P54x/EN AP/La4 Application Notes
(AP) 6-16
MiCOM P543, P544, P545 & P546
AP
P1726ENa
Resistive
Reach
R
Time
Delay
t
Zone Reach
Z
Tilt Angle
Line
Angle
Figure 3 Settings required to apply a quadrilateral zone (Distance option only)
2.3.5.2 Ground characteristic (Distance option only)
In general, the same
setting philosophy would be followed for ground distance protection as
is used for the phase elements. This selection is common to all zones, allowing mho or
quadrilateral selection and generally, the characteristic chosen will match the utility practice.
If applied for long and medium length line protection similarly to LFZP Optimho, LFZR,
SHNB Micromho or SHPM Quadramho models in the ALSTOM Grid range, a mho selection
is recommended. For cable applications, or to set similarly to the MiCOM P441/442/444
models, a quadrilateral selection is recommended.
Quadrilateral ground characteristics are also recommended for all lines shorter than 10 miles
(16 km). This is to ensure that the resistive fault arc coverage is not dependent on mho
circle dynamic expansion, but will be a known set value.
2.3.6 Zone reaches - recommended settings (Distance option only)
The Zo
ne 1
elements of a distance relay should be set to cover as much of the protected line
as possible, allowing instantaneous tripping for as many faults as possible. In most
applications the zone 1 reach (Z1) should not be able to respond to faults beyond the
protected line. For an underreaching application the zone 1 reach must therefore be set to
account for any possible overreaching errors. These errors come from the relay, the VTs
and CTs and inaccurate line impedance data. It is therefore recommended that the reach of
the zone 1 distance elements is restricted to 80% of the protected line impedance (positive
phase sequence line impedance), with zone 2 elements set to cover the final 20% of the line.
The Zone 2
elements should be set to cover the 20% of the line not covered by zone 1.
Allowing for underreaching errors, the zone 2 reach (Z2) should be set in excess of 120% of
the protected line impedance for all fault conditions. Where aided tripping schemes are
used; fast operation of the zone 2 elements is required. It is therefore beneficial to set zone
2 to reach as far as possible, such that faults on the protected line are well within reach. A
constraining requirement is that, where possible, zone 2 does not reach beyond the zone 1
reach of adjacent line protection. For this reason the zone 2 reach should be set to cover
50% of the shortest adjacent line impedance, if possible.
The Zone 3
elements would usually be used to provide overall back-up protection for
adjacent circuits. The zone 3 reach (Z3) is therefore set to approximately 120% of the
combined impedance of the protected line plus the longest adjacent line. A higher apparent
impedance of the adjacent line may need to be allowed where fault current can be fed from
multiple sources or flow via parallel paths.
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