Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
9.1.5
DISTANCE CHARACTERISTIC
The Mho and Quadrilateral characteristics can be used independently, or combined. There are four
setting choices available; Mho only, Quadrilateral only, Mho AND Quadrilateral, and Mho OR
Quadrilateral. These selections are done independently for phase-to-ground elements and phase-to-
phase elements but are common to all zones.
9.1.6
DISTANCE ELEMENTS OPERATIONAL LOGIC
The distance elements AG, BG, CG, AB, BC and CA for Zone to Zone 4 are combined with a number
of other supervisory elements to produce an output:
•
Current supervision elements
•
Phase selector
•
Open pole detector
•
Fuse fail (loss-of-potential) detector
•
Load encroachment
Phase to ground fault element logic is shown in the Figure below. Single-phase to ground measuring
elements in the leading phase are not allowed to operate for two-phase to ground faults as they will
overreach. However, the lagging phase can be allowed to operate as it will be underreaching. This is
enabled by the setting “Lagging phase for PH-PH-G faults”. In either case, two-phase-to-ground faults
will also be measured by the phase-to-phase impedance unit.
The ‘pole-open’ release of the single phase to ground element is used for single pole trip applications
when the phase selector is not operational during the open pole interval.
ZONE n AG (C_n_AG) DISTANCE CHARACTERISTIC
FORWARD AG ELEMENTS SUPERVISION (IDA)
AG FAULT (AG)
CAG FAULT (CAG)
PHASE LAG ENABLE
SETTING
ZONE n (n_AG) AG ELEMENT PICKUP
POLE B OPEN (PB_A)
POLE C OPEN (PC_A)
FUSE FAILURE BLOCKING (BLQ_FF)
LOAD ENCROACHMENT ACTIVATION (DEL)
Figure 9-8. AG Distance Element Operational Logic
August 1, 2009
9-12
973.334.3100
