Ground Distance - GE D30 Instruction Manual

10 APPLICATION OF SETTINGS
ation should also be given to a situation where the load impedance may enter into the relay characteristic for a time longer
than the chosen time delay, which could occur transiently during a system power swing. For this reason the power swing
blocking function should be used.
a) NEUTRAL CURRENT SUPERVISION
The current supervision for the ground distance elements responds to an internally calculated neutral current (3 × I_0). The
setting for this element should be based on twice the zero-sequence line capacitance current or the maximum zero-
sequence unbalance under maximum load conditions. This element should not be used to prevent an output when the load
impedance is inside the distance characteristic on a steady state basis.
b) POLARIZING CURRENT AND NON-HOMOGENEITY CORRECTION ANGLE OF THE QUAD CHARACTERISTIC
An ideal reactance line for single-line-to-ground faults is polarized from the fault current flowing through the fault resistance.
Such a line defines constant reach and could be implemented by the following angle comparator:
The relay could only approximate the unknown fault current by the zero-sequence or the negative-sequence currents mea-
sured at the relaying point. Depending on system parameters, either the zero-sequence or the negative-sequence current
presents better approximation of the fault current angle.
Given the equivalent systems shown in the figure below, the angular difference between the zero-sequence or negative-
sequence currents at the relay, and the fault current can be calculated as follows:
where: A is the local equivalent system
B is the remote equivalent system
L is the line
d is the per-unit (pu) intended reach of the zone (typically 0.7 to 0.9).
Z
0A
Z
1A
GE Multilin
10.2 DISTANCE ELEMENTS (STEPPED DISTANCE SCHEME)

I Z V vs. j
–
I
 
F

angle --------------------- - angle
= =
 
0
I
0_RELAY
I
 
F
 --------------------- -
angle angle
= =
 
2
I
2_RELAY
I
F
dZ (1 – d)Z
0L 0L
I
0
dZ (1 – d)Z
1L 1L
I
2
I
F
Figure 10–1: UNDERSTANDING SYSTEM HOMOGENEITY
D30 Line Distance Protection System

I
F
Z Z Z
+ +
 
0A 0L 0B
------------------------------------------ -
 
 Z
Z 1 d
+ –
0B 0L
Z Z Z
+ +
 
1A 1L 1B
------------------------------------------ -
 
 Z
Z 1 d
+ –
1B 1L
Z
0B
I
2
DEPENDING ON SYSTEM
Z
1B PARAMETERS, I0 OR I2 MAYBE A
BETTER APPROXIMATION OF THE
FAULT CURRENT ANGLE

10.2.2 GROUND DISTANCE

(EQ 10.1)
(EQ 10.2)
(EQ 10.3)
I
0
I
F
842742A1.CDR
10-3
10