Direction Determination and Pulse Counting
When the RMS value of 3I0 exceeds the set threshold value (signal no. 3 in Figure 6-116), the direction deter-
mination process is started and is continuously carried out until the function resets. At first, the current pulse
(current peak) detection takes place. If a current pulse is detected, the direction determination for this pulse is
carried out.
The direction is determined by calculating the active zero-sequence energy of the current pulse. The active
zero-sequence energy of the pulse is compared to internal threshold values resulting in the directional deci-
sion forward, reverse, or non-directional. During the ongoing intermittent ground fault, the direc-
tional results for all current pulses are counted.
Directional Mode and Directional Pulse Counter Criterion
The parameter Directional mode defines whether the function operates in forward or in reverse direc-
tion. The pulses in the specified direction are counted. If the pulse counter reaches the threshold value set in
the parameter No. of pulses for operate, the signal
Pulse no. reached
is issued. Depending on
the operating mode (Counter or Integrator and counter) of the function, the signal can immediately
cause the operate of the function (Counter mode) or it is processed as directional release criteria (Inte-
grator and counter operating mode). Refer to the further description in the following sections.
The directional pulse counter is reset when a different direction than the set Directional mode is detected.
An undefined direction result does not reset the counter.
Operating Mode
2 different functional operating modes are available: Counter and Integrator and counter. You can
select the different operating modes using the parameter Operating mode.
•
Operating mode Counter:
Many ground-current pulses of intermittent ground faults can result in a damage of the protected object.
In this mode, the criterion for operate is only the number of directional current pulses. This is similar to
the SIPROTEC 4 implementation.
•
Operating mode Integrator and counter:
An intermittent ground fault can result in thermal stress on the protected object. The magnitude and the
duration of the ground-current pulses are decisive for the thermal stress. In order to calculate the thermal
stress, the stage sums up the duration of the stabilized pickups with an integrator. If the integration value
reaches the threshold value, one criterion for the operate is fulfilled. The 2nd criterion for the operate is
the ground-fault direction. The ground-fault direction is determined by counting the directional ground-
current pulses.
Protection and Automation Functions
6.14 Directional Intermittent Ground-Fault Protection
554 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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