Operation Of Sensitive Earth Fault Element - GE P24DM Technical Manual

P24xM
7.5.9

OPERATION OF SENSITIVE EARTH FAULT ELEMENT

The angular difference between the residual currents on the healthy and faulted feeders allows a directional relay
to be applied whose zero torque line passes between the two currents. The following types of protection elements
may be applied for earth fault detection.
● A suitably sensitive directional earth fault relay having a relay characteristic angle setting (RCA) of zero
degrees, with the possibility of fine adjustment about this threshold.
● A sensitive directional zero sequence wattmetric relay having similar requirements to the above with
respect to the required RCA settings.
Stages 1 and 2 of the sensitive earth fault element of the P24xM relay are settable down to 0.2% of rated current
and would fulfill the requirements of the first method (listed above) and could be applied successfully. However,
many utilities (particularly in central Europe) have standardized on the wattmetric method of earth fault detection,
which is described in the following section.
Zero sequence power measurement, as a derivative of Vo and Io, offers improved relay security against false
operation with any spurious core balance CT output for non earth fault conditions. This is also the case for a
sensitive directional earth fault relay having an adjustable Vo polarizing threshold.
P24xM-TM-EN-2.1
Chapter 6 - Current Protection Functions
129