Transformers and Lockout Relay 86, can you say you don't need it?

[majesus]

Basic question on Lockout Relay 86 and power distribution transformers used as voltage step down for industrial sites. Typical transformer sizes are from 10MVA to 500kVA with LV secondary (600V or 480V distribution).

Curious to know at what transformer size do you typically not use the relay 86? I have seen Engineers use lockout relays for 5MVA XFMRS (4kV to 600V) while other Engineers do not.

Safer is always better, but sometimes, your upstream relay doesn’t have the 86.

Just like an opinion on it.
Thanks,
Majesus

 

[ScottyUK]

I'm old-fashioned and small-c conservative. I like a mechanical trip & lockout relay on any transformer feed which originates at an HV contactor or breaker. I am slowly starting to come to terms with the 86 function being integrated into a multifunction relay, and I'm still not sure I like it.


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If we learn from our mistakes I'm getting a great education!

 

[pwrtran]

It depends on what level of protection to be implemented. Lot of industrial subs only have primary fuses, no relay at all and it is okay.

 

[majesus]

Fair enough, I'm always keen to add 86 relays whenever I can, but a lot of times I am working on equipment sourced by others. Sometimes I see an 86 relay othertimes they are not included.

 

[davidbeach]

If it is protected by fuses or low voltage breakers with built-in trip unit then no lockout. If protected by breakers or circuit switchers and relays then absolutely a physical 86 relay. Software 86 function is just asking for trouble. Murphy loves the software 86.

 

[pwrtran]

We put lockout function to transformers to prevent our control room operators from doing none sense via SCADA.

On the low voltage side, it is done by putting "DO Not Operate" Tags. Again, it do not guaranty idiot thing won't happen (we had an incident that a person close one DC breaker that has a tag on)

 

[oldfieldguy]

ditto pwrtran, plus, I train operators and electricians that the operation of the "86" denotes serious stuff wrong with the transformer, such as differential operation or fault pressure relay operation, events that require more than cursory examination before attempting to re-energize.

"If the 86 is operated, notify the shift engineer or maintenance engineer and let THEM decide what the next step is."



old field guy

 

[stevenal]

Seems to be some confusion regarding the difference between a protective relay initiated 86 lockout versus lockout/tagout and SCADA disable. The question was about the former.

 

[pwrtran]

Nope. It should be clear when mention the function number 86, it is protective lock out and require a personal physically stand in front of the relay to reset after the investigation.

Tagged or Tag Out is operations lock out, same as disable the scada control, it follows the utility work protection code.

Most LV breakers protection do not have a 86 function after a trip and have to be tagged before the root cause found.

 

[majesus]

My questions was strictly about when can you justify that an 86 relay is not required on the upstream protection of an industrial XFMR with a capacity between 500kVA and 10MVA. The response is similar to what I found talking with a few local Engineers. Some have said good to have it in, other said that they have seen a lot of installations where it does not exist.

What is the procedure when an upstream breaker trips, that's a different topic.

 

[oldfieldguy]

When you deal with industrial situations and transformers in that size range, you start seeing a lot of personal opinions at play. One of my clients specified it in all transformers with secondary voltages above 2300 because this was basically where he also required differential protection.

I have seen clients who required it on transformers >2500 kVA.

There has also been discussion about using a separate reset button on microprocessor relays in lieu of a separate, physical and somewhat clunky and archaic 86, but I take a conservative approach and when an 86 is desired, I specify the old, clunky thing.

old field guy

 

[westex]

>>>>pwrtran<<<<< The utility that I work at we install 86LORs that are SCADA resetable. Mostly on Buss Diff and not on breaker failure.

 

[davidbeach]

SCADA reset defeats the whole purpose of an 86; somebody needs to go look. Can't do that from a remote control center.

 

[jghrist]

I think the question should be: At which transformer size is differential relaying an a circuit breaker justified vs fuses? If differential relaying is justified, a lockout relay would be used. Below 5 MVA, fuses might be considered to save the cost of relays, CTs, and breaker.

 

[pwrtran]

I agree with davidbeach. 86 should not be SCADA resetable. Years ago we had transformer differential and gas trip operated and someone just did not believe SCADA alarm and tried to close the breaker several times! Now we also implement bus protection trip and lock out all feeder breakers to prevent some idiot operator to close the breaker via scada causing back feed! Anything could happen, who knows. :-(

 

[westex]

With out looking at our standard prints I think the only one that is definitely not resettable via SCADA is the breaker failure 86. I guess my company's thinking is buss biff could have been lighting or something on the buss that is now clear. We use 86s on the buss dif as a contact multiplayer also. Beside if you have a buss diff condition the fault (if still there) would be contained inside the fence. Also the 86 for UFLS and our 86s for O/C is resettable via SCADA. But as far as transformer diff your right, I dont think we install resetable.