Transformer Relay Tripping Question 4

[BINGMD]

At transformer, there are tripping relays such as high winding temperature(49T), high oil temp (26Q), rapid pressure rise relay (63FP), main tank presure (63PR), Buchholtz realy (63Q) etc.

What is the traditional way for those relays tripping?
Shall those relays trip the lockout (86) directly or via another device such as the differential protection (SEL-387)?

The drawback of tripping 86 via SEL-387 is that if the relay fails, we also lost all above relay tripping.

If those relays directly trip 86, what if the contact rating (such as, 0.25A@125V DC) of the above relays is lower than 86 coil rating (such as, 4.6A@125V DC)?

Adding an interposing relay will also bring an extra failure point.


Also, if there are two lockouts (86T1, 86T2), shall the differential trip 86T1, and transformer trippng relays trip 86T2, or other?

Thank you for your response.
Best Regards,
Bing

 

[stevenal]

That contact rating is likely the interrupting rating. The 86 should self interrupt, look at the circuit diagram to see what I mean. These events a very rare also. We send the signals through routing diodes to the 86. The diodes allow separate signals to go to an annunciator so we can tell which device tripped the 86.

 

[dpc]

Traditionally, these trip contacts are run into a lockout relay. One reason for using a lockout relay is to make sure the transformer is not re-energized until someone is physically present to reset the lockout.

This "lockout" function can be replicated in a digital relay, and this is sometimes done. One advantage of this approach is that if the relay's internal processor fails, it will usually provide a FAIL alarm. But regardless of how sophisticated the relay is, the outputs are still operated by small relays inside the unit, and these small reed relay are subject to failure. In fact, these are the weak link in most digital relays. So if you use the digital relay as a lockout relay for other trip inputs, you may want to use at least two relay outputs to do the breaker tripping.

I still prefer to use a traditional lockout relay - the contacts are extremely robust compared with most digital protective relay outputs. And it can provide many more contacts if you need to trip multiple breakers, such as for a bus differential trip.

 

[BINGMD]

Stevenal,

Yes, the contact rating looks like its interrupting rating. Directly tripping 86 with routing diodes seems better for both protection and indication.

DPC,

I may misspoken my question. One opinion is transformer relay tripping 86 directly. The other is to connect the transformer tripping relay outputs to SEL-387 as inputs, and SEL-387 will trip 86, in order to have the trip function and also indication of which one trips 86. (I don't think this is a good way by comparing with the directly tripping with routing diodes).

Thank you both for the answers.

Thank you,
Best Regards,
Bing

 

[davidbeach]

I don't particularly like the diodes, there are usually enough I/O in a new design to avoid the need for diodes, which do fail over time. I agree with the 86 to hold the trip, but I also like to directly trip the breaker as well as tripping the 86.

 

[dpc]

Yes, I would vote for running the trip contacts directly to the 86 device - not through the digital relay. Sorry - I didn't read your question closely enough.

In the olden days, we used an HAA current relay to provide indication of what device tripped the lockout relay. Since it is current-operated, there should be only one flag on the HAA - the first device to pull current through the 86 coil or trip coil.

http://www.geindustrial.com/cwc/Dispatcher?REQUEST=PRODUCTS&pnlid=6&id=haa

 

[stevenal]

davidbeach,

We find the diodes to be very reliable. You can over size them for your application, and they are still cheap. No DC supply to fail, microprocessor to lock up, etc. And in this application, they seldom see any current. I've never seen a lockout relay with multiple inputs or coils.

 

[slavag]

Hi.
I would like say about few options what we use in our practic.
1. Exactly as Stevenal and Dave explained, but with one small difference. Digital relay send trip to CB trip coil1 directly and signal to LOR1 , all electromechnical protection via diodes( tens years w/o problem, we put 1000V 2-3A type diodes) send trip to High speed(HS) relay ( 4-7ms operation time)this relay send trip to CB trip coil2 and LOR2. That mean LOR1 and trip coil1 connected to DC1, HS relay,LOR2, trip coil2 connected to DC2.
2. Second option, what I very like and we used it in power stations. Two digital relays, first on the DC1 , second on the DC2, first with 87 ( diff) protection functionality, second with 51, 50 (O/C) functionality.Ground protection according to scheme. Trip contacts of each relay connected in series( on same relay of course) and each relay send trip to TC1 and TC2 ( used separated DI/O card too).
HS change over relay DC1/DC2 supply electromechnical relays
from separate MCB ( fuses) and output of those relays connected in parallel to both relays.
In this case, we didn't use LOR relay, each digital relay have LOR internal with block closing signal to CB.
Dave, you are right, problem is mini relay into digital relays, OK possible add HS relay for CB trips, but not LOR with 20-40ms operate time.
Regards.
Slava

 

[ELEP]

We experienced the same problem. SEL recommends all tripping through SEL(387) but we used Group1(86T1) for diff. & group2(86T2) for T/F supervision. Working well.

 

[BINGMD]

Thank you all for your response.

Thank you,
Best Regards,
Bing

 

[slavag]

Something intrestig.
Some countries used multibox solution, like to old application, but instead EM relays for each function used new digital relay and LOR's too.
Regards.
Slava

 

[BINGMD]

Slavag,

DO you have any document/detail regarding multibox solution and 2nd option in your first response?

Thank you,
Best Regards,
Bing

 

[slavag]

Hello Bing.
About multibox, it's standard in part of ME contries and maybe ( I'm not sure) some Japanies standard and Malasiya's standard.
About second option, no documents, it's our ( my team) solution, and we are very small team ;-) w/o any standards.

Regards.
Slava

 

[npressler]

Hello everyone,

This is my first post, so here goes.

Have any of you ever experienced a transformer trip from a rapid pressure rise relay without an actuating event to the relay from the internal rate of rise in the transformer tank? I.E. a nuisance trip. The transformer we recently tested tests good in all electrical tests, TTR, Doble< Winding resistance, megger etc. Manufacturer has tested the relay & found to be O.K. but trips slightly faster than specs.

 

[slavag]

Hi Npressler.
Welcome to the Forum.
From my point of view, you have open your thread on the issue.
Expirience of my friends from some power station.
8 UAT trafos 25MVA, each one have two such relays ( I hope, we talk about same--pressure relief relay) and from time to time they have unwanted trips. Trafos are about 25 years old. They connect contact trip of both relays in series.
Best Regards.
Slava