Technical Guide P92x/EN CM/E11
Commissioning Guide
MiCOM P921-P922-P923 Page 23/28
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6. ON-LOAD CHECKS - VOLTAGE INPUT CONNECTIONS
The following on-load measuring checks ensure the external wiring to the voltage
inputs is correct but can only be carried out if there are no restrictions preventing the
energisation of the plant being protected.
REMOVE ALL TEST LEADS, TEMPORARY SHORTING LEADS, ETC. AND
REPLACE ANY EXTERNAL WIRING THAT HAS BEEN REMOVED TO ALLOW
TESTING.
IF IT HAS BEEN NECESSARY TO DISCONNECT ANY OF THE EXTERNAL
WIRING FROM THE RELAY IN ORDER TO PERFORM ANY OF THE FOREGOING
TESTS, IT SHOULD BE ENSURED THAT ALL CONNECTIONS ARE REPLACED IN
ACCORDANCE WITH THE RELEVANT EXTERNAL CONNECTION OR SCHEME
DIAGRAM.
USING A MULTIMETER, MEASURE THE VOLTAGE TRANSFORMER
SECONDARY VOLTAGES TO ENSURE THEY ARE CORRECTLY RATED. CHECK
THAT THE SYSTEM PHASE ORDER IS CORRECT USING A PHASE METER.
COMPARE THE VALUES OF THE SECONDARY PHASE VOLTAGES WITH THE
RELAY'S MEASURED VALUES, WHICH CAN BE FOUND IN THE
MEASUREMENTS MENU.
The values measured by the MiCOM relay should be within 1% of the applied
primary voltages. However, an additional allowance must be made for the accuracy
of the test equipment being used.
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