P341/EN O/B11 Operation Guide
CHAPTER 3 Commissioning and
Page 22/80 Maintenance
MiCOM P341
Compare the values of the secondary phase currents and phase angle with the
relay’s measured values, which can be found in the MEASUREMENTS 1 menu
column.
Note: Under normal load conditions the earth fault function will measure little, if
any, current. It is therefore necessary to simulate a phase to neutral fault.
This can be achieved by temporarily disconnecting one or two of the line
current transformer connections to the relay and shorting the terminals of
these current transformer secondary windings.
If cell [0D02: MEASURE’T SETUP, Local Values] is set to ‘Secondary’, the currents
displayed on the relay LCD or a portable PC connected to the front RS232
communication port should be equal to the applied secondary current. The values
should be within 1% of the applied secondary currents. However, an additional
allowance must be made for the accuracy of the test equipment being used.
If cell [0D02: MEASURE’T SETUP, Local Values] is set to ‘Primary’, the currents
displayed should be equal to the applied secondary current multiplied by the
corresponding current transformer ratio set in ‘CT & VT RATIOS’ menu column (see
Table 10). Again the values should be within 1% of the expected value, plus an
additional allowance for the accuracy of the test equipment being used.
Note: If a P342 or P343 relay is applied with a single dedicated current
transformer for the earth fault function, it may not be possible to check the
relay’s measured values as the neutral current will be almost zero.
7. FINAL CHECKS
The tests are now complete.
Remove all test or temporary shorting leads, etc. If it has been necessary to
disconnect any of the external wiring from the relay in order to perform the wiring
verification tests, it should be ensured that all connections are replaced in accordance
with the relevant external connection or scheme diagram.
Ensure that the relay has been restored to service by checking that cell
[0F0D: COMMISSION TESTS, Test Mode] is set to ‘Disabled’.
If the relay is in a new installation or the circuit breaker has just been maintained, the
circuit breaker maintenance and current counters should be zero. These counters can
be reset using cell [0606: CB CONDITION, Reset All Values]. If the required access
level is not active, the relay will prompt for a password to be entered so that the
setting change can be made.
If the menu language has been changed to allow accurate testing it should be
restored to the customer’s preferred language.
If a MMLG test block is installed, remove the MMLB01 test plug and replace the
MMLG cover so that the protection is put into service.
Ensure that all event records, fault records, disturbance records, alarms and LEDs
have been reset before leaving the relay.
If applicable, replace the secondary front cover on the relay.
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