GE 750 Instruction Manual page 147

S5 Protection
GROUND
DIRECTIONAL
NOTE
GE Multilin
d) Ground Directional Overcurrent
PATH: SETPOINTS S5 PROTECTION
[ ] GND DIRECTIONAL
FUNCTION: Disabled
GND DIRECTIONAL
MESSAGE
RELAYS (3-7): -----
GND POLARIZING
MESSAGE
Voltage
GND DIRECTIONAL
MESSAGE
MTA: 315° Lead
MIN POLARIZING
MESSAGE
VOLTAGE: 0.05 x VT
The Ground Directional feature controls operation of all ground overcurrent
elements and allows them to discriminate between forward or reverse faults. Refer
to Phase Directional Overcurrent on page 5–40 for additional details on directional
principles. Ground directional can be either voltage, current, or dual polarized. The
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 ground directional control.
Table 5–13: Ground Directional Characteristics
Quantity Operating
Current
Ground I
g
On relays with bootware revision 3.00 or newer, the ground directional element may
only be voltage polarized since these relays do not have a polarizing current 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 'Polarizing CT Input' is used to determine 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 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.
• GND POLARIZING: If ground directional control with both voltage and current
polarized elements is desired, enter "Dual". If ground directional control with
only the voltage polarized element is desired, enter "Voltage". If ground
directional control with only the current polarized element is desired, enter
"Current".
• GND DIRECTIONAL 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.
• MIN POLARIZING VOLTAGE: This setpoint affects the voltage element only.
As the system zero sequence voltage is used as the polarizing voltage for this
element, a minimum level of voltage must be selected to prevent operation
http://www.GEmultilin.com
Feeder Management Relay
GROUND CURRENT
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
GROUND DIRECTIONAL
Alarm, Latched
value,
Polarizing Current
I (see note below)
pol
5–51