8 ONLOAD CHECKS
Onload checks can only be carried out if there are no restrictions preventing the energisation of the plant,
and the other devices in the group have already been commissioned.
Remove all test leads and temporary shorting links, then replace any external wiring that has been removed
to allow testing.
Warning:
If any external wiring has been disconnected for the commissioning process,
replace it in accordance with the relevant external connection or scheme
diagram.
8.1 CONFIRM CURRENT CONNECTIONS
1. Measure the current transformer secondary values for each input using a multimeter connected in
series with the corresponding current input.
2.
Check that the current transformer polarities are correct by measuring the phase angle between the
current and voltage, either against a phase meter already installed on site and known to be correct or
by determining the direction of power flow by contacting the system control centre.
3. Ensure the current flowing in the neutral circuit of the current transformers is negligible.
4. Compare the values of the secondary phase currents and phase angle with the measured values,
which can be found in the MEASUREMENTS 1 column.
If the Local Values cell is set to Secondary, the values displayed should be equal to the applied secondary
voltage. The values should be within 1% of the applied secondary voltages. However, an additional
allowance must be made for the accuracy of the test equipment being used.
If the Local Values cell is set to Primary, the values displayed should be equal to the applied secondary
voltage multiplied the corresponding voltage transformer ratio set in the CT & VT RATIOS column. The
values should be within 1% of the expected values, plus an additional allowance for the accuracy of the test
equipment being used.
8.2 CONFIRM VOLTAGE CONNECTIONS
1. Using a multimeter, measure the voltage transformer secondary voltages to ensure they are correctly
rated.
2.
Compare the values of the secondary phase voltages with the measured values, which can be found
in the MEASUREMENTS 1 menu column.
Cell in MEASUREMENTS 1 Column Corresponding VT ratio in CT/VT RATIOS column
VXN MAGNITUDE Z1
VXN MAGNITUDE Z2
VXN MAGNITUDE Z3
VXN MAGNITUDE Z4
Main VT Primary / Main VT Sec'y
If the Local Values cell is set to Secondary, the values displayed should be equal to the applied secondary
voltage. The values should be within 1% of the applied secondary voltages. However, an additional
allowance must be made for the accuracy of the test equipment being used.
If the Local Values cell is set to Primary, the values displayed should be equal to the applied secondary
voltage multiplied the corresponding voltage transformer ratio set in the CT & VT RATIOS column. The
Chapter 14 - Commissioning Instructions MiCOM P747
362 P747-TM-EN-1
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