Effects Of Mutual Coupling On Distance Settings; Effect Of Mutual Coupling On Zone 1 Setting - GE MiCOM P40 Agile Technical Manual

P44x/EN AP/Hb6
(AP) 5-38
A
Z1 Extension (B)
Figure 17: Zone 1 extension scheme
In this scheme, zone 1X is enabled and set to overreach the protected line. A fault on the
line, including one in the end 20% not covered by zone 1, will now result in instantaneous
tripping followed by autoreclosure. Zone 1X has resistive reaches and residual
compensation similar to zone 1. The autorecloser in the relay is used to inhibit tripping from
zone 1X such that on reclosure the relay will operate with Basic scheme logic only, to
coordinate with downstream protection for permanent faults. Therefore, transient faults on
the line will be cleared instantaneously, which will reduce the probability of a transient fault
becoming permanent. The scheme can, however, operate for some faults on an adjacent
line, although this will be followed by autoreclosure with correct protection discrimination.
Increased circuit breaker operations would occur, together with transient loss of supply to a
substation.
The time delays associated with extended zone Z1X are:
Scenario
First fault trip
Fault trip for persistent fault on autoreclose
Table 1: Trip time delays associated with zone 1X
The Zone 1 Extension scheme is selected by setting the Z1X Enable bit in the Zone Status
(distance scheme menu) function links to 1.
Note:

3.1.2.1.3 Effects of Mutual Coupling on Distance Settings

Where overhead lines are connected in parallel or run in close proximity for the whole or part
of their length, mutual coupling exists between the two circuits. The positive and negative
sequence coupling is small and can be neglected. The zero sequence coupling is more
significant and will affect relay measurement during earth faults with parallel line operation.
Zero sequence mutual coupling causes a distance relay to underreach or overreach,
depending on the direction of zero sequence current flow in the parallel line. However, it can
be shown that this underreach or overreach will not affect relay discrimination during parallel
line operation (ie. it is not be possible to overreach for faults beyond the protected line and
neither will it be possible to underreach to such a degree that no zone 1 overlap exists). A
channel-aided scheme will still respond to faults in the protected line and remain secure
during external faults. Some applications exist, however, where the effects of mutual
coupling should be addressed.

Effect of Mutual Coupling on Zone 1 Setting:

For the case shown in Figure 18, where one circuit of a parallel line is out of service and
earthed at both ends, an earth fault at the remote bus may result in incorrect operation of the
zone 1 earth fault elements. It may be desirable to reduce the zone 1 earth loop reach for
this application. This can be achieved using an alternative setting group within the relay, in
Z1A
Z1 < Z1X < Z2
(with Z1 < ZL < Z1X)
To enable the Z1X logic (see section 3.5.2), the DDB: 'Z1X extension' cell must be
linked in the PSL (to an opto input or to reclaim time...)
MiCOM P40 Agile P442, P444
Z1 Extension (A)
ZL
Z1B
or Z1 < Z2 < Z1X
Z1X Time delay
= tZ1
= tZ2
Application Notes
B
P3052ENa