Trip circuit supervision relays, anyone have experience using these? Are these common? 1

[bdn2004]

I am in the middle of a project that is requiring some re-design of the control circuit provided by the Vendor. All we required is a simple system that on alarm will trip our main breaker. This Vendor however has put in a few more electronics...such as this supervision trip relay. ABB SPER1B1C4. Apparently this relay will force through a small current and monitor any changes in resistance, any changes and this outputs an alarm.

Doesn't this trip circuit have to be a normally closed circuit to be able to force through this small current and doesn't have to know the actual impedence to work correctly?


Also, this is supposed to work on the trip coil of a medium voltage breaker. The main coil is a 1/2 mile away from this location. We have an interposing relay that activates this breaker. It's connected to lot's of other stuff too. We don't have this on anything else that I am aware of in this plant. I'm tempted to just take this out altogether, but then again if it's worthwhile why not leave it in?

 

[rasevskii]

In the classic design, the high-ohmic coil of the trip supervision relay is connected in parallel with the final tripping contact. The current is only some mA if the main trip coil circuit is intact. The trip coil itself has to be low ohmic.
If the trip coil circuit is for some reason open (such as the breaker being racked out) the trip supervision will drop out, giving an alarm.

Downsides: (1) the trip supervision will give an unwanted signal when an actual trip occurs. (2) It may not work with modern high ohmic electronic trip systems (3) it will not detect a shorted trip coil..

rasevskii

 

[rcw retired EE]

You could leave it connected to monitor the integrity of the auxiliary tripping relay circuit. It would not monitor the actual breaker trip circuit. Depending on how onthe connections, it may also alarm on loss of power to the auxiliary tripping circuit. Do you have an alarm panel or DCS that can accept the alarm?

Before solid state relays and unmanned stations, we used the red "Breaker Closed" light for this function. The high resistance bulb was connected across the open trip contancts and trickeled milliamps through the trip coil and its 52a contact. If the red light was out, we checked the trip circuit. These modern relays provide the same function and give an alarm contact output.

 

[bdn2004]

rcwilson,

"Do you have an alarm panel or DCS that can accept the alarm?"
This is actually connected to a PLC that runs this piece of equipment. The PLC in turn will light up a board that says there is either a trip or an alarm.

The Vendor has responded and said they make this a mandatory requirement because they had a situation once that their equipment actually sent the signal as required...but the trip circuit was fouled up in some way and the signal wasn't received on the breaker end ....and it all melted down. Smoke. Lawsuits. Yikes.

I appreciate the old school way of doing this though...as most of this plant is still run - quite reliably I might add - with mostly hardwired relays and limited electronics. Do they still make these "red breaker closed" lights?...or is that just too an obsolete method and everyone is changing them out to electronics?

I just worry about introducing new fangled things, especially black boxes that can shut us down and there is not another one on site, therefore no one has ever had to work on it. The simpler, common, straight forward things are usually better - when possible.

Thanks all for the input.

 

[rcw retired EE]

These lights are standard products. Some have a current limiting resistor moutned on the back, some require special bulbs. I haven't specified any lately, we leave that up to our panel and switchgear suppliers.

One product I used for retrofits was made by Emax. It is a minature relay replacement for the red trip light. It fits in the same hole, has a red LED plus a contact output that operates on loss of power or loss of trip coil trickle current. Put one of those on the "real" trip circuit and you may have a complete system.

 

[ppedUK]

There are many forms of supervision circuits and they are quite common (at least here in the UK) and have been for many years. Some of the more complex supervision circuits monitor a large portion of the trip circuit (including the external trip circuit cabling in some cases), not just the trip coil.

Depending on the type of supervision relay used, the relay can monitor the trip coil before closing of the breaker and also whilst the breaker is closed, but none of the schemes I have come across are actually configured to trip the breaker, just alarm only. If the main trip coil has failed then you would need a second trip coil to be activated from the supervision relay if that's what you are trying to achieve.

