to keep it simple and safely out of the way...



3. Use a Resistive ground on the star point.

Should be no need at this voltage unless the fault current could damage the insulation on the windings of the machine.....

Ask the manufacturer of the alternator whether solid grounding/ earthing is acceptable.

It's all about the fault current and the thermal withstand of the machine windings. There will be a 'damage curve' for thermal damage of the windings......







wow :0 what does that mean?
 08 October 2013 04:53 PM
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MickeyB

Posts: 181
Joined: 18 January 2003

A bit of mix and match of US and UK terminology.... basically earth the neutral as you would normally.
 08 November 2013 01:49 AM
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Pat Lucey

Posts: 29
Joined: 18 May 2006

Thanks for your replies.
We did ground the neutral ( star point ) of the generator Some people said this was not required as the generator ONLY feeds the primary of the Delta / Wye distrubution transformer. ( 600V primary / 240-120V secondary ).

Cheers pat.
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