GE T60, Instruction Manual

Page: 3 / 796

ADDENDUM
This addendum outlines items not included in the instruction manual for the T60.
PHASE DISTANCE FAULT TYPE CHARACTERISTICS
Phase distance fault type characteristics were slightly changed between minor version 7.21 and 7.24 firmware releases to
allow phase distance operation during some unusual cases, where spurious I_0 can be present during fault. This adden-
dum explains the difference in the firmware implementation for the following minor releases.
a) FIRMWARE 7.21
For phase distance following fault-type characteristic are applied.
FLGAB= ~(AG OR BG) OR I0< max(0.02 pu, I2/16, I1/16)
FLGBC= ~(BG OR CG) OR I0< max(0.02 pu, I2/16, I1/16)
FLGCA= ~(CG OR AG) OR I0< max(0.02 pu, I2/16, I1/16)
where
"~" means inverse operation
I0 is the zero sequence current magnitude
I2 is the negative sequence current magnitude
AG, BG, CG are ground distance single-line-to-ground (SLG) fault-type signatures, explained in the Fault-Type Characteris-
tic section later
This means that fault-type characteristic for the phase distance is confirmed, if there is no SLG fault in the corresponding
loop or if zero-sequence current is relatively small, which is true for phase-to-phase or three-phase fault. Phase distance
fault type supervision is suppressed during open pole conditions.
b) FIRMWARE 7.24 AND 7.25
Version 7.24 added additional angle between I_1 and I_2 along with I_1 and I_2 level detectors. I_1 phasor is obtained by
subtracting pre-fault positive sequence current I1mem from the fault positive sequence current.
θ 12=ang(I1)-ang(I2), limit angle 45°
PKP_I0= I0>max(0.02 pu, I2/16, I1/16)
PKP_I2= I2>max(0.02 pu, I0/16, I1/16)
PKP_I1= abs(I1(k)- I1mem )>0.05pu
FLG 3P= PKP_I1 & NOT PKP_I2
For the ABC, rotation phase distance fault type characteristics applied are as follows:
FLGAB= ~(FLG5A OR FLG5B) OR [abs( θ 12+60°)<45° AND (PKP_I0 OR PKP_I2)] OR PS_3P
FLGBC= ~(FLG5B OR FLG5C) OR [abs( θ 12+180°)<45° AND (PKP_I0 OR PKP_I2)] OR PS_3P
FLGCA= ~(FLG5C OR FLG5A) OR [abs( θ 12+300°)<45° AND (PKP_I0 OR PKP_I2)] OR PS_3P
This means that the first check is if the ground elements fault-type comparator, explained in the Fault-Type Characteristic
section later), does not operate in the corresponding distance loop. Second, the angle between (I_1 - I_1mem) and I_2 is
checked to be within 45° in the corresponding phase distance loop. I_1mem is the pre-fault positive sequence current,
which is updated with the actual I_1 phasor of two cycles before fault. Upon 50DD assertion, I_1mem stops updating and is
sealed-in for 500 ms. In case any phase distance zone is picked-up after this 500 ms seal-in timer expires, I_1mem contin-
ues to be held until either all phase distance zones drop out or for three seconds after any zone is still picked up. After that,
I_1mem is updated again. Lastly, condition for the three-phase fault is checked. Phase distance fault type supervision is
suppressed during open pole conditions.
c) FIRMWARE 7.26
In order to improve phase distance fault type supervision especially during complex faults and to give user flexibility to dis-
able fault type supervision, following is applicable in this release.
Fault type supervision is designed to ensure dependability of the phase distance operation. It uses first voltages and then
currents to ensure giving permission to phase distance for any fault. First the SLG fault type is determined by detecting one
phase voltage depressed while two others are not by using the following equation.