What is multiplexing in protection relaying?

[electrical429]

I understand what multiplexing is, i.e. transmitting several different signals via one channel. I just want some practical examples.

1. Assuming we have 96F fibre cable, which comprises 96 fibre strands. We can either connect 96 relays via this fibre cable directly. Or we can connect all of them via 2 (transmit and receive) fibre strands using multiplexer. Is that correct?

2. If relays utilise IEC 61850 communication protocol and are connected via ethernet switches at both ends. Does ethernet switch in this case counts as a multiplexer? Will it also utilise only one (or two?) strand in that 96F cable?

 

[thermionic1]

Every FO circuit I've worked on has 2 fibers - Tx & Rx. This is true in both direct OPGW and on a multiplexed circuit. In a POTT or DCB both relays need to be able to send and receive. I suppose a DTT would only need to send at one end and receive at the other, but that brings up channel monitoring. Typically with a Tx/Rx each relay looks for a receive (like a guard signal) and is monitored by SCADA.

The multiplexers I normally work with are the SEL Icon and they are all set up with Tx & Rx from each relay. From there it goes out two separate paths, each with a Tx & Rx. We do have some ICON's that only have a single path and I think the networking guys refer to these as sticks. This is generally a temporary configuration as the SONET rings are built out or if any fiber repairs or reconfiguration of the fiber paths is performed.

As far as I know, 61850 was designed to stay in the station. I did hear of some weird events when a mobile station was moved and 61850 bits were sent / received at the new station (not a desired operation). I think you need both for handshaking, etc.

Check with SEL on the ICON and GE on the JungleMux for more info. The multiplexing these devices do is to combine signals from multiple relays out to a common pair.

 

[JG2828]

1. Assuming we have 96F fibre cable, which comprises 96 fibre strands. We can either connect 96 relays via this fibre cable directly. Or we can connect all of them via 2 (transmit and receive) fibre strands using multiplexer. Is that correct?

Each relay would use 2 fibers (TX)(RX), so you would only get 48 relays at each end communicating over 96 fibers.
For things like line current differential, we usually use a channel bank (Zhone IMACS) to multiplex the C37.94 serial over fiber communications channels from the relays. It comes out as a channelized T1 connection which is sent to the other end of the line by either an SEL ICON fiber multiplexer(SONET ring), or a microwave. You can also get C37.94 cards for the SEL-ICON and skip the channel bank part.