Table of Contents
Advertisement
Section 12
Commissioning and maintenance of the fault clearing system
12.2.2.7
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.
12.2.2.8
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.
154
© 2017 - 2022 Hitachi Energy. All rights reserved
1MRK 511 409-UUS Rev. K
SEMOD56528-30 v4
SEMOD56528-36 v2
Phasor measurement unit RES670
Commissioning manual
Advertisement
Table of Contents
