5.7.4
Detecting communication faults through loop-back testing
GUID-990AA1AD-3BB4-4A80-AECF-A0E64A4AA996 v1
Loop-back tests are an efficient way to trace the origin of communication faults. Loop-back
testing means that loop-backs are created to the local line differential protection IEDs at
different points in the communication network. Testing encompasses both fibre-optic and
galvanic cable loop-backs depending on their actual positions in the communication network
(see Figure
).
Loop-back testing with X.21 galvanic interface requires special procedures and
equipment. Contact your local ABB representative for more details.
Procedure:
1.
Block the trip circuits.
2.
Set the local and remote terminals to have the same address (
TerminalNo and
RemoteTermNo) on the local HMI under Main menu/Configuration/Communication/
LDCM communication.
3.
Select the synchronization method (GPS or echo).
In most cases, the synchronization method used in loop-back testing
should be the same as is used in actual service. However, in some test
cases, for example with only a single terminal, the external clock should be
set as a master even though it is set as a slave in actual service.
4. Perform the loop-back tests at consecutive points of the communication network.
Number of tests to be performed depends on the actual communication network and the
number of channels.
Figure
shows an example of a loop-back testing set-up.
Transceiver 21-216 is connected to a 64 kbit/s PDH multiplexer (PDH MUX). Transceiver 21-219
is typically connected directly to a 2 Mbit/s SDH multiplexer (SDH MUX), which reduces the
number of interface points for loop-back testing.
IEC08000278-1-en.vsdx
IED
LOCAL
REMOTE
Trans.
21-216
PDH
MUX
SDH
MUX
SDH
MUX
PDH
MUX
Trans.
21-216
IED
Fibre-optic or galvanic loop-back
Test 1
Test 2
Test 3
Test 4
Test 5
Test 6
Test 7
IEC08000278 V1 EN-US
Figure 88: An example of loop-back testing set-up
Test 1: connect RX and TX directly to the actual LDCM with a fibre-optic loop. Check that the
communication status is OK on the local HMI.
If there is more than one LDCM in the local line differential protection IED, the
test must be repeated for each channel.
1MRK 505 382-UEN E
Section 5
Communication set-up
Communication set-up, 670/650 series
89
Application Guide
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