Advanced Distance Zone Settings; Distance Zone Sensitivities - GE MiCOM P40 Technical Manual

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The Delta Directional technique needs the changes in voltage and current to exceed the preset thresholds, in order
to determine forward and reverse decisions. If these thresholds are not exceeded, but a potential fault is detected,
the Distance protection reverts to a conventional directional technique with memory polarization of the voltage.
If you don't want to use the Delta directional technique, set Dir. Status in the DISTANCE SETUP column to
Disabled in which case memory polarization is used.
4.6.2

ADVANCED DISTANCE ZONE SETTINGS

The Setting Mode is set in the DISTANCE SETUP column. There are two possible modes; simple and advanced.
If set to Simple, you need only to enter the line parameters such as length, impedances and residual
compensation found in the LINE PARAMETERS column. You set the reach in terms of percentage of the protected
line.
We recommend the Advanced setting for networks where the protected and adjacent lines are of dissimilar
construction, requiring independent zone characteristic angles and residual compensation. In this setting mode all
individual distance ohmic reach and residual compensation settings and operating current thresholds per each
zone are accessible.
If you use the advanced setting mode, you also need to set the minimum current sensitivity for each zone (Zn
Sensit. Iph>n, and Zn Sensit. Ignd>n).
The current sensitivity setting for each zone is used to set the minimum current that must flow in each of the
faulted phases before a trip can occur. For example, if a phase A-B line fault is present, the protection must
measure both currents Ia and Ib above the minimum set sensitivity.
The default setting is 7.5% In for Zones 1 and 2, and 5% In for other zones, ensuring that distance element
operation is not constrained, right through to an SIR ratio of 60.
When quadrilateral characteristics are used, you can set the tilt angle of the impedance reach lines.
In Advanced setting mode, the impedance reach lines of the quadrilateral characteristics are fixed, but not as
horizontal reactance lines. To account for phase angle tolerances in the current and voltage transformers, etc., the
lines are tilted downwards at a droop of -3°.
In Advanced setting mode, the tilt of the top lines can be changed from these values.
4.6.3

DISTANCE ZONE SENSITIVITIES

In the Simple Setting Mode a minimum current sensitivity applies but the value is automatically calculated and
applied based on the data entered in the 'Simple' settings fields. The criteria used to calculate the setting value are
needed for a minimum value of current flowing in the faulted loop and for the Zone reach point voltage. For Zones
other than 1 or 2, the minimum current must be greater than 5% of the rated current and the minimum voltage at
the Zone reach point must be 0.25V. The current equating to the reach point criteria can be expressed as 0.25/
Zone reach and the sensitivity can be expressed as:
Sensitivity = max (5%In, (0.25/Zone reach))
Zones 1 and 2 are set less sensitive than the reverse Zone 4. This ensures stability of the protection in either an
overreaching or a blocking scheme. For Zones 1 and 2, the same criteria are applied as for the other Zones. Also a
minimum sensitivity criterion is applied, depending on the Zone 4 sensitivity. The sensitivity must exceed 1.5 x Zone
4 sensitivity and can be expressed as:-
Sensitivity (Z1, Z2) = max (5%In, (0.25/Zone reach), (1.5 x Zone 4 sensitivity))
Or
Sensitivity (Z1, Z2) = max (5%In, (0.25/Zone reach), (1.5 x (0.25/Zone 4 reach)))
The dependency on the Zone 4 element always applies, even if Zone 4 is disabled.
The default reach setting for Zones 1, 2, and 4 are 80%, 120%, and 150% respectively. For these settings the zone-
dependent terms can be reduced to:
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Chapter 7 - Distance Protection
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