Hitachi Relion 670 Series Commissioning Manual page 264

Section 13
Commissioning and maintenance of the fault clearing system
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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1MRK506371-UUS Rev. M
SEMOD56528-36 v2
Line distance protection REL670
Commissioning manual