Ground Directional (67G/Sg) - GE 350-A9 Instruction Manual

CHAPTER 6: SETPOINTS

Ground directional (67G/SG)

350 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
The Ground Directional element is used to discriminate whether a fault occurs in a forward
or in a reverse direction, and it can be used either individually or as a part of the Ground
Time, or Instantaneous over-current elements. (See the setup for Ground TOC, and Ground
IOC elements.)
The operating current for the Ground directional element is the measured current from the
ground CT input terminals. Depending on the ground CT connection, the measured current
from the CT terminals can be either the current from a zero sequence CT, or the zero
sequence current from a residual CT connection (see figure below).
SOURCE
D8 E8
N I
G
GROUND
GROUND CURRENT INPUT
USED FOR POLARIZING
The polarizing signal for the Ground Directional element is based on the zero sequence
voltage. Depending on the relay's order code, the zero sequence voltage used for the
polarizing voltage, is either calculated, when three-phase voltages are available, or is
measured from the auxiliary voltage input Vx when the three-phase voltages are not
available. For those relays with available phase VTs, the polarizing voltage for the Neutral
directional element is calculated as follows:
Please note, that the phase VT inputs must be connected in Wye.
For those relays with available Vx auxiliary voltage input only, the polarizing voltage for the
Ground directional element is three times the zero sequence voltage measured at the Vx
terminals. The Vx input should be connected to measure 3V
configuration as shown on the figure below.
E5
A
D5
E8 D8
I N
G
GROUND
GROUND CURRENT INPUT
WITH ZERO SEQUENCE CT
S3 PROTECTION
A
B
C
E6 E7
350
B C
PHASE CURRENT
INPUTS
D7
D6
E8 D8
I N
G
GROUND
GROUND CURRENT INPUT
WITH RESIDUAL CONNECTION
898730A1.CDR
from an broken delta VT
0
Eq. 2
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