Ground Directional Overcurrent - GE D30 Instruction Manual

CHAPTER 9: THEORY OF OPERATION
See the Application of Settings chapter for information on setting calculations.

9.3 Ground directional overcurrent

9.3.1 Description
Consider the negative-sequence directional overcurrent element. As shown, the negative-sequence voltage can be low
during internal fault conditions.
In order to ensure operation of the element under such circumstances, the angle comparator uses a polarizing voltage
augmented by the negative-sequence current as per following equations:
Forward-looking element:
Reverse-looking element:
Where ECA = forward ECA angle (maximum torque angle) and Z_offset = offset impedance. The effect of the augmentation
for forward and reverse fault is shown in the previous figure. As long as the offset impedance is not higher than the
negative-sequence line impedance, the element ensures correct and fast fault direction identification for both forward and
reverse faults. The same principle applies to the neutral directional overcurrent element.
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL
Figure 9-6: Offset impedance augmentation
S_pol = -V_2 + I_2 x Z_offset x 1∠ECA
S_op = I_2 x 1∠ECA
S_pol = -V_2 + I_2 x Z_offset x 1∠ECA
S_op = -I_2 x 1∠ECA
GROUND DIRECTIONAL OVERCURRENT
Eq. 9-8
Eq. 9-9
9
9-17