Mains tripping

[jim dungar]

No arguments here with anything posted in response to my described approach.
... except I disagree that gf settings will affect arc flash PPE requirements. Granted they could minimize the incident energy for an Arc Flash, and minimize damage as well.
I suppose I'm driven by reliability and uptime, while still meeting code requirements. That's an easy philosophy to defend to a Data Center manager.
However, I do see merit to a lesser GF adjustment in some cases, so I appreciate the alternative point of view, and will consider it where possible.

To Jim D I pose the question: On a 35kV, 600A circuit, where do you set your ground-fault pickup?

John M

Ground fault settings do not directly impact arc flash. My comment was meant to show that I keep my branch circuit devices as low as I can which then allows me to keep my GF settings lower than maximum.

On 35kV, there are too many items to consider to answer such a vague question. A single relay protecting an underground campus network of fusible switches would probably be handled differently than an open air substation containing 5 station breakers.

 

[mayanees]

No

No

You responded: On 35kV, there are too many items to consider to answer such a vague question.
I say: Not vague at all.
How do you set it for the two situations you proposed?
John M

 

[mayanees]

Okay, I'll go first....

35kV, 600A MCB, Metal enclosed sheltered-aisle switchgear:
51N MCB LTPU setting of 20% of 600 or 120 amps;
51N Dist CB LTPU settings of 60 amps.

These settings were developed with concurrence from some experienced Power Engineers, but the magnitude selection seemed somewhat arbitrary.

I'm curious about other folks' experience with ground trip settings on this type of equipment.

John M