Measurement Of Service Currents - ABB RET670 Commissioning Manual

Section 14
Commissioning and maintenance of the fault clearing system
14.2.2.7
290
the circuit is not provided with a continuous trip-circuit supervision, it is possible
to check that circuit is really closed when the test-plug handle has been removed by
using a high-ohmic voltmeter and measuring between the plus and the trip output
on the panel. The measurement is then done through the trip coil of the circuit
breaker and therefore the complete trip circuit is checked.
Note that the breaker must be closed.
Please observe that the test system does not provide built-in
security during this test. If the instrument should be set on Amp
instead of Volts, the circuit breaker naturally is tripped, therefore,
great care is necessary.
Trip circuit from trip IEDs to circuit breaker is often supervised by trip-circuit
supervision. It can then be checked that a circuit is healthy by opening tripping
output terminals in the cubicle. When the terminal is opened, an alarm shall be
achieved on the signal system after a delay of some seconds.
Remember to close the circuit directly after the test and tighten the
terminal carefully.

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 earth-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 earth-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.
1MRK 504 165-UEN A
Transformer protection RET670 2.2 IEC
Commissioning manual
SEMOD56528-30 v4