Figure. 5.2.1. - 12. With current transformer ratio of 200mA/1.5mA earthfault protection setting 1*I0n will make the function pick-
up at 200mA primary current.
Troubleshooting
It is possible that for some reason the measured currents may not be as expected. For these cases
following checks may be helpful.
Problem
Check / Resolution
Measured current amplitude
in all phases does not
match for what is injected.
Scaling settings may be wrong, check from Measurement, Transformers, Phase CT scaling that
the settings match for what is expected. Also check that the scaling measurement to In is set
accordingly either to “Object In“or CT nominal. If working with CT:s, if possible check the actual
ratings from the CT:s as well, since in some cases the actual CT:s may have been changed
from the original plan for some reason.
Measured current amplitude
does not match for one
measured phase or
calculated I0 is measured
when there should not be
any.
Check wiring connections from injection device or CTs to the IED. NOTE: If working with CTs
which are in energized system extreme caution should be practiced when checking
connections. Opened CT secondary circuit may generate dangerously high voltages. “Buzzing”
sound from connector can indicate open circuit.
Measured current
amplitudes are all ok and
equal but the angles are
strange.
Phase unbalance protection
trips immediately when it is
activated.
Earth fault protection trips
immediately when it is
activated.
Phase currents are connected into the measurement module, but the order or polarity of one or
all phases is incorrect.
Go to Measurement, Phasors and check the current Phasors diagram.
When all is correctly connected the diagram should look as below with symmetric feeding:
In following rows few most common cases are presented.
AQ-F255
Instruction manual
Version: 2.00
© Arcteq Relays Ltd
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