Lockout Relay 1

[timm33333]

I am wondering why sometimes a separate relay is used for 86-lockout, whereas 86-lockout can be integrated into other relays (for example in GE F35 relay), thanks for help...

 

[davidbeach]

You'll probably find it to be a Mac vs. PC type of thing. Relay manufacturers want to make you think that the relay can provide a lockout function but everybody in the field knows that a real lockout is the only way to go. I'll use relays for all sorts of functions that used to require some form of aux relay, but we'll always have lockout relays and control switches. Everybody that goes in the station knows what those are and they're pretty much the same everywhere while we have all sorts of relays.

 

[oldfieldguy]

I have facilities where operators have had to deal with several generations of protective devices. Operators being relatively simple-minded folk, I teach the cardinal rule: You don't reset and re-energize after the lockout rolls. Call your electrician.

In other words, I employ them as a measure of fault classification.

In pre-microprocessor relay days, the lockout relay was also a common 'contact multiplier' so that one protective device could trip several breakers.

Further, it was typically employed to block reclosure on serious faults, ostensibly to make sure that a thorough investigation took place before throwing power back into faulted equipment.

Yes, you can program microprocessor relays to require manual reset, but in my admittedly archaic mind, nothing says 'NO!' quite like a rolled lockout relay.

old field guy

 

[timm33333]

So if we have 3 relays (overcurrent, undervoltage, overvoltage) to trip one breaker, can we put one microprocessor lockout relay just before the breaker: this lockout relay will have three inputs from 3 relays (overcurrent, undervoltage, overvoltage) and 1 output (the output is the trip signal to breaker). will it be Ok?

 

[ScottyUK]

Why would you want a [μ]P-based lockout? Dumb = simple = reliable. No electronics!

 

[davidbeach]

The possible existence of microprocessor lockout relays will be firmly denied by all the field personnel I know. A lockout is an electromechanical device that thunks into the tripped position and stays that way until manually twisted back into the reset position. A microprocessor lockout is a perfect example of just because something is possible doesn't mean it needs to happen or even that it should happen.

On the other hand, all those protective functions you listed should be implemented in a single microprocessor relay and duplicated in its redundant companion.

 

[timm33333]

Sorry what does 'duplicated redundant companion' mean? Does it mean back up relaying? Is back up relaying used in industrial plants?

 

[DTR2011]

"duplicated redundant companion" = back up relay for microprocessor protection. Even if the relay never fails, unless you either want to take the line out of service or perform testing & maintenance without protection enabled (not recommended) this is why back up is suggested. Don't forget about test switches for current / voltage and trip I/O isolation. Specifically on the GE F35, the terminals are difficult to get at for wiring in test signals. The additional cost of the test switches will easily be covered if you ever have testing done in the future and wires need to be lifted and the protection scheme recommissioned. You can also map each protective function through its own switch and parallel them together down stream of the test switch. If, for example you had an issue with a VT, knew what it was an needed to get the line back in service without 27/59 protection, you could open the test switches associated with these functions. Most manufacturers of FT Type test switches have a provision built into the cover so switches can be opened and the cover closed.

You could theoretically have 27/59 & 50/51 all mapped to the same output contact on the microprocessor protection and have it trip an electromechanical 86 device.

Depending on what you are protecting, 27/59 may not suggest serious faults and as such may not need the 'block close' (normally closed contacts of lock out in the breaker close circuit). Remember that a traditional lock out relay has (2) sets of contacts, the normally open, which trip several devices when the 86 operates and normally closed, which open up when the 86 operates and blocks the close. I have seen devices that trip only (and look nearly identical to West/GE/Electroswitch) and are generally referred to as a 94 device (Aux relay)

Although the GE F35 does have a big configurable display and many programmable push buttons available, which could make for an intelligent lockout scheme without a separate lock out device, the rolled lockout does have the history of being a device that means something serious has occurred and requires further investigation.

 

[davidbeach]

Most manufacturers of FT Type test switches have a provision built into the cover so switches can be opened and the cover closed.

Unfortunately, I think you're correct. But again, just because something is possible doesn't mean it should be done. We have a few of those, and at least they're all clear (unlike the normal covers that are all black). Normal cover that won't go on over an open switch can be placed on the screws concave side out over the open switches. Never hide an off nominal condition under a closed cover.

I'm aware that redundant relaying has ceased to be the normal condition in industrial installations and that's a matter of being penny wise and pound foolish. Back when it was one relay per phase plus a ground relay you could almost always count on two relays seeing any fault so that one failure wouldn't result in a fail to trip.

 

[cranky108]

We always install electromechinical lockouts so that a live person must drive to the site, and hopefuly look at the yard, before they reset the lockout.

There is now and again pressure from operators to make these remotley resetable, and we can make an excuse of cost, or outage time. But the answer is always we can't without consiterable work.

 

[Hoxton]

No doubt there is a written history of this somewhere.

Remembering that this comes from "old fashioned" electromechanical relay practice.

I think that the use of what we call in the UK a Master Trip Relay comes from the fact that most protection relays are self reset. So after the fault has cleared, the relays reset and remove the trip signal.

In order to lock out the system, a separate 86 relay is used, which stays in the trip position after the breaker has tripped, isolating the fault.

So there is clear and simple logic after a fault:
Go to site
Acess the HV switch room (Authorised Person in Uk)
Investigate fault
Reset 86
Close breaker

As davidbeach said, all sites are the same and the devices even from different manufacturers are much the same.

Also, during commissioning and testing, the system can be tested and each device trips the master trip relay, but not the breaker. Then one device is selected to trip the 86 and the breaker AND the plant it feeds - eg a steam turbine.

The use of the 86 system in LV plant was not used for reasons of cost not logic.

PLC systems have their place, but you have to consider the benefits of the above old fashioned system, when Plc systems have hidden logic and can be susceptible to uncontrolled modification (design drift I call it)