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 83 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 83: 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.
Test 2 to Test n: loop back RX+ to TX+ and RX- to TX-. Loop back, one-by-one,
in respective interface in the communication network. Check that the
communication status is OK for each interface point on the local HMI. If no fault is
found, Test 1 and Test 2 should be repeated in reverse order from the remote end.
When loop-back testing is finished, remember to restore the
original terminal numbers. Having the same terminal number at
both ends can cause an unwanted trip. If the terminal was set to Test
mode, check that the local trip is reset before leaving the Test mode
Section 5 1MRK 505 382-UEN B
Communication set-up
100 Communication set-up 670/650 series 2.2
Application Guide
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