4.2.6.3
Functionality
The harmonics-based earth-fault protection function HAEFPTOC is used instead
of a traditional earth-fault protection in networks where a fundamental frequency
component of the earth-fault current is low due to compensation.
By default, HAEFPTOC is used as a standalone mode. Substation-wide application
can be achieved using horizontal communication where the detection of a faulty
feeder is done by comparing the harmonics earth-fault current measurements.
The function starts when the harmonics content of the earth-fault current exceeds
the set limit. The operation time characteristic is either definite time (DT) or inverse
definite minimum time (IDMT). If the horizontal communication is used for the
exchange of current values between the protection relays, the function operates
according to the DT characteristic.
The function contains a blocking functionality. It is possible to block function
outputs, timer or the function itself, if desired.
4.2.6.4
Operation principle
The function can be enabled and disabled with the
Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of HAEFPTOC can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
Figure 235: Functional module diagram
Harmonics calculation
This module feeds the measured residual current to the high-pass filter, where the
frequency range is limited to start from two times the fundamental frequency of
the network (for example, in a 50 Hz network the cutoff frequency is 100 Hz), that
is, summing the harmonic components of the network from the second harmonic.
The output of the filter, later referred to as the harmonics current, is fed to the Level
detector and Current comparison modules.
1MRS757644 H
Protection functions
620 series
Technical Manual
461
