RFL Electronics GARD 8000 - Figure 13-30. Fau Lt Detectors

Current Differential Relay
GARD 8000 SYS RFL Electronics
June 20, 2014 13-48 973.334.3100
13.5.1.1 FAULT DETECTORS
The fault detectors described below are combined in OR for each phase and ground to form phase
selective “composite” fault detectors, used to supervise relay operation. For the relay to trip, two
composite fault detectors have to be satisfied as shown in the logic below:
Fault detector of the
local phase in
question
Active fault detector
at remote station
Fault detector of any
other local phase or
ground
Active fault
detector
Figure 13-30. Fault Detectors
13.5.1.1.1 Overcurrent Fault Detector
When the measured current exceeds the user selected threshold the detector is tripped. The
measurement used is the floating measurement, so it does not depend upon zero crossings. The
detector is based upon the magnitude of the current and will thus assert on both positive and negative
current.
There are separate setpoints for the three phases and ground. A small amount of hysteresis is added to
ensure the detection is stable.
13.5.1.1.2 Peak Change Fault Detector
This routine uses the half-cycle current measurements. Each positive half-cycle measurement is
compared to the previous positive half-cycle measurement and each negative half-cycle measurement
is compared to the previous negative half-cycle measurement. Any change that exceeds the user
selected setpoint will assert the detector.