Close and Trip Relay

[alivip]

As you know, in Protection system we usually use close and Trip relay between Main relay (as commander) and circuit breaker.
These relays must have to main features, Heavy duty and high speed.
The main use of these relays is that, when main relays (for example Distance relay) sends trip to CB, about 4ampere are used by inductor of CB.
hen the relay contact wants to break this current ,it must withstand Ldi\dt voltage . this voltage usually results to destroy main relay contact.
So, based on this philosophy which above mentioned, we use trip and close relay.

After improvement in CB mechanism, the CB contact position is used in the path of relay and CB coil. So the trip current is broken by this contact (for example after CB is tripped, the CB will be opened, so the CB contact will be opened and breaks the trip current)

But we still use trip relay and close relay between main relay and CB,,why?
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For example we use 7PA27 Siemens relay as Trip relay and 7PA23 Siemens relay as Close relay.

I know just one reason.

 

[dpc]

SEL makes surge suppressors and they seem good, but there are other products that can be used. I can't say we always use them, but if there is concern about the robustness of the output contacts, then the surge suppressor is way to reduce the wear and tear on the contact.

I have seen some PLC outputs welded when used to trip just a lockout relay.

Also, if using interposing relays on a trip circuit, make sure they are extremely high quality. I have seen installation of some really wimpy interposing relays that were much less capable than the contacts they were supposedly protecting.





David Castor

http://www.cvoes.com

 

[slavag]

Once, I calculated price for such high trip relay ( must be a high speed relays, with 4-6ms make time)...for exmaple 6pcs. per one distance relay, with two trip coils and single phase trip, cheaper bay one spare card for numerical relay.
and number of CB faults today...near to zero.
last project, I used a very cheaper trip relay= 90Euro, please add wiring and place into cubicle.

 

[alivip]

So, Conclusion is :

1- the only use of Trip and close interposing relay is : To prevent damaging contact relay just(and just) in breaking the trip current when we experience CBF faulty.

2- number of CB faults today...near to zero.

3- Some consultant spec and clients still insist on using interposing relays

4- one of alternative relay : using power contactor parallel to main relay to coil (lz5pl scheme )

5- the price of using siemesn interposing relay for one CB (with 2 close coil )is about 600Euro.

i also don't understand about SEL Co. solution. is it possible to give me more detail information for this purpose.?

 

[alivip]

So, Conclusion is :

1- the only use of Trip and close interposing relay is : To prevent damaging contact relay just(and just) in breaking the trip current when we experience CBF faulty.

2- number of CB faults today...near to zero.

3- Some consultant spec and clients still insist on using interposing relays

4- one of alternative relay : using power contactor parallel to main relay to coil (lz5pl scheme )

5- the price of using Siemens interposing relay for one CB (with 2 close coil )is about 600Euro.

i also don't understand about SEL Co. solution. is it possible to give me more detail information for this purpose.?

 

[JG2828]

alivip,
Here is a link to the SEL device that dpc was referring to:

http://www.selinc.com/WorkArea/DownloadAsset.aspx?id=2956

 

[alivip]

Jg2828 : thank you.
if anybody works with SEL products , i like to have a compare with Siemens scheme about our topic subject.
i upload a file containing single line diagram of O.H.L
AS you can see, it contains :

3 trip relay for coil one
3 trip relay for coil two
1 close relay for CB close coil
1 lockout relay
3 trip coil supervision(TCS) for coil 1
3 trip coil supervision(TCS) for coil 2

the price of the following relays will be about 1300Euro based on Siemens products.
is it possible give me the same scheme based on SEL products?

 

[dpc]

Really you should just contact SEL if you are interested in their products. They will be more than happy to look at your application.



David Castor

http://www.cvoes.com

 

[odlanor]

Allivip,
in my thinking, a CBF faulty in 500kV-CB with trip coils of 500W to 800W, the main relay 7PA27 contact will be damaged and TCS 7PA30 will verify that the Trip Coil are OK.
It will be necessary a visual inspection of the contact.

I guess this is not the purpose of the surge suppressor.

 

[alivip]

I dont know the exact use of surge suppressor , i will ask someone.
anyhow as you said

TCS(7Pa30) use is : supervision of trip supply path of trip coil. it is used in closing CB interlock. if any fault exists in path of trip the TCS contact will be opened and the CB can not be closed (because in fault condition we can not open it).

Trip relay(PA27) : interpose between main relay and CB coil to break the trip current. it prevents damaging main relay contact.

 

[slavag]

External TCS today is not must.
Possible use build-in 74 function into Siemens relay ( or other ), but you need additional binary input for every trip coil.

 

[odlanor]

alivip
excuse the mistake. In fact I never saw project with protection relay is used directly in the trip circuit. Always interposing relay is used. (94)
It is very popular to use the relevant set of fast relay RXMS1 ABB in parallel with AREVA-CS1C contactor.

I would like to know how to check if the trip relay(94) is suitable to prevent damaging contact relay during CBF faulty.
Assume a trip circuit for a 500kV CB with a trip coil of 2.5 ohm in serie with resistor of 20 ohm .
Trip relay(7PA27)data:
40A-0.5s-110VDC
1 contact non-inductive 125VDC- 1.2 A - 20 ms
1 contato inductive 125VDC 0.6 A - 20ms
Will be PA27 suitable?

 

[davidbeach]

Why would the relay output contact be damaged on breaker failure? All you have to do is set the trip unlatch condition to be breaker open and then the relay output contact will not open until the breaker opens, even if that is hours later.

 

[odlanor]

In transmission line protection with reclosing, a trip relay can not be latched relay type. After an operation of breaker failure scheme, with elimination of the fault, coil of relay will be desenergized and contact relay will opened by the spring return.

 

[davidbeach]

There's no reclosing on breaker failure, so that isn't a concern. I'm not talking about a physical latch, just a logical latch until the breaker opens. If the breaker fails, the trip will remain standing on the relay and will be interrupted by a relay tech opening the test switch, but long before then the trip coil will have interrupted the circuit by burning open, so still no issue. There is no need for any type of interposing relay between the protective relay trip output and the breaker trip coil. To do so is just to reduce reliability.

 

[alivip]

odlanor :
yes, based on Siemens answer you can series contacts of 7pa27 to reach this capability ( i think 3 set is required)

davidbeach :
it will be unlatched because when cbf is started other cb (connected to faulty cb ) will be tripped and they cleared the fault so trip will be unlatched.

other note : there is not only main relay tripping to cb, consider that re closing relay and discrepancy (or push button) also command to open cb .

 

[davidbeach]

If the unlatch condition is breaker open, opening other breakers won't unlatch the trip.

ULTR = NOT 52a

Simple enough.

 

[slavag]

Not in all cases used latched functionality, for example autoreclosere case .
Not in all cases to protective terminal is connected 52a signal.

Lot of versions.

And not always 52a contact is same position as main 52 contacts.

 

[odlanor]

My conclusion is that the need for interposing relay is due to CBF faulty, at tripping circuit where 52a is used to break the trip current.
Based on the reasoning of David,I present a general solution. Tripping will be made by 2 contacts in parallel:
1 - binary output for general trip of numerical protection relay.
2 - blocking relay(86BF) of breaker failure protection applied into CB defective.
With this we'll have the compound scheme of fast and heavy duty tripping.

slavag,
Why necessity of interposing relays at closing circuit?

 

[alivip]

i don't to why we exactly use interposing relay in closing circuit.
may be when auto re close send close command and the cb close coil can not close the cb, the circuit will be opened by close relay instead of main relay contacts.

 

[jghrist]

Not in all cases used latched functionality, for example autoreclosere case .

Why not use latched trip with reclosing?

Not in all cases to protective terminal is connected 52a signal.

Seems like an extra 52a contact and an extra relay input would usually be cheaper than a tripping relay.

And not always 52a contact is same position as main 52 contacts.

By definition, 52a contact is in same position as main 52 contact. I suppose that it is possible that the breaker will fail to trip, the 52a contact in series with the trip coil also fails to open, and the 52a contact energizing the relay 52A input does open. Anything is possible, but if it is very improbable, you can live with a very rare relay contact failure.