GE D30 Instruction Manual page 431

9 THEORY OF OPERATION
Section (a) of the figure below shows the effect of adaptive reach control for low-current external fault. The reach is reduced
sufficiently to cope with both transient and steady-state overreach. Section (b) shows a high-current external fault. The air
gaps or MOVs conduct majority of the fault current and neither steady-state nor transient overreach takes place. The relay
does not reduce its reach as it is not necessary. Section (c) shows a high-current internal fault. Because of the large cur-
rent, the reach is not reduced and the element responds to this internal fault. Traditional approach would leave this fault out
of the relay reach.
The neutral and negative-sequence directional protection functions of the relay cope with the voltage and/or current inver-
sions by adding appropriate offset to their polarizing signals as explained in the Ground Directional Overcurrent section.
The offset impedance can always be successfully selected to guarantee correct fault direction discrimination regardless of
the degree of compensation and location of the series capacitors and the potential source.
Refer to Chapter 9: Application of Settings for detailed recommendations on settings for series compensation applications.
GE Multilin
X
THE REACH IS
DYNAMICALLY
REDUCED BY
V /abs(I)
L
Figure 9–7: DYNAMIC REACH CONTROL
D30 Line Distance Protection System
9.4 SERIES COMPENSATED LINES
SET REACH (Z )
R
ACTUAL REACH
FOR VERY HIGH
CURRENTS
ACTUAL REACH IS
A FUNCTION OF
CURRENT
MAGNITUDE
ACTUAL REACH
FOR VERY SMALL
CURRENTS
R
837729A1.CDR
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