Direct Transfer Trip (DTT) signal through Multiplexer

[rockman7892]

I was working on a project recently where a utility was expanding an existing multiplexer (GE Junglemux) and adding an expansion card to integrate a new DTT signal from a remote station.

The multiplexor was connected was connected to a station router along with an Orion LXM, an SEL-2100 and an SEL-2440. The multiplexor also had direct connections to the SEL-2100. It was explained to me that the SEL-2100 was being used to pass mirror bit signals for DTT tripping to the SEL-351 relay associated with breaker designated to trip.

Substation comm networks are somewhat new to me so trying to understand if this application is typical to have various hardware devices described above to support substation commm and control. Since I'm not that familiar with Substation comm's there may be standards or reasons (like not putting all eggs in one basket) that there are mutlipe devices supporting comm/control even though it appears to me like a sigle device (or alot less devices) can accomplish the same thing.

1) For example what is the typical role of a multiplexor in a Substation? Could a DTT trip not be recieved directly by the RTU and pass comm signal directly to SEL-351 (mirror bit or hardwire output) for tripping breaker?

2) The SEL 2440 in this application appears to simply be used for hardwired I/O from field devices? Couldn't an digital I/O card on the Orion RTU accomplish the same thing?

3) I'm not that familiar with the SEL-2100 device but it appears to be a logic processor. Again cant whatever logic it is providing typically be provided by RTU or devices?

4) Is it typical to have a router vs an ethernet switch as the main gateway for the Substation?

 

[thermionic1]

The typical role of a multiplexer is to send & receive protection signals. The JMUX and SEL ICON are both popular devices that facilitate a SONET ring network. The signals are carried at a high speed, dependably and securely. Sonet networks have the ability to self heal, by automatically rerouting signals in the event of a channel failure. A SEL Icon, for example can reroute a signal in about 5ms. Many Sonet interfaces carry DTT, POTT or line differential data. Additional cards can be installed to carry video, telephone, etc. The reason to use a Sonet ring versus an RTU is both speed (<1ms latency) and deterministic timing. The RTU may be able to send the signal, but it could be 40ms, it could be 16ms or it could be 90ms. That DTT from the remote end could be a failed breaker that needs to be isolated NOW. Previous communications based channels include Audiotone, which had issues (leased lines) and the teleco's have all but removed copper from their system. Powerline Carrier is still popular and more economical in some situations. Many EHV lines may have Powerline and either direct FO or FO via Sonet.

The cards on the Orion are for serial communications, such as RS-232 or RS-485. The 2440 can read hardwired alarms and then send this data out in a number of different communications protocols such as DNP, SEL, MODBUS, etc. The RTU reads the data either via ethernet or one of those serial ports. The Orion reads that and does what it's programmed to do. The RTU can also send commands for the I/O to act upon in the same data cable. If an alarm for low gas comes into dispatch at 12:01 vs 12:00 it's not a big deal. Same goes for say operating a cap bank.

The 2100 reads SEL mirrored bit devices. There are a number of these products that are remote I/O, speak Mirrored Bits (MB) only. Small surface mount versions are ~$600. Mount one in a breaker, wire to relay alarms and send 1 pair of fiber back to the house vs. 8 pair of shielded cables. The 2100 can then translate MB data for alarms and translate to DNP to be read by the RTU. MB is a peer to peer protocol, used in SEL relays for about 20 years. Simple to implement, fast and provides channel monitoring. The 2100 can read MB and then route the data to a number of connected channels.

Yes.

 

[davidbeach]

An RTU is a SCADA device, not a protection device. The two should not mix. SCADA is generally to slow and not sufficiently deterministic to use for protection comms.

I’ll see your silver lining and raise you two black clouds. - Protection Operations