Digital relay push button functions

[thermionic1]

We are designing a relay upgrade for a client. I was reviewing existing and reference schematics and was looking for controls for functions like 79 and POTT (comm), which made me consider that this utility may be utilizing relay push buttons for these functions.

In our region, for whatever reason, we still prefer cut out or control switches for reclose enable (79CO), trip/close (101), local/supervisory and comm disable (85CO) on the transmission system. We have HMI's in the station but they are for indication only. Our local disco has moved to all soft points (via HMI) for similar functions. Our SEL 400 series do not utilize any programmable push buttons. This approach obviously ups the parts count, wiring & real estate on a panel.

I'm curious what others do any why. I'm also curious to what extent others integrate SCADA functions into relays. We use SEL relays for metering and I see others using a dedicated meter.

 

[dpc]

For distribution substations, we've used the relay pushbuttons for trip/close, reclose enable, hotline tag, etc. for quite a while. There is generally LOCAL trip/close at the outdoor breaker and of course, mechanical trip. We do still sometimes use a separate hard-wired SCADA cutout switch but it's just an input into the relay so it could as well be a relay PB. Cost savings are substantial, but there are only so many buttons available on the relay.

For metering: I prefer to have an analog ammeter on the transformer secondary or primary just as a sanity check. And an analog voltmeter. But I'm old. Otherwise we use the relays for metering. If you're talking about revenue metering, that's a different story - separate CTs and PTs. Not many relaying CTs are revenue accuracy.

 

[HamburgerHelper]

It stays that way to make it simple for the techs and it is harder to make a mistake with a push button or lockout. SEL was trying to use their relays to also 86 lockout pieces of equipment. That got a hard no even if they have a fail mode state. I would keep it simple and dumb for the technicians. They are the ones that have to go out there two in the morning to the substation.


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If you can't explain it to a six year old, you don't understand it yourself.

 

[bacon4life]

-In distribution applications we have moved to using SEL push buttons for trip/close, 79 and various other controls for similar reasons that dpc mentioned. Lockouts are still hardwired. Transmission panels still have discrete switches, in part because the transmission panels have A/B relays where neither relay is primary. In distribution applications, we tend to have a single primary relay and rely on the bus/transformer relaying for feeder backup protection.

-We have also moved to using relays for both displaying analog values locally and for sending analog values back to SCADA. Many transformer relays have only CT inputs, so we need a separate meter

Though there have definitely been lessons learned along the way, the reduction in hardware and wiring costs is quite dramatic.

 

[dpc]

Yes, we keep the traditional 86 electromechanical lockout relay for the main transformer lockout. For a lot of reasons. At least so far. But no separate 86 relays for the feeders.

 

[beyond86]

We use push buttons for enable\disable some functions of protection at substations 500 kV. IED GE UR.
We had some problems with it. Duty personal forgot to enable functions of protection after an immobilization and when there was a short-circuit, backup protections worked.

 

[cranky108]

Just a thought, but if the relay dies, what do you need to control?

Trip/close should not be depend on relay health. Same with local/scada. Reclosing already depends on relay health, so it's game.

Microprocessor lockouts are not a good idea, when the old type work well, and can be seen that it is locked out.

 

[bacon4life]

For trip & close control, some SEL relays include large red/green buttons that are independent of the microprocessor but still in the same overall case. I definitely would be concerned if the only way to trip a breaker was using on of the regular pushbuttons on a relay.

 

[dpc]

If the relay is non-functional, why would you be closing the breaker? For emergency tripping, there is always a mechanical trip. For outdoor substation-type breakers, we do specify local close/trip control and a local/remote switch at the breaker.

 

[cranky108]

For an outdoor breaker, we disconnect the close function, and in case of a loss of gas we disconnect the trip.
The outdoor switch can not access the sync-check, local/supervisory switch and lockout block closes, so it is a risk to allow it to be used.
Besides, do not operate tags only need to be applied to one location.

In many of our applications, we use two protective relays, so we can keep a line in service even with a failed primary relay.
We would not put trip and close on the secondary relay, as this would be confusing.

 

[dpc]

We would not put trip and close on the secondary relay, as this would be confusing.

I don't really agree, but there are a lot of considerations, obviously.

I spent 8 years developing logic schemes using SB-1 switches and I really have a lot of affection for them. But I think it's really hard to justify using them in the large majority of breaker control applications at this point. YMMV.

 

[thermionic1]

Well we heard back from the client and indeed push buttons will be used for MB POTT enable and reclosing enable - only. The reference schematics will now be updated to reflect this soft logic as it was not intuitively obvious when viewing them. For the push button functions, a soft point will go to SCADA as feedback of the status and an alarm.

The next challenge is that the TT function comes through the SEL relay via MB fiber. The relay already trips both line breakers and blocks reclose. Why are we then using the same SEL to hit an Aux relay to do the same thing???

The customer is always right and they don't want to hear when they are not

I feel that some control switches are useful, beyond their intended function. For example a Local/Supv switch , while in Supervisory, can save someone from bumping the 101 (Trip Close) switch. It's also convenient when doing any physical wiring on the Trip/Close Aux relays or I/O units. Additionally, it's nice to be able to place the station, or parts of, in local when doing function tests related to SCADA upgrades. I just recently heard a horror story of a station being dumped, feeder by feeder, due to incorrect SCADA RTU to EMS mapping.

 

[cranky108]

Maybe the TT function, which needs to hold until the remote end is reset (some schemes may be different), can't do that without indication that it is being held.
It also could be a testing thing, or an operational procedure.

You can also hang a tag on a physical 43 switch, and it is difficult to do that on a soft switch.

I have had problems with 'cutoff' switches, as people are confused by 'ON' and "OFF'.