ABB Relion 670 Series Commissioning Manual page 266

Section 13
Commissioning and maintenance of the fault clearing system
13.2.2.7 Measurement of service currents
After a maintenance test it is recommended to measure the service currents and service voltages
recorded by the protection IED. The service values are checked on the local HMI or in PCM600.
Ensure that the correct values and angles between voltages and currents are recorded. Also check
the direction of directional functions such as Distance and directional overcurrent functions.
For transformer differential protection, the achieved differential current value is dependent on the
tap changer position and can vary between less than 1% up to perhaps 10% of rated current. For
line differential functions, the capacitive charging currents can normally be recorded as a
differential current.
The zero-sequence current to ground-fault protection IEDs should be measured. The current
amounts normally very small but normally it is possible to see if the current circuit is "alive".
The neutral-point voltage to an ground-fault protection IED is checked. The voltage is normally 0.1
to 1V secondary. However, voltage can be considerably higher due to harmonics. Normally a CVT
secondary can have around 2.5 - 3% third-harmonic voltage.
13.2.2.8 Restoring
Maintenance is very important to improve the availability of the protection system by detecting
failures before the protection is required to operate. There is however little point in testing
healthy equipment and then putting it back into service with an open terminal, with a removed
fuse or open miniature circuit breaker with an open connection, wrong setting, and so on.
Thus a list should be prepared of all items disturbed during test so that all can be put back into
service quickly and without overlooking something. It should be put back into service item by item
and signed by the responsible engineer.
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Remember to close the circuit directly after the test and tighten the terminal
carefully.
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Line distance protection REL670
Commissioning manual