P54x/EN AP/La4 Application Notes
(AP) 6-46
MiCOM P543, P544, P545 & P546
AP
2.16 Communication between relays
2.16.1 Optical budgets
Whe
n applying any of the P54x range of current differential relays it is important to select the
appropriate protection communications interface. This will depend on the fiber used and
distance between devices. The following table shows the optical budgets of the available
communications interfaces.
From April 2008
850 nm
Multi mode
1300 nm
Multi mode
1300 nm
Single mode
1550 nm
Single mode
Min. transmit output level
(average power)
-19.8 dBm -6 dBm -6 dBm -6 dBm
Receiver sensitivity
(average power)
-25.4 dBm -49 dBm -49 dBm -49 dBm
Optical budget 5.6 dB 43.0 dB 43.0 dB 43.0 dB
Less safety margin (3 dB) 2.6 dB 40.0 dB 40.0 dB 40.0 dB
Typical cable loss 2.6 dB/km 0.8 dB/km 0.4 dB/km 0.3 dB/km
Max. transmission
distance
1 km 50.0 km 100.0 km 130 km
Note: From April 2008, the optical budgets and hence also the maximum
transmission distances of the 1300 nm multi-mode, 1300 nm single-
mode and 1550 nm single-mode fiber interfaces have been increased,
to the values shown in the table above.
The new interface cards are identified by “43dB” marked in the centre of the backplate,
visible from the rear of the relay. These new fiber interfaces are fully backward-compatible
with the original equivalent interface. However, in order to achieve the increased distance,
both/all ends of the P54x scheme would need to use the new interface.
Pre-April 2008 relays will have the original optical budgets and maximum transmission
distances, as shown below.
Pre-April 2008
850 nm
Multi mode
1300 nm
Multi mode
1300 nm
Single mode
1550 nm
Single mode
Min. transmit output level
(average power)
-19.8 dBm -10 dBm -10 dBm -10 dBm
Receiver sensitivity
(average power)
-25.4 dBm -37 dBm -37 dBm -37 dBm
Optical budget 5.6 dB 27.0 dB 27.0 dB 27.0 dB
Less safety margin (3dB) 2.6 dB 24.0 dB 24.0 dB 24.0 dB
Typical cable loss 2.6 dB/km 0.8 dB/km 0.4 dB/km 0.3 dB/km
Max. transmission
distance
1 km 30.0 km 60.0 km 80 km
The total optical budget is given by transmitter output level minus the receiver sensitivity and
will indicate the total allowable losses that can be tolerated between devices. A safety
margin of 3 dB is also included in the above table. This allows for degradation of the fiber as
a result of ageing and any losses in cable joints. The remainder of the losses will come from
the fiber itself. The figures given are typical only and should only be used as a guide.
In general, the 1300 nm and 1550 nm interfaces will be used for direct connections between
relays. The 850 nm would be used where multiplexing equipment is employed.
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