Some of the modern electronic protection relays have built-in supervision and can be configured to inhibit closing of the breaker if the trip coil has failed (Pre-close supervision), but most of the circuits I deal with rely on good old electromechanical supervision relays which can also be configured such that an alarm is not activated when the breaker is actually tripped, in fact some of the more complex supervision circuit requirements (H7 type in the UK) cannot be accommodated using the built-in supervision in electronic relays.

Your vendor has put in a "new fangled" trip supervision relay for good reason, so why do you see the need not to use it just because you don't understand how it should work? You should be trying to incorporate it correctly in your trip circuit.

 

[bdn2004]

ppeuk,

Thank you for your comment.

It was ironic when I was thinking if I would respond to your post that my computer seemingly froze up, the the wireless mouse stopped working. I thought I had replaced the batteries fairly recently and was thinking I would have to re-boot my computer and lose about 2hrs of work that I had done. Thankfully it was the battery and I didn't lose anything. But what if I didn't have any spare batteries? Trip to the store. What if they were out? I'd be dead in the water and either way inconvenienced. But I would experience none of that if I were using the tried and true conventional corded mouse.

We don't have ANY of these that I am aware of on the hundreds of circuits that can trip these breakers in this small portion of this very large plant. And this device uses a voltage that requires a power supply, the vendor has even suggested a battery backup system (more $$ for eternity) for that power supply. You are right, this doesn't trip - only alarms. But will our maintenance people know what do if when it alarms? Doubt it. On the other hand, RC above suggested a simple coil with an LED that could do the very same function - why not do that if we must have this circuit?

We are working with the Vendor for a solution that works for us both. One that doesn't void their warranty and fits in with the sophistication level of our existing system. That was always the plan, I just wanted to suggest an alternative system in a sketch form. We may however end up with this, I'm not knocking it, it's obviously a very good product or they wouldn't be using it...just questioning it...which is what I'm supposed to do.

 

[LionelHutz]

How do you handle a failure to trip for the 100's of other circuits in your plant?

Here are questions to first answer. Assuming you leave this out, what would you do if this breaker fails to trip? Now, with trip coil monitoring what would you do if you know the breaker won't trip? Can you make the system safer using trip coil monitoring? You need to know what you will do operationally before determining if you need trip coil supervision. Your protection systems may have a staggered trip configuration to protect against a failure and that may work well for your plant. The relay is quite pointless if you won't gain any operational or safety benefits.

That trip coil monitor will just tell you beforehand that attempting to trip is pointless. It won't do anything else like trip another circuit.

I do like the idea of wiring the closed pilot light across the trip contact, but you would have to use that plant wide and ensure everyone knows the closed light being out could mean the trip circuit has failed.

 

[bdn2004]

Lionel,

If you read the last part of my original question... We have control over 86 lockout relays that trip the main breaker(s) that are located 1/2 mile away at a power plant. These are medium voltage oil filled circuit breakers in a switchyard. I say breaker(s) because these circuits can be fed from different primary sources depending on how the system is configured on any given day. I looked at some of the schematics of some of these breakers, some have two trip coils, some don't.

As far as I know there has not been any issues with failures to trip these breakers from our side. I have not dug extensively into the power plant drawings. They may even have a whole slew of these relays! But we don't have any - and that is all I am concerned with.

These breakers are tripped fairly routinely with these lockout relays for scheduled outages. We use walkie talkies to be in communication with the power plant when we do that. The only thing I see these monitoring are these trip circuits that go to these 86 relays. From what I've read about these relays you need one relay per contact - yikes. That expense would never fly.

And remember too from my original post, the Vendor originally thought we had a new dedicated main breaker locally, right ahead of his equipment. That was the original design, but it is not any more - we are to trip the main breaker at the power plant...which is how everything on my side works. I am trying to provide them a sketch of what we want.

 

[LionelHutz]

Hmmm, that's a fair bit more info despite it being "part of my original question".

I guess you didn't understand the point of my questions. You say "we are to trip the main breaker at the power plant". I would assume this trip will prevent the smoke and lawsuits. So, what will happen if that breaker does not open when the protection relay signals it to trip? This is the question you need to answer. Only then can you decide if the trip coil supervision relay can help avoid the smoke and lawsuits.

