Series Compensated Lines; Overview - GE D30 Instruction Manual

CHAPTER 8: APPLICATION OF SETTINGS

SERIES COMPENSATED LINES

8.2.2.3 Ground distance zone 1
The zone 1 reach must be set so that nominally instantaneous operation does not extend beyond the end of the protected
line. However this can be more complicated than for the phase elements, because of zero sequence mutual induction with
an adjacent parallel line, possibly carried on the same tower, which can be out of service and grounded at multiple points.
A fault beyond 100% of the protected line can cause overreach unless the reach is reduced significantly, sometimes as low
as 65% of the line length. If the line being protected does not have a significant interaction with an adjacent circuit, then
the typical 80% setting can be used. If there is significant mutual coupling between the parallel lines, then the mutual
compensation feature of the ground distance elements can be used instead of a drastic reduction in the reach.
However, even in this case, there is more uncertainty compared with the phase distance elements because the zero-
sequence impedance of the line and thus the zero-sequence-compensating factors can vary significantly due to weather
and other conditions.
8.2.2.4 Ground distance zone 2
To ensure that zone 2 can see 100% of the line, inter-circuit mutual effects must be considered, as they can contribute to a
significant under-reach. Typically this occurs on double circuit lines, when both lines carry the same current. Conduct an
analytical study to determine the appropriate reach setting.
The main purpose of this element is to operate for faults beyond the reach of the local zone 1 element, and therefore a
time delay must be used similar to the phase fault case.
8.2.2.5 Ground distance zone 3
This remote back up function must have a reach that is set to account for any infeed at the remote bus, plus the
impedance of the longest line that terminates on this remote bus. Similar to the phase fault case, a zone 3 element must
be time coordinated with timed clearances on the next section.
8.2.2.6 Ground distance zone 4
As a further contribution to a remote backup philosophy, the reach of this element must be set to account for any infeed at
the remote bus. The time delay must coordinate with other time-delayed protections on the next line. The use of a lens
characteristic or load encroachment element is advantageous when load limits are a problem. To avoid extremely large
reach settings the D30 has the ability to implement any element, so that it is reverse looking. This strategy can be
beneficial if the reduced reach enhances the discrimination between the load and fault conditions. When adopted, this
approach must be implemented at both ends of the protected line.
8.2.2.7 Ground distance zone 5
An additional fifth ground distance zone can be used in special applications. This zone can be the start zone for arming
tripping from all other zones, in both forward and reverse directions of the of protected line. This zone can also be used as
an additional reverse-looking zone for implementation of two reverse-looking zones, thus providing two zone backup
reverse-looking protection. The fifth distance zone can be used as an alarm zone, indicating that load impedance is
approaching the zone characteristic.
8
8.3 Series compensated lines

8.3.1 Overview

It is recommended to apply a combination of distance, ground directional overcurrent, and high-set overcurrent functions
for protection of series compensated lines.
The setting rules described below must take into account variety of system configurations, particularly a status of series
capacitors (in-service, by-passed). Either consider the worst-case topology or, if possible, apply adaptive settings through
the multiple settings groups mechanism.
D30 LINE DISTANCE PROTECTION SYSTEM – INSTRUCTION MANUAL 8-5