Detecting Communication Faults Through Loop-Back Testing - Hitachi 670 Series Application Manual

Section 5
Communication set-up
Table 32:
LED name
LA
RA
If the line differential protection IED shows a communication fail alarm but LA or RA LED is not lit on
transceiver 21-219, communication interruption stems from the telecommunication network.
5.7.4

Detecting communication faults through loop-back testing

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 89).
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).
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 89
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.
90
LED indicators used for detecting communication faults
Fault indication
Local Alarm. Red LED indicates that transceiver 21-219 has detected a fault condition in the
C37.94 protocol (LOS = Loss Of Signal). The Yellow Alarm bit is set in the outgoing C37.94
protocol.
The red LED is lit when transceiver 21-219 has detected an error. The indication has a memory
function. When the local error is no longer present, the LED blinks until the Reset button is
pressed.
Remote Alarm. Red LED indicates that the remote unit has detected a fault condition, and has
set the Yellow Alarm bit in the C37.94 protocol.
The red LED is lit when the fibre-optic link has detected an error. The indication has a memory
function. When the remote error is no longer present, the LED blinks until the Reset button is
pressed.
Loop-back testing with X.21 galvanic interface requires special procedures and
equipment. Contact your local Hitachi Power grids representative for more details.
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.
shows an example of a loop-back testing set-up.
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1MRK505382-UEN Rev. K
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Communication set-up, 670/650 series
Application Guide