The other thing about trip coil supervision is that knowing the trip coil circuit is healthy does not guarantee the breaker will open.

 

[bdn2004]

Lionel,

I don't really know how we handle a failure to trip because as far as I know they always do trip! But I'm actually not the one directing this activity and haven't been here for years and years so I don't know if that has ever been an issue. I'm going to find out - thanks!

Are these medium voltage breakers notorious for failing to trip? Then I could see the purpose of installing these supervision relays, even retrofitting the plant with them. Then again, I'm also always on guard for trying to prevent a once in million catastrophic failure where there is questionable return on investment.

A failure to trip could be a big deal especially if some critical piece of equipment is in the process of melting down.

 

[bdn2004]

I guess I should have said...are these trip circuits notorious for getting fouled in some way to prevent a clean signal to trip the breakers across industry? And this wouldn't tell us that we sent the signal but the breaker didn't trip anyway.

 

[rasevskii]

You might want to consider also a breaker-fail relay that will trip one or more upstream breakers if all else fails. That would be better than a meltdown and the smoke and lawsuits...

rasevskii

 

[collies99]

Lionel,

As per rasevskii failure to trip during a protection event is best backed up via a breaker failure function. A breaker failure relay have a delay setting at twice the normal breaker tripping time and becomes part of the local back-up protection scheme.

Breaker failure is your first back-up protection and will be faster than up-stream back up relaying time. Breaker failure is only initiated via protection and each breaker should have one. Breaker failure will not initiate for failed breaker tripping from controlled openning command since it does not involve any protection event.

Hope that helps in the discussion.

 

[odlanor]

there is a fee that the utility receives for reducing the generation dispatch. This penalty is 18 times higher if the Interconnected Systema is not warned!
It is best to install coil monitoring....

 

[ppedUK]

bdn2004,

It all comes down to................what is the risk to your plant if the breaker fails to open. There is talk here of smoke and lawsuits and I'm guessing that this thread is related to your earlier thread regarding the equipment manufacturer's requirement for two trip coils (one permanently energised) in your breaker. My guess is that the manufacturer of your kit is concerned more with the loss of the tripping supply and / or trip circuit wiring integrity than the trip coil failing or the breaker failing to open mechanically, that's probably why they were / are requiring the trip supervision relay or the previously suggested UV release coil.

MV breakers are generally reliable pieces of kit and as you imply, failures are rare, but failures of tripping battery units / tripping fuses / tripping circuit wiring are far more common and hence the requirement to have trip circuit supervision if you cannot fit the UV release coil.

With the high integrity supervison schemes you can check that the trip circuit is healthy before you close the breaker and inhibit closing if it isn't. If the trip circuit fails when the breaker is closed and you have a plant alarm to warn you of that event, then you (hopefully) have a bit of time to think what to do before the breaker needs to be tripped in anger. If you have a simple lamp (very basic supervision), you have to keep sending someone along to the switchroom (or wherever) to check it, but if your maintenance people don't know what to do with an alarm, then they wouldn't know what to do when a lamp is out either!

 

[odlanor]

I do not agree! I guess There are operating procedures that establish the tasks to be performed for different types of alarmI

 

[bdn2004]

ppedUK,

If the breaker fails to open it could be a disaster no doubt, but it could be a disaster now with all the other equipment we have been operating successfully for decades. That's my issue...why now, why is this so special?

The circuit works just like you posted. I guess that is the norm nowadays which really was my question. The coil method though I like better, just because it involves less stuff - and we could paste a permanent phenolic sign by that light telling the operator what its for and what to do.

We're going to end up with this just because the Vendor will not warranty it without it. But it is nice to know the logic surrounding it's existence that this discussion has provided - THANKS!

 

[ScottyUK]

One possible reason why it becoming more important is the increasing interval between maintenance. Years ago maintenance was carried out frequently enough to ensure that failure due to the passage of time was uncommon. Today the trend is towards maintenance intervals approaching that where failure due to the passage of time is a real possibility. Of course that logic doesn't account for problems introduced by maintenance, but other things being equal if you increase the period between maintenance then you arguably need better monitoring as the probability of failure increases.