PDH networks are used with 64 kbit/s communication. Proper synchronization of PDH
networks must be available so that hey can be used with protection applications. SDH
networks are used with 2 Mbit/s communication.
SDH networks ≥ 2 Mbit/s
PDH networks ≤ 2 Mbit/s
ATM/IP networks ≥ 622 Mbit/s
Other networks ≥ X Gbit/s
PDH = Plesiochronous Digital Hierarchy
SDH = Synchronous Digital Hierarchy
IEC07000240-1-en.vsdx
PDH/SDH networks are most commonly
used for utility communication
IED
IEC07000240 V1 EN-US
Figure 2:
Telecommunication networks for electric power utilities
2.3
Telecommunication networks with symmetric or fixed
routes
GUID-36D8D02D-E63A-4DFC-83C0-1C37708390AD v1
It is possible to use networks with fixed routes where symmetric time delay is applied, or
networks with fixed route switching where both directions have a symmetric time delay even
after route switching has been performed. In these types of networks, different channel delay
times are automatically compensated for, and echo timing can be used. If a fixed route has
specified asymmetry, this can be compensated for by using the
AsymDelay parameter.
The maximum interruption time for route switching and echo timing (for example when a
communication channel is lost) without affecting the synchronization of internal clocks is 2 s.
The protection function gets blocked for the duration of the interruption. The 2 s time limit is
derived from the stability of the internal clocks. If route switching takes longer than that, the
protection function gets blocked until the internal clocks are re-synchronized. Proper re-
synchronization of the internal clocks takes an additional 15 seconds after the channel is
restored.
From protection point-of-view, route switching interruptions should be < 50 ms (normally
route switching takes < 0.1 ms). The maximum time delay in a telecommunication network can
be set to 40 ms (default delay being 20 ms). In echo timing mode, this time represents round-
trip delay divided by two. If the channel delay is longer than the set value, the protection
function gets blocked.
The recommended value for maximum time delay when using echo timing is 20
ms.
Section 2
1MRK 505 382-UEN E
Telecommunication networks and line differential protection
12
Communication set-up, 670/650 series
Application Guide
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Summary of Contents for Relion 670 series
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