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question on wave for capture to determine a down stream fault
2

question on wave for capture to determine a down stream fault

question on wave for capture to determine a down stream fault

(OP)
Been riddling over if a meter with wave form capture would provide enough information to sort out a down stream phase or ground fault.

The system voltage is 13.2kV with a main breaker fitted with an SEL protective relay with phase and ground fault. The 12 feeders are Westinghouse WLI fused load break switches. Each MVS has a Westinghouse DB4b-2fm 2 element watt meter mounted on the door. There are 2 CT's and 2 PT's in the MVS for the meter.

There was a ground fault on one of the feeder circuits that tripped the main breaker but we had no way to know which of the 12 feeders experienced the ground fault other than check each of the 12 feeders before being able to restore service.

Since we are planning to replace the old meters with new communicating meter would a meter with wave form capture allow us to get some idea of which feeder circuit experienced a phase or ground fault with only 2 CT's and 2 PT's?

I am thinking that by studying the voltage and current wave forms on each feeder after a main breaker trip should provide some evidence, maybe not conclusive, to narrow down the faulted feeder.

We are attempting to not have to take a shut down to add a third CT to each feeder and utilize the information we can get from a new meter.

Thanks in advance for humoring an old guy trying to figure out new technology.
Dan
A dream is just a dream. A goal is a dream with a plan and a deadline.

RE: question on wave for capture to determine a down stream fault

You would need to have three CTs to detect all Ø-grd faults. I don't know if the waveform capture on a meter can be triggered by fault current. It might be better to get an overcurrent relay with oscillography.

Better yet, coordinate the fuses with the main breaker relay so that a fuse blows instead of tripping the main breaker. This means not having sensitive ground fault protection on the main.

Is the ground fault current greater than the maximum load current? If so, you might be able to use fault indicators on the feeders.

RE: question on wave for capture to determine a down stream fault

To avoid shutdowns, it might be an option to fit earth fault indicators driven from a core balance CT fitted around each of the outgoing cables. The core balance CT can be easily retrofitted if you get a split core type, but important consideration would need to be given to how the cable screens are earthed. For example, if its an old paper insulated lead sheathed cable into a bitumen filled cable box then it would probably be too much hassle as you would need to install an insulated gland. Another option if it's an air insulated cable termination is to fit a small slipover CT over each phase of the cable inside the cable box but below the termination, ie just above the gland plate, and summate them to drive an earth fault indicator. This would need outages.

Regards
Marmite

RE: question on wave for capture to determine a down stream fault

(OP)
Thanks for the input. I failed to say that this is an industial indoor application.
If we took outages on each feeder I would add a bar CF on B phase and have 3 CT's then use a cummincating protective relay for metering and down stream fault detection and anunnciation.

I now realize that there would be no way for the meter to know when to triger the high speed wave form capture.

RE: question on wave for capture to determine a down stream fault

I can think of at least three meters that would do what you want. You will want that 3rd CT.

SEL 734/735

Novatech/Bitronics 70 series will fit into the existing meter hole, as it uses a detachable display.

The Schneider/PML ION7550/ION7650

Another option would be fault indicators. SEL makes an extensive line of these. https://www.selinc.com/FCI/Underground/

RE: question on wave for capture to determine a down stream fault

I'd be looking at the subnet unit from http://www.emsni.com/

You'd need to add a CT and PT for each phase. The advantage of this style of metering is that there is no proprietary software, so your not stuck paying annual license fees. The output of the unit can be read with as a commtrade file and takes about all of half an hour to learn to use it.

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