Protection Functions
188 PRS-7367
3.38 Wattmetric sensitive earth-fault protection SEF
3.38.1 Overview
The function measures the earth-fault power and gives an operating signal when the residual
current, residual voltage and earth-fault power exceed the pickup settings value and the angle
between the residual current and residual voltage is inside the set operating region, that is,
forward or backward region. The operating time characteristic can be selected to be either definite
time (DT) or a special wattmetric-type inverse definite minimum type (wattmetric type IDMT).
The wattmetric earth-fault protection is very sensitive to current transformer errors and it is
recommended that a core balance CT is used for measuring the residual current (the core balance
CT should be check the pole before used).
The function contains a blocking functionality. It is possible to block function outputs, timers or the
function itself, if desired.
3.38.1.1 Function block
The function block of the protection is as below.
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