Directional Transient Ground-Fault Stage; Description - Siemens 7SJ82 Manual

Protection and Automation Functions
6.15 Sensitive Ground-Fault Detