Leakage capacitance - Over voltage ungrounded 480VAC systems

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MrJLH

Senior Member
Location
CO
Looking for some information on leakage capacitance on ungrounded 480VAC systems. Any one know of any good resources, books, or white papers?

Any advise on when this becomes an issue on 480VAC systems? i.e. how long the circuit is?

At what point are over voltages seen?

Just trying to broaden my knowledge here.

Thanks
 

gar

Senior Member
Location
Ann Arbor, Michigan
Occupation
EE
190104-1040 EST

MrJLH:

I would call it shunt rather than leakage.

My guess is not below 10 pfd per foot and not above 1000 pfd per foot. If I remember correctly Romex is about 15 pfd per foot and the wires are close with substantial dielectric constant above 1.

Go do some measurements.

.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I can't give you any sort of solid numbers, since its been years since I looked at this. However do a search for 'restriking fault ungrounded delta' or 'transient overvoltage ungrounded delta' and that will get you pointed in the right direction.

A normally functioning ungrounded system doesn't show overvoltage, and a solidly faulted system gives a fixed line to ground voltage. But if you have an intermittent fault to ground that can 'charge' the system capacitance up. This doesn't create line-line overvoltage, since the line-line voltage is set by the transformer secondary. But the line-ground voltage can get 'pumped' to well above the normal line-line voltage.

-Jon
 
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