MV Breaker 86BF Trip 3

[dtour]

I was hoping to get some in input on potential root causes for the activation of an 86 lock-out relay specifically used for a breaker failure feature (referred to as 86BF on the attached drawings). We took down a large portion of our facility due to the activation of this 86BF that I found to be tripped with no trip command sent from the protection relay. There was no fault, or equipment damage found. Equipment was energized again with no issues; 86BF reset just fine.

This has actually happened before on this same switchgear/breaker line-up but not on the 86BF, rather just the 86 lock-out relay that trips the local medium voltage breaker; breaker was tripped, 86 was found tripped but the protection relay did not issue a trip command.

The circuit seems pretty simple, so I'm not really sure how that 86BF lock-out relay coil could have been energized. It sits on a 125VDC system, that typically operates 130-133VDC. The indicator light is a full voltage (direct connected) LED, that was found to be working just fine after the event.

Thanks in advance.

 

[stevenal]

The light and lockout relay coil creates a voltage divider circuit. Perhaps a DC transient put you over the threshold to trip the lockout. Perhaps the pickup voltage of the coil is particularly sensitive.

 

[davidbeach]

I've seen lights short out; that would give you a path. Could something be vibrating the relay and causing the output contact to close uncommanded? I've also encountered condensation in relays causing outputs conduct without any command.

 

[dtour]

Thanks for the feedback, all possibilities.

Vibration is possible although this substation is fairly remote on the facility (fenced it). Moisture could explain the irregularity of this event.

With regards to a DC transient, that is actually the path that I originally started down, and I'm having trouble believing it due to how high the "threshold" (pick-up) voltage is listed on the LOR specifications. It's listed at around 70VDC. Right now the indicator light is basically taking the full voltage drop of the circuit across it. That said, I'll probably need to get the component (light and LOR coil) impedances and work out the voltage divider as you mentioned to help prove or disprove this theory. I'm curious how high my DC voltage would need to be in order to reach a possible threshold voltage. I read a white paper from GE that stated you can have nuisance trips at less than half of the lower operating range of your coils. Good note to keep in mind for this type of event.

 

[Mbrooke]

My best guess would be a fault in the circuit. Most substations I've designed utilize two outputs to close on the relay (negative one output, positive on the other output) in order to initiate a breaker failure trip.

 

[davidbeach]

The light should be in the k ohm range while the trip coil of the 86 would be 20 ish ohms. The coil works more on current than on voltage per se. With the light functioning normally there's not enough current to operate the coil and nearly all of the voltage is across the light. But if it shorts out...

 

[DTR2011]

I've seen similar spurious trips from LOR's, while troubleshooting a DC ground fault. By simply operating the DC breakers, to locate the circuit the GF was on, two separate Electroswitch LOR's operated. Fortunately the plant was down for the troubleshooting. I concluded it was transient voltage spikes, as it was impossible for the protection relays to operate (no load) and there were no targets, SER, etc.

When maintenance testing a 125VDC LOR (ramping up DC voltage for minimum pick up), it is not uncommon to find pick up at around 30 Volts for an ES Series 24.

 

[JensenDrive]

A way to bypass wondering if the light is the source: monitor the voltage across the BF output with another relay input, and in relay logic, use another relay output to run the light.

 

[flmadero]

What is the 86BF output configuration on protection relay?
Could you post a print screen of it?

 

[clay9_24]

In metal clad switch gear DC grounds are a nightmare. An unintentional ground from a swingdoor may appear and disappear depending on the moon. Battery grounds are never a problem when you have them but when you have two at the same time anything can happen. They are the cause of 70% of the unintentional trips that i have seen. All battery systems should have a ground fault detector on them to detect grounds and they should be monitored by SCADA or a fault recorder.

The light is built into your LOR relay from your drawings. I have seen multiple LOR relays trip due to internal circuit fail in the LOR light circuit.

 

[Sn00ze]

Are you able to post the part number for that particular LOR?