Arcteq Generator Commander, Instruction Manual

Page: 273 / 561

The inrush peak current should also be considered when setting the instant stage. In normal-power
transformers the energizing inrush current may be 10 × I
n
, while the measured current is FFT-filtered
for the fundamental frequency which is used for differential calculation. Typically, the found differential
current is half of the maximum peak current. The instant stage should be 5 × I
n
if the setting should be
according to the theoretical maximum and the margin. Conservative settings should use the 10 ×
I
n
.
The setting value should never cause trips for energizing, but still operate fast during energizing fault
cases. This stage is usually never blocked in applications, and therefore the stage settings should
consider the absolute differential current that is possible in normal operations while keeping the
settings sensitive enough for inrush currents (especially in energiszing cases).
Thus, the setting suggestion for this I
di>Pick-up
stage is 6.0 × I
n
…10 × I
n
for sensitive and conservative
operations respectively.
Finalising the settings
Now the basic settings for the differential stages are applied and the differential protection is ready to
operate. Our example transformer is very small but the formulas presented in this manual can be
applied to transformers of all sizes. If so selected, the relay automatically calculates these settings
(using these same formulas) in the Transformer status monitoring (TRF) module. When everything is set
up correctly in the relay and when the transformer is feeding the load with nominal power, the result
should look like the following example configuration when the example settings and transformer are
used.
Genera Generattor Commander or Commander
Instruction manual
Version: 2.07
© Arcteq Relays Ltd
IM00001 271