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5.6 S5 PROTECTION
d) GROUND DIRECTIONAL
PATH: SETPOINTS
S5 PROTECTION
GND DIRECTIONAL
[ENTER] for more
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 OC on page 5–39 for additional details on directional princi-
ples. 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 volt-
ages. The VT Connection Type must be Wye in this case. If the polarizing voltage drops below the
value, the direction defaults to forward. The following table shows the operating current and polarizing quantities used for
ground directional control.
5
Table 5–13: GROUND DIRECTIONAL CHARACTERISTICS
QUANTITY
OPERATING
Ground
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 polar-
izing CT input. See Section 3.2.3: Current Inputs on page 3–8 for more details.
NOTE
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 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 cur-
rent 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 direc-
tional 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 volt-
age. 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
caused by system unbalanced voltages or VT ratio errors. For well-balanced systems and 1% accuracy VTs, this set-
point can be as low as 2% of VT nominal voltage. For systems with high-resistance grounding or floating neutrals, this
setpoint can be as high as 20%. The default value of "0.05 x VT" is appropriate for most solidly grounded systems.
5-50
Courtesy of NationalSwitchgear.com
GND CURRENT
ð
GND DIRECTIONAL
ENTER
ESCAPE
FUNCTION: Disabled
GND DIRECTIONAL
ESCAPE
MESSAGE
RELAYS (3-7): -----
GND POLARIZING
ESCAPE
MESSAGE
Voltage
GND DIRECTIONAL
ESCAPE
MESSAGE
MTA: 315° Lead
MIN POLARIZING
ESCAPE
MESSAGE
VOLTAGE: 0.05 x VT
POLARIZING VOLTAGE
CURRENT
(VT CONNECTION = WYE)
I
–V
= –(V
g
o
a
750/760 Feeder Management Relay
GND DIRECTIONAL
Range: Disabled, Alarm, Latched 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
POLARIZING CURRENT
+ V
+ V
) / 3
I
(see note below)
b
c
pol
5 SETPOINTS
MIN OPERATING VOLTAGE
GE Multilin
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