Digital Lockout Relay? 1

[ThePunisher]

I apologize if I am a little bit outdated but one of our client's suggested us to use a digital lockout relay.

I used to specify electromechanical lockout relays (i.e. Electroswitch, GE HEA etc.).

I never encountered a "digital" lockout relay as a separate device. At first, I was thinking an 86 function logic programmed in a multifunction digital protection relay. If one exists as a discrete digital relay, I'll be happy to be informed.

Thanks..

 

[jghrist]

I haven't seen anything expressly marketed as a digital lockout relay. It might be overkill, but you could use a programmable controller such as an SEL-2411 or SEL-2440 that list for under $1,000. I don't know if you can get output contacts suitable for directly tripping breakers.

 

[davidbeach]

There are some aspects of protection where the conversion from electro-mechanical to digital has been a great boon. There are other things, like lock-out relays, where there is absolutely no benefit to be derived from changing. Good solid mechanical contacts have many advantages.

 

[ThePunisher]

Thank you for the prompt responses. I actually require 2 lockout relays in our design. One to block bus transfer and the other to allow bus transfer. If I were to program these relays elements as part of a digital protection relay logic, I may not be able to get the number of output contacts.

Yes, the current rating/reliability of the output contacts directly tripping the breaker trip coil may also be an issue.

Are there any technical papers that relates to this? I appreciate if you can share one.

Many thanks.

 

[dpc]

Lockout relays generally provide two functions:

Large number of dry contacts with relatively high current ratings that can be used for breaker tripping, control, etc.

Hand-reset function to prevent remote operation after the relay has tripped.

Electrically-reset LOR are available, but not often used.

Your application doesn't sound like a typical use a LOR. They are generally used for tripping a lot of equipment after something bad happens.

David Castor

http://www.cvoes.com

 

[cranky108]

A digital lockout sounds like a latch function in a relay. It should be eazy to figgure out, or do. The best application for this is to prevent reclosing.

However, an electromechinical lockout is intented to not only increase the number of contacts, but is also intended to make people think before they reset them.
We always felt it was a good idea to make someone go to the site, and hopefully look at what could have caused the lockout to operate.

However we have used electrinic reset lockouts for 81 functions where the dispatcher should have control.

 

[oldfieldguy]

Dittoes to cranky108's comment.

In the industrial venues in which I work, I train operators that if the lockout device is rolled then they are NOT to reset and retry, the difference being that between a rewind of a motor or transformer, and a catastrophic failure and total replacement.

The electricians know that there are specific steps that must be taken to determine and isolate the cause of the operation.

old field guy

 

[slavag]

Hi.
What cranky108 saied.
Digital LOR, it the LATCH function in the digital relays.
In the newer digital relays possible two options:
LATCH of contact or protection function with same push button RESET or deenergizing of relay and
classical LOR with hand reset only, into digital relay

Best Regards.
Slava

 

[oldfieldguy]

Slava-

Yes, i had a discussion with some of our design folk about using latched outputs of digital relays in place of an actual and discrete electromechanical lockout relay.

I stood my ground FOR the old hand-reset, big ol' knob, separate from the reset button on the digital device because I wanted to make sure that the person responding to the trip had a substantial indication that THIS was more serious event and required more attention that "push the 'reset' button and let's try it again."

old field guy

 

[davidbeach]

Good for you ofg. A rolled lockout means something. Sometimes the protection engineer can look at the relay event reports and say "Oh, never mind" but generally a rolled lockout indicates real trouble. When it does indicate teal trouble, then there needs to be a bunch of people onside doing a bunch of testing before the lockout is reset. I'd never go with a remotely resettable lockout or a digital lockout. The whole point of a lockout is to make somebody go take a look. Why short circuit the process?

 

[slavag]

Hi.
OFG, David, I agree with your reasons, its right.
But, its a rules of operation personal.
We stop design/used LORs before a 10 ( or more ) years.
Only special request for transfromer or generator bays, from time to time for capacitor banks.
And... I prefered somthing chepaer and small sized then Electroswitch LOR .
Some bistable relay, for example.


Best Regards.
Slava

 

[oldfieldguy]

Slava-

We both don't like Electroswitch LOR for diametrically opposite reasons. I like the open contacts of the older designs.

But then, I'm pretty much a dinosaur among power people as the days pass...


old field guy

 

[cranky108]

I never liked the open contact design. They hang up, get dirty, or get wires pushed into the contacts.
Have I mentioned that they need to be torqued correctly every few years.

After some thinking, I have used an electronic lockout for a capacitor bank unbalance. Not as big a deal as an over current operation.

 

[dpc]

ofg,

Just an aside regarding Electroswitch Series 24 lockout relays - I have used these for over 35 years and never heard of or experienced any failures. I have seen failures in the GE and Westinghouse designs - although not often. The old electric reset HEA relays were definitely problematic.

One advantage of the Electroswitch design is the smaller depth for the same number of contacts.

I'd be interested in knowing what sort of problems you've experienced.

Dave

David Castor

http://www.cvoes.com

 

[cranky108]

On a series 24 I've seen a broken retainer ring (for lack of a better description), after a linemen used a cheater bar to trip the lockout. He went on to explain the lockout would not turn from the reset position, so he employed the cheeter bar.

I also have seen that when non-inusulated lugs were used, they can become bent into the next terminal.

However I've seen more problems with the GE lockouts (the old ones, the new ones look like the Electroswitch lockouts).

 

[rcw retired EE]

The Electroswitch Series 24's are easier to take apart and put back together than the old Westinghouse or the GE SB-1's with springs that went everywhere. I definitely don't recommend dismantling any of them. Design it correct the first time and don't take them apart.

I agree with David and OFG - lockouts should not be used for "recoverable" faults. We have seen designs where the generator's reverse power protection tripped a lockout that tripped the turbine and breaker. Operators would take a unit off line by backing down the steam until the breaker tripped, which is a good practice in itself. But they had to reset the lockout evey time they started the unit. This taught them that resetting 86 devices is a normal daily operating function. That led to another problem. ( Fortunately, no one was hurt.)

We roll lockouts on MV motor ground faults and short circuit trips but not over-temperature or over load trips. We do latch the relay trip output so the operator has to at least go to the relay where he might see the trip alarm before resetting.

 

[potteryshard]

Might the original query regarding a "digital lockout" been a misstated reference to an Electroswitch 24 series smart nameplate?

Other than that, I'll add my voice to those insisting that 86 devices have mechanical contacts. I see the lockout as "end of the world" protection: Maybe the protective relay is on fire; maybe an arcing primary fault has migrated to a CT secondary... I'm simply more comfortable with last-ditch protection relying on large contacts and big conductors.