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Breaker ground settings for industrial systems

Breaker ground settings for industrial systems

Breaker ground settings for industrial systems

(OP)
What methodology is used to set the feeder breaker ground settings in industrial places?
SC calculations?
I have the phase settings for the breakers.

RE: Breaker ground settings for industrial systems

As low as practicable, but high enough to trip the breaker (if supposed to be tripped), coordinate with downstream devices with GF and avoid nuisance trips. Protection setting is as much an art as science.

Rafiq Bulsara
http://www.srengineersct.com

RE: Breaker ground settings for industrial systems

Feeder E/F relays are usually set to coordinate with the O/C and hi-set of the largest load without dedicated E/F protection. For motor starters that's usually about 50HP or so. If the MCC is designed by idiots or accountants (or EPC contractors flame ) then sometimes none of the motors have E/F protection. From an operational perspective losing the whole board because of a load circuit fault quickly becomes irritating.
  

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If we learn from our mistakes I'm getting a great education!
 

RE: Breaker ground settings for industrial systems

Scotty -I see that EPC remark.   Remember, I wasn't working for them when they built that plant!

Given that, as an EPC, we seldom put GF on 480V motors. Ground faults on any motor over about 50 HP does trip the whole MCC because it is too dangerous to set the breaker's GF protection pickup or time delay any higher.  However, we try to get the client's to go with a high resistance grounded system with a good maintenance staff (like you) so faults can be quickly located without anything tripping.

On IEC projects, we usually  include GF protection on individual motors, just not on yours.

I accept the lashes.

RE: Breaker ground settings for industrial systems

Quote:

Protection setting is as much an art as science.
Try the book "The Art and Science of Protective Relaying"

RE: Breaker ground settings for industrial systems

Hi rcwilson. smile

British code prevents use of anything other than a solidly earthed LV system except under very specific circumstances. Isolated or impedance-earthed systems are very rare over here.

I'm sure a lot of the problems in that plant had their roots in a weak spec and a construction program where doing things quickly was considered more important than doing them right, and all being masterminded by an organisation which made the mafia appear honourable and trustworthy.
soapbox
  

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If we learn from our mistakes I'm getting a great education!
 

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