By-Passing Circuit Breaker trip- Is this possible

[WiringBoy]

Hi,

This might be more of a controls related question. I have attached a pictures which has two schematic.

1. Existing Schematic
2. Planned Schematic

My Distribution utility shares substation with the transmission utility. Bus protection and bus is owned by transmission utility but our distribution utility owns the feeders and its associated protection.

Existing Schematic shows the main trip that is from the feeder relay and Aux Trip1,Aux Trip 2, 3 & 4 show coming from the transmission utility to trip our breaker directly. These trips could be from Bus diff., bus back up or any other protection scheme. Blocking is shown to block tran.utility trip.

My objective is to determine if transmission utility issued a trip to my breaker, and that is shown in the Planned Schematic. it is like taking + ve and -Ve and then feeding to a digital controller just to detect if a trip was issued from transmission utility.

But I dont want to detect my own trip because my relay would tell me that. Would this work ? Any suggestions please.

 

[pwrtran]

What kind of relays are used?

 

[jghrist]

It looks like your scheme would assert the SEL-3520 input when there is no trip contact closed (Main Trip or Aux) and de-assert when any contact is closed (shorts input). The input is shorted (de-asserted) for any trip. It would also be de-asserted when the breaker was open for any reason (52a open). I don't think this is what you intend.

 

[xnuke]

I agree with jghrist - this isn't what was intended, because any trip will cause the input signal to the SEL relay to go to zero potential. There is no way to differentiate which trip contact closed.

One question - if your own relay can tell you when it caused the trip, wouldn't the existence of (trip and no locked-in target from your own relay) inform you that the trip came from the utility?

xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[mgtrp]

Place a blocking diode in series with the utility trip signal, and then you can differentiate between the utility trip and your own trip (if you connect the +ve side of your input to the upstream side of the blocking diode, and the -ve side of your input to the -ve rail, it will pick up whenever the utility trip is issued.

Alternately, if you can live with a small amount of delay in the trip signal, have the utility trip activate an interposing relay, rather than tripping the circuit breaker directly. One contact of the interposing relay trips the breaker, another gives you a trip indication.

Alternately alternately - perhaps the best solution - is to see if you can get the utility to provide you with a trip indication signal directly from their relay (fairly simple if they're using a numerical relay with some spare outputs).

 

[pwrtran]

SEL 3530 can be implemented as an RTU and/or HMI that communicates to the scada master. When you indicate SEL3530 I also assume that other relays are IED type otherwise there is no meaning to use SEL 3530. So wouldn't you implement the trip targets by using the DNP or IEC61850 communication and relay logic?

 

[WiringBoy]

Thanks Main relay is a SEL 351 and Aux. relays from transmission utility are old electro-mechanical relays.

mgtrp, I like your idea of using a diode, could you please be kind enough to draw a schematic and show it to me.

Thanks

 

[DiscoP]

Could you use a current operated aux relay, for example the MCAA from Alstom, placed at the location where Sw1 is shown.

 

[WiringBoy]

Is it acceptable practice to have a current operated relay in series with a trip circuit ?

 

[pwrtran]

Wire each electro-mechanical relay trip contact in to SEL351 input and assign another output contact for the external trip signals, that way you can have the SCADA alarms and front panel LED's and integrate to your SEL3530.

 

[DiscoP]

Not sure where you are, but if you have ever used a CDG o/c relay with a series seal-in unit, you've used this relay in series with a trip circuit. These relays have got an excellent service history.

 

[DTR2011]

Using pwrtran's idea you also have
the benefit of SER reports on the SEL 351 and 3530.

This also provides a nice way to test the Aux Relay and document it.

 

[mgtrp]

Sketch with diode below:

Using the SEL-351 as an interposing relay could also be a good solution.

 

[WiringBoy]

Thanks Mgtrp. I just have tweaked to reflect my situation. As the right side is auxiliary trip. Please see attached. It is a 125 V DC system, Could you please suggest me something on Diode specifications.

I was advised by one of my peers that it might be good idea to have a resistor in parallel with input. What do you think ?

Any fallback of this method, what if a diode has to fail, what would happen?

 

[pwrtran]

WOW, that could be a very risky!
You don't want anything parallel with the trip coil, be cautious that the "digital input" may disable your trip coil!
Also, that is 30 years old method and it does not match your data concentrator application, or you wast your money on it!

 

[mgtrp]

Use of a diode in the trip circuit is not uncommon even today, especially in circuits that have a number of non-electrical trips (transformer trips, generator trips, etc) that need to be individually annunciated.

A failure of the digital input would not disable the trip coil, only the trips on the upstream side of the diode. The two most common failure mechanisms on a modern protection system are human error (bad settings) and output contacts - routing all of the trips through a single relay hardly reduces your risks as compared to worrying about the possible failure of an input.

For all that, I don't have any issue with the suggestion of routing the trips via the SEL-351, there are a number of benefits such as event capture that can be realised. I use both methods, depending on the application.

With regards to diode rating - the reverse voltage should be well above the nominal voltage of your system, but the diode continuous current rating doesn't need to be as high as the trip coil operating current since it is momentary only. Good diodes are cheap, failures can be expensive.

 

[WiringBoy]

Thanks to All. Appreciat the comments. I think I will go with interposing relay option. I am trying to find interposin relay with very short operating time and which is used for breaker tripping interposing operation. I have looked at ABB RXMS1 but it canot break enough current. Any suggestions please.

 

[DTR2011]

Have you worked with the RXMS1 before? IIRC, you need a rack mounted chassis and a special tool for wiring this thing up. Wire checking is not easy to identify. If you want to go that way, I believe the ABB Type AR has similar trip time with a more user friendly foot print.

As mentioned above you can use the SEL 351 as your interposing relay. Wire each of the existing Aux relays to inputs of the SEL. You can then map those inputs to the main trip output. Set up your event reports to capture this information and there is no guessing who tripped your breaker.

 

[WiringBoy]

http://www05.abb.com/global/scot/sc...RXMS_1_RXSF_1_RXME_1_RXME_18_RXMH_2___RXM.pdf

Above link shows a tripping assembly marketed by ABB.
The schematic is shown on page 18 fig. 5 . I can reduce pickup time of my interposing relay by RXMS1 and breaking by RXMH2 relay. I would appreciate your input if any body has used this before.
Thanks

 

[mgtrp]

A couple of comments on your proposed scheme:
1/ Old electromechanical relays often require a certain amount of current to flow to pick up the seal-in coil, which in turn drops the trip flag - please be aware that the utility may no longer be able to tell which of their relays initiated the trip, as the auxiliary relay coil will not draw enough current.
2/ Generally, you do not need to interrupt the trip coil current with the relay contacts, that is what the 52A contact is for. You do need to make sure that the relay contact stays closed until the circuit breaker opens, however. One way that I have seen this achieved with interposing relays is to use a contact from the relay to seal in the relay coil, and then a 52A contact to drop out the relay coil.
3/ I'm not sure if you've worked with the ABB relays before, but if you're not used to them they are kind of a pain. You need special terminations for the wire and some additional tools to install/remove the wires. The relays can be installed in a Combiflex rack, which aren't too bad to access but will need to be panel mounted, or can be installed in a DIN-rail socket inside your cabinet, which from what I've seen need to be removed to work on. That being said, the ABB relays are otherwise excellent in my experience.