Description of Operation
GARD 8000 Distance Relay
RFL Electronics Inc.
9.11
OVERCURRENT ELEMENTS
The GARD 8000 includes a large number of overcurrent elements:
•
3 phase instantaneous overcurrent measuring units (50P-1, 50P-2, 50 P-3)
•
3 ground instantaneous overcurrent measuring units (50G-1, 50G-2, 50G-3)
•
3 negative sequence instantaneous overcurrent measuring units (50Q-1, 50Q-2, 50Q-3)
•
3 phase time overcurrent measuring units (51P-1, 51P-2, 51 P-3)
•
3 ground time overcurrent measuring units (51G-1, 51G-2, 51G-3)
•
3 negative sequence time overcurrent measuring units (51Q-1, 51Q-2, 51Q-3).
9.11.1
INSTANTANEOUS OVERCURRENT ELEMENTS
The instantaneous overcurrent elements are measuring the RMS value of the analog current being fed
to the unit. The unit assert when the RMS value exceeds 1.05 times the set value and resets at the
pickup setting.
The pickup activates the timer that integrates the measured values. The algorithm increases a counter
depending on the input current.
When the RMS falls below the pickup setting, a rapid reset of the integrator occurs. The activation of
the output requires that the pickup current continue throughout the integration time; any reset returns
the integrator to its initial condition so that a new operation initiates the time count from zero.
The ground overcurrent element is operating on a 3I0 quantity calculated from phase RMS values
according to the formula:
C
B
A
I
I
I
I
+
+
=
0
3
The negative sequence overcurrent element is operating on an I2 quantity calculated from phase RMS
values according to the formula:
3
120
1
240
1
2
°
∠
⋅
+
°
∠
⋅
+
=
C
B
A
I
I
I
I
Each instantaneous overcurrent element has an independent timer setting,
All overcurrent units can individually be set directional, forward or reverse. Type of directional
polarization is selectable either from the corresponding directional element or by Zone 2 torque
control.
9.11.2
TIME OVERCURRENT UNITS
The time overcurrent elements are measuring the RMS value of the analog current being fed to the
unit. The unit assert when the RMS value exceeds 1.05 times the set value and resets at 1times the set
value.
The timing function is achieved by integrating the measured values. The integration is made by a
counter that determines the time delay according to the set time curve.
August 1, 2009
9-37
973.334.3100
