tenance
P44x/EN MT/Hb
P444 (MT) 10-
1 MAINTENANCE
1.1 Maintenance Period
It is recommended that products supplied by General Electric receive regular monitoring
after installation. As with all products some deterioration with time is inevitable. In view of
the critical nature of protective relays and their infrequent operation, it is desirable to confirm
that they are operating correctly at regular intervals.
General Electric protective relays are designed for a life in excess of 20 years.
MiCOM P44x distance relays are self-supervising and so require less maintenance than
earlier relay designs. Most problems will result in an alarm so that remedial action can be
taken. However, some periodic tests should be done to ensure that the relay is functioning
correctly and the external wiring is intact.
If a Preventative Maintenance Policy exists within the customer’s organisation then the
recommended product checks should be included in the regular program. Maintenance
periods will depend on many factors, such as:
• the operating environment
• the accessibility of the site
• the amount of available manpower
• the importance of the installation in the power system
• the consequences of a failure
1.2 Maintenance Checks
Although some functionality checks can be performed from a remote location by utilising the
communications capability of the relays, these are predominantly restricted to checking that
the relay is measuring the applied currents and voltages accurately, and checking the circuit
breaker maintenance counters. Therefore it is recommended that maintenance checks be
performed locally (i.e. at the substation itself).
Before carrying out any work on the equipment, the user should be familiar with the
Safety and Installation chapters of this manual.
1.2.1 Alarms
The alarm status LED should first be checked to identify if any alarm conditions exist. If so,
press the read key repeatedly to stop the alarms. Clear the alarms to extinguish the
LED.
1.2.2 Opto-isolators
The opto-isolated inputs can be checked to ensure that the relay responds to their
energisation by repeating the commissioning test detailed in Section P44x/EN CM.
1.2.3 Output Relays
The output relays can be checked to ensure that they operate by repeating the
commissioning test detailed in P44x/EN CM.
1.2.4 Measurement accuracy
If the power system is energised, the values measured by the relay can be compared with
known system values to check that they are in the approximate range that is expected. If
they are, then the analogue/digital conversion and calculations are being performed correctly
by the relay.
Alternatively, the values measured by the relay can be checked against known values
injected into the relay via the test block, if fitted, or injected directly into the relay terminals.
These tests will prove the calibration accuracy is being maintained.
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