IG-267-EN versión 01; 07/04/2017
22
Protection functions General Instructions
ekor.rpa
Basically, the diagram shows that, whenever a magnitude
measured in real-time (Ix) exceeds the setpoint value (l
pick up
setting), a time counter counts down (counter: f (curve,
index, time), tripping when completely expired.
If the measured magnitude (Ix) drops below the setpoint
(I
pick up
) during timing, the unit and the meter are reset and
the unit remains idle.
All the units generate the following signalling:
• Pick-up: Activated when the measured magnitude (Ix)
exceeds a setpoint (I
pick up
setting) and disabled when the
metering value drops below the setpoint.
• Temporize: Activated when the time counter reaches
its end, and disabled when the metering value drops
below the setpoint.
• Trip: Activated when the temporize signal is activated,
and disabled when the metering value drops below the
setpoint.
Moreover, the overcurrent units can be blocked by the
maximum current blocking and second harmonic
blocking units detailed in the following sections.
Moreover, the overcurrent units can be blocked in three
different ways:
• Unit block: Blocks the unit, preventing start-up while
this input remains active.
• Timing Block: Freezes the time counter value while this
input is active.
• Trip Block: Allows the unit to advance, and blocks it
before the trip output.
4.2. Ultra-sensitive earth
This functionality is available in both directional and non-
directional ekor.rpa and corresponds to a particular case of
overcurrent detection for phase-to-earth faults. Primarily
used in networks with isolated neutral, resonant earthed
neutral or on highly resistive soils, where the phase-to-
earth fault current has a very low value.
The current flowing to earth is detected using a toroidal-
core current transformer which covers the three phases.
In this way, the metering is independent from the phase
current, thus avoiding errors in the phase metering sensors.
Using this type of toroidal-core means the measured
neutral currents due to unbalanced phases are reliable in
very low primary amp values. For this type of configuration,
the unit allows a minimum trip setting of 0.3 primary amps
in its Sensitive Neutral channel.
1
Voltage and current sensors
2
Zero-sequence transformers
Figure 4.2. Current sensors
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