GE MiCOM P40 Agile, Technical Manual, Page: 513 / 962

local Ch1 Tx connects to a remote Ch2 Rx, and the corresponding Ch1 Rx and Ch2 Tx are connected together as
shown in the earlier figure (Fibre Teleprotection Connections for a Three Terminal Scheme).
This Three Terminal scheme uses a triangulation approach and is designed to function if a communications link
between two terminals is not present or is degraded. 8 duplex teleprotection commands are available between
any pair of terminals even if one communication channel fails.
Logical Channel 1 is associated with Physical Channel 1, and Logical Channel 2 is associated with Physical Channel
2.
Consider a Three terminal scheme where the terminals are referenced as Local, Remote1, and Remote2. Remote 1
correlates to Ch1, and Remote 2 correlates to Ch2. The Local terminal will send the commands that it wants
Remote 1 to act on to both Remote 1 and Remote 2. Upon receipt, Remote 1 acts upon the commands that the
Local terminal wants it to use. Remote 1 also packages the commands that it wants Remote 2 to use, together
with a copy of the commands that Local wants Remote 2 to use, and also the commands it wants Local to use.
Remote 1 sends the message to Remote2. Remote 2 acts similarly. The same process occurs in the opposite
direction around the ring, so in the event of a single channel failure, and if all terminals have the same mappings
for the 8 IM64 bits integrity will be maintained for all 8 duplex commands between connected terminals.
In a triangulated scheme, at each terminal, Logical Channel 1 commands are assigned to Physical Channel 1, and
Logical Channel 2 commands are assigned to Physical Channel 2. At each terminal, the eight IM64 commands
transmitted on Physical Channel 1 are intended for the device connected as its Remote 1, and the eight IM64
commands transmitted on Channel 2 are intended for the device connected as its Remote 2. So, eight full-duplex
commands are available between any two terminals. Each device transmits both channels of eight IM64
commands to the connected devices. At the Remote 1 device, the eight Channel 1 IM64 commands are used
directly by the receiving device which passes through the eight Channel 2 IM64 commands to the remote 2 device.
All three devices in the scheme perform similarly, ensuring that, so long as one device is able to communicate with
the other two, scheme integrity is maintained.
This Chain topology (normally invoked when a communication link fails) can be used to save cost in a three-
terminal scheme. This is because two legs are cheaper to install than full triangulation implementation. Also if a
suitable communication link is not available between two of the line ends, it may be the only option. If a Chain
topology is used, or one link in a fully triangulated scheme is lost, the operating delay of the teleprotection
commands increases by approximately 7 ms, plus the communications channel signalling delay, due to the
extended path length and additional processing.
3.1.6 PHYSICAL CONNECTION
The protection communications into and out of the products are fibre-optic. Connections are made using BFOC/2.5
connectors (BFOC/2.5 connectors are commonly referred to as “ST” connectors where “ST” is a registered
trademark of AT&T).
According to application, different fibre-optic interfaces are available described in the following table:
Wavelength of light (nm) Fibre type Maximum transmission distance (km)
850 Multi-mode 1
1300 Multi-mode 50
1300 Single-mode 100
1550 Single-mode 150
Connections are made using appropriate fibre-optic cables terminated with BFOC/2.5 connectors. The transmitter
of one device (for example Tx1) is connected to the receiver of another (Rx1 or Rx2 according to the scheme set-
up)
Products can be supplied with the following fibre-optic channel arrangements:
Ch 1 Ch2
850 nm 850 nm
P446SV Chapter 19 - Fibre Teleprotection
P446SV-TM-EN-1 481