Application Guide - NP900 Series
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Figure 3.1.1.2-10 Setting example of zero sequence current transformer application.
Figure 3.1.1.2-11 With current transformer ratio of 200mA/1.5mA earthfault protection
setting 1*I0n will make the function pick-up at 200mA primary current.
3.1.1.3
T
ROUBLESHOOTING
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 currents are connected into the measurement
module, but the order or polarity of one or all phases is
