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Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection
Determining the Time of the Ground-Fault Ignition
The algorithm uses the evaluation of the instantaneous values of the zero-sequence voltage to verify continu-
ously whether a ground fault occurred. This takes place regardless of whether the set threshold value for V0 is
exceeded. If a ground fault occurred, the measuring window for determining the direction is positioned and
the direction determination is performed. The position of the measuring window is logged via the indication
Pos. measuring window (in FB General). The precise identification of the time T0 at which the ground
fault occurred is decisive for the correct direction determination.
Determination of Direction, Method of Measurement
The active energy of the zero-sequence system is calculated for the direction determination. Once the ground-
fault occurrence has been detected, the active energy will be calculated across approximately 1 cycle
frequency. If the active energy of the zero-sequence system is negative, a forward fault is present; otherwise it
is a backward fault.
Direction Result Message, Pickup
Determining the time of the ground-fault ignition and the direction is always done with maximum sensitivity.
With the parameter V0> threshold value, you define the sensitivity for the indication of the direction and
the pickup of the stage.
If the fundamental-component value of the zero-sequence voltage V0 exceeds the associated threshold value
(V0> threshold value parameter) within 100 ms after detecting the ground-fault ignition, the direction
result will be reported. In this way, high-impedance ground faults are also reported in which the zero-
sequence system values rise only slowly, and, for this reason, the occurrence of the ground fault is detected
noticeably earlier than the exceedance of the parameterized threshold value.
The direction result will be reported to the function via the
block General information. This indication is reported irrespective of the parameterized direction of the func-
tion.
If the determined direction corresponds with the parameterized direction (parameter Directional mode), a
pickup occurs.
Reset of the Algorithm
To allow a new directional measurement, the algorithm needs to be reset. The normal reset takes place when
the fundamental component of the zero-sequence voltage V0 drops below the V0 reset threshold. This reset
threshold is a small device-internal V0 threshold. It is also depending on an operational V0 and is thus a
dynamic threshold. The threshold value is 3.0 V secondary without dynamic influence.
Stabilization against Switching Operations
Switching operations in the system to be protected can cause transient signals in the zero-sequence system.
The stage is stabilized against possible overfunction due to switching operations.
580
(_:2311:302) Ground fault of the function
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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