GE T60, Instruction Manual

Page: 4 / 796

ADDENDUM
SLG= (VA_LOW & NOT VB_LOW & NOT VC_LOW) OR (NOT VA_LOW & VB_LOW & NOT VC_LOW) OR
(NOT VA_LOW & NOT VB_LOW & VC_LOW)
where
VA_LOW = |V_A + V_0| < 0.98 *VBC/
√
3, similarly for B and C phases
Additionally multi-phase fault is determined if at least 2 phases are below 85% of the nominal:
M-PH= (VA < 0.85pu & VB < 0.85pu) OR (VB < 0.85pu & VC < 0.85pu) OR ( VC< 0.85pu & VA < 0.85pu)
Permission is always granted to phase distance by setting FLGAB, FLGBC and FLGCA flags to logic '1', unless following
condition is satisfied:
PKP_I0 & PKP_I2 & SLG & NOT M-PH,
meaning that if there are negative- and zero-sequence currents present in the fault signal, voltage signatures indicate pres-
ence of the SLG fault and not multi-phase fault. If at least one of these conditions is not satisfied, permission to be contin-
ued granted to all phase distance loop.
But in case this condition is satisfied, angles between I_0 and I_2 are additionally checked to still grant permission to the
phase distance loops, shown below for the ABC rotation.
If abs[ang(I_0)-ang(I_2)+120°] <70°, then FLGAB=1,
If abs[ang(I_0)-ang(I_2)+240°] <70°, then FLGCA=1,
If abs[ang(I_0)-ang(I_2)] <70°, then FLGBC=1,
Phase distance fault type supervision is suppressed during open pole conditions and for delta connected VTs.
Fault type supervision is applied to phase distance zone1 to zone 3 only with an option to disable fault type supervision by
setting phase distance zone 5 Voltage level setting to non-zero-value (regardless zone 5 is enabled or not). G60 and L60
relays are not employing fault type supervision for the phase distance in all zones.
a) FAULT-TYPE CHARACTERISTIC
The fault-type supervision applies to ground and phase elements and is achieved as follows.
For ground elements by checking the angle between
A ground element — I_0 and IA_2
B ground element — I_0 and IB_2
C ground element — I_0 and IC_2
The limit angle of the comparator is not adjustable and equals 50°. The fault-type characteristic is intended to block the
ground distance elements during double-line-to-ground faults. The fault-type supervision is suppressed during open pole
conditions.
Phase elements supervision is applied to block phase distance elements operation during SLG faults. This is done by first
checking if the ground elements fault-type comparator, shown above, does not operate in the corresponding distance loop
and secondly confirming that fault type is matching phase-to-phase or three-phase signatures.