GE 750 Instruction Manual page 151

S5 Protection
SENSITIVE GND
DIRECTIONAL
NOTE
GE Multilin
d) Sensitive Ground Directional Overcurrent
PATH: SETPOINTS S5 PROTECTION
[ ] SENSTV GND DIRECTN
FUNCTION: Disabled
SENSTV GND DIRECTN
MESSAGE
RELAYS (3-7): -----
SENS GND POLARIZING
MESSAGE
Voltage
SENSTV GND DIRECTN
MESSAGE
MTA: 315° Lead
MIN POLARIZING
MESSAGE
VOLTAGE: 0.05 x VT
The sensitive ground directional feature controls the operation of all sensitive
ground overcurrent elements and allows them to discriminate between forward or
reverse faults. Refer to Phase Directional Overcurrent on page 5–40 for more details
on directional principles. Sensitive ground directional can be either voltage, current,
or dual polarized. The sensitive ground current input is always the operating
current.
When voltage polarized, the polarizing quantity is the zero sequence voltage which
is calculated from the bus input voltages. The VT Connection Type must be Wye in
this case. If the polarizing voltage drops below the
the direction defaults to forward. The following table shows the operating current
and polarizing quantities used for sensitive ground directional control.
Table 5–14: Sensitive Ground Directional Characteristics
Quantity Operating
Current
Sensitive Ground I
sg
On relays with bootware revision 3.00 or newer, the polarizing current is input via
the Ground CT input. Otherwise, the polarizing current is input via a dedicated
polarizing CT input. See Current Inputs on page 3–8 for more details.
When current polarized, the Ground CT Input is used to determine sensitive ground
current direction. The polarizing current comes from a source CT measuring the
current flowing from the ground return into the neutral of a ground fault current
source which is usually a transformer. The direction is Forward when the sensitive
ground current is within ±90° of the polarizing current. Otherwise, the direction is
Reverse. If the polarizing current is less than 5% of CT nominal then the direction
defaults to forward.
Dual polarization provides maximum security and reliability. If the polarizing voltage
magnitude is insufficient then the current polarizing takes control. If the polarizing
current magnitude is insufficient then the voltage polarizing takes control. If neither
voltage nor current polarizing is possible then the direction defaults to forward.
• SENS GND POLARIZING: If sensitive ground directional control with both
voltage and current polarized elements is desired, enter "Dual". With this
setpoint, both polarizing quantities must agree that the operating current is in
the reverse direction for the sensitive ground directional element to operate the
selected output relays. If sensitive ground directional control with only the
voltage polarized element is desired, enter "Voltage". If sensitive ground
directional control with only the current polarized element is desired, enter
"Current".
• SENSTV GND DIRECTN MTA: Enter the maximum torque angle by which the
operating current leads the polarizing voltage. This is the angle of maximum
sensitivity. This setpoint affects voltage polarizing only.
http://www.GEmultilin.com
Feeder Management Relay
SENSITIVE GND... SENSITIVE GND DIRECTIONAL
Range: Disabled,
Alarm, Control
Range: Any combination of 3 to 7
Auxiliary relays
Range: Voltage, Current, Dual
Range: 0 to 359° Lead in steps of 1
Range: 0.00 to 1.25 x VT in steps of
0.01
MIN OPERATING VOLTAGE
Polarizing Voltage
(VT connection = Wye)
–V = –(V + V + V ) / 3
o a b c
750/760
Alarm, Latched
value,
Polarizing Current
I (see note below)
g
5–55