Intertrip/Interlocking between IED which using different communication protocol

[bee79]

Dear Experts,

As per the subject, if an upstream IED using Modbus and downstream IED using IEC61850 communication, how to implement the intertrip/interlock function between them?

The upstream and downstream equipment are located very far from each other where hardwire connection is not possible and fiber optic is the only solution.

 

[davidbeach]

Some form of intermediary device that can speak both Modbus and IEC61850 would be about the only option.

 

[dpc]

https://www.selinc.com/SEL-2505/?v=2#st_options

Depends on what you mean by "very far". You would need dark fiber available to use the SEL-2505, but with single-mode, it has a range of 80 km.

 

[bohdand]

MODBUS is not designed for critical functions like breaker interlocking. For this you should use the IEC61850 protocol. A possible solution is to hardwire an output from the Modbus device and use a low end IEC61850 capable device as a converter and have it transmit the contact status via the IEC 61850 protocol over fiber to the remote site using the IEC 61850 capable IED. But even in this config there will be some additional milliseconds of delay, which may or may not be acceptable in your specific application.

If you proivde details on the two IED's you are using we might be able to proivde a better answer.

 

[slavag]

Use SEL2506 with HW connection between both IED. 8 DI, 8DO, fast and simple.

 

[davidbeach]

Or, if you want a bit more information about what happens in the link replace one or both of the SEL-2505s with an SEL-2411, a bit of over kill but with full SER capability where the 2505 provides no SER.

 

[bee79]

The distance is about 3-4km. We are still in design stage hence the IED models are not available yet.

Using a converter sounds like the feasible solution. The fiber optic cable need to go through a FO patch panel if I'm not mistaken. I need to use two/four core for the intertrip/interlocking?

 

[Marmite]

What kind of interlocking are we talking about? Is it for life safety, or just maintaining a switching sequence?

Regards
Marmite

 

[bee79]

The interlock is to prevent downstream breaker to be closed when the upstream breaker is still open. So there must be a permissive to close signal from upstream.

 

[davidbeach]

Have you considered installing a VT on the upstream side of the downstream breaker? Then you could block close on a dead line; you could even trip on a dead line. Let the power system tell you the status of the upstream breaker.

 

[Marmite]

So, do you want to know if the upstream feeder is live before you allow the downstream breaker to close? Or, do you want to know if the upstream breaker is closed? They may not be the same thing. I would consider a VT as David suggests. The simpler the better for interlocking.
Regards
Marmite

 

[bee79]

I just want to know the upstream breaker is closed and in service position.

 

[slavag]

intretrip is protection signal. it must be safety, fast signal.
you can use only dedicated devices, Im strongly not recommended use any media converters.
interlocks is additional signal, same FO

 

[bohdand]

What, if anything, has to happen to the downstream breaker when the upstream breaker is opened or trips?

 

[bee79]

For the interip protection, it's possible to use a converter for converting the fiber optic signal. Since there is no conversion of communication protocol but only the type signal being changed, the action should be fast enough. Please let me know your opinion.

 

[bohdand]

OP - Can you clarify what protocol you are referring too? You say thatthere is no conversion of communication protocol, but Modbus and 61850 are not compatible, they are two different protocols regardless of the physical layer. Are you referring to different solution (SEL devices are an excellent solution) that has been proposed? what protocol are you converting between electrical and optical? If you provide the sequence of components you are considering from beginning to end, we may be able to help you find a viable solution.

 

[bee79]

Sorry for the late reply. I'll put in point form for a better description of the problem:

1. Downstream IED must be compatible with IEC61850 as per project specification.
2. Upstream (separate power provider)IED not necessary to follow IEC61850 and they can use whatever communication protocol.
3. Intertrip/Interlock between the IED must be thru fiber due to the long distance.
4. Upstream IED not confirm having fiber optic connection port. Downstream IED fiber optic connection will be used to connect to electrical control system. Most probably there won't be additional fo ports available.

SEL device help to convert the fiber optic signal. But it didn't solve the communication protocol issue.

 

[jghrist]

It seems to me that you need to find an upstream IED that will take a 52a contact from the breaker and convert it to IEC61850. Using Modbus communications from an upstream IED would not be fast enough to meet your requirements for IEC61850 even if you could convert the protocol.

 

[davidbeach]

The SEL device solution solves the protocol problem by ignoring it. Hard wire in at one end and hard wire out at the other end. The interlocking function could be hard wired or it could happen in logic.

 

[bee79]

I can use two SEL device as davidbeach pointed out. For the interlocking signal maybe I could suggest extra core in the fiber optic cable connection between the two IED.

Or I can use the protocol converter as jghrist stated. But when you said 'would not be fast enough to meet your requirements for IEC61850' are you referring to the GOOSE messaging?