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pranandclt
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Join Date: Sep 2010
Location: Hubli ,Karnataka,India
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VCB Tripping

05/15/2011 2:35 PM

The VCB in my firm is tripping at full load due to earth fault. This happens at full load after 5 minutes or so.Could any one throw some light on this issue

Thanks in advance.
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TonyS
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#1

Re: VCB tripping

05/15/2011 4:38 PM

I can lend you a torch!

You need to give more information.

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NUKALA
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#2

Re: VCB Tripping

05/15/2011 11:54 PM

Can you give me the info related to make of VCB.
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kvsridhar
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#3

Re: VCB Tripping

05/16/2011 12:21 AM

Since it happens after 5 minutes of full-load running, some thermal phenomenon is indicated....to wit, some conductor's insulation is developing a leakage to earth, after getting heated a bit. You can perhaps trace that weak point by meggering.

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ramvinod
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#4

Re: VCB Tripping

05/16/2011 4:27 AM

Please furnish the following information to help you. Relay make and type. CT ratio. Relay settings. Load current. What was the current when VCB tripped

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manindra
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#5

Re: VCB Tripping

05/16/2011 6:48 AM

What's the rating of the VCB? The Earth fault relay is residually connected? If so, in full load condition, if there is substantially amount of unbalance current, zero sequence component of unbalance current may flow thru the earth fault relay and may cause tripping.

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kvsridhar
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#7
In reply to #5

Re: VCB Tripping

05/16/2011 9:13 AM

Dear manindra,

i have a small doubt here. In all systems i have seen in LV, all four cables (3P+N) pass through the core-balance CT (CBCT) which vectorially sums up all the currents, including any unbalance currents. The relay will not trip for any unbalance, only for any current flowing outside the CBCT, which can only be an earth leakage/fault. What you are saying here is different...maybe things are different in MV/HV ? Not that i think so....

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manindra
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#8
In reply to #7

Re: VCB Tripping

05/16/2011 9:34 AM

Dear kvsridhar,

What you have told in case of CBCT is absolutely true. I have indicated that in case of Earth fault relay is residually connected in the CT secondary circuits, in case of high line unbalance currents, zero sequence component of unbalance current may flow thru E/F element and if that amount exceeds threshold value(pick-up value) E/F relay may operate.

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kvsridhar
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#9
In reply to #8

Re: VCB Tripping

05/16/2011 9:43 AM

Ah, ok. i think i get it. Thanks.

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hien.nguyenquoc
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#10
In reply to #5

Re: VCB Tripping

05/16/2011 9:50 PM

Additional to manindra:

1. What is the parameter shown at the point where the trip occurs?

2. What is the setting range?

3. What is the type of earthing protection scheme?

4. What is full load current?

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PWSlack
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#6

Re: VCB Tripping

05/16/2011 8:51 AM

What's so difficult about eliminating the earth fault that is causing the trip?

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