IG-267-EN versión 01; 07/04/2017
23
General Instructions
ekor.rpa
Protection functions
4.3. Directional units
The directional units are combined with the overcurrent
units when taking a decision on tripping. In accordance with
the "torque control" direction setting (Forward or Reverse)
and the result of the direction of the fault, the overcurrent
units finish by tripping or not.
The ekor.rpa-100 model 120 systems have the following
directional units:
• Three phase directional units (3 x 67)
• A neutral directional unit (1 x 67N)
• A sensitive neutral directional unit (1 x 67NS)
4.3.1. Phase directional units
Angular criterion
The phase directional units are units which, using the
angular criterion, determine the direction of each of the
3 phases. The polarisation voltage used for each phase is the
compound voltage corresponding to the other 2 phases.
These units determine direction based on:
• The calibrated settings.
• The phase difference existing between the polarisation
signal and the current signal.
The settings for the phase directional unit are:
• Characteristic phase angle: Characteristic angle
(from - 90.0° to 90.0°). This often corresponds to the
series impedance angle of the lines. Typical values in
distribution: 30° and 45°.
• Minimum phases voltage: Minimum polarisation
voltage (from 0.5 kV to 72.0 kV). Polarisation voltage
value as of which the directional unit considers the
angle reliable, and is capable of determining a direction.
• Indeterminate zone: Indeterminate zone angle (from
0.0° to 90.0°). Setting to establish the indetermination
zone which is close to the zero torque line.
The direction indicated by the units can be Forward, Reverse
or ndef (undefined).
The Forward direction zone is delimited by the following
formula:
The Reverse direction zone will be the opposite of the
Forward zone. In other words, the above formula needs to
be turned around 180° in order to achieve the expression
which delimits the Reverse direction zone.
The directional units will indicate ndef direction if in the
indeterminate zone or polarisation voltage is below the
V
min
setting.
The figure shows an example of operation of the directional
unit of phase A:
1
Reserve
2
Forward
3
Indeterminate zone
4
Zero torque line
5
Maximum torque line
Figure 4.3. Phase A directional unit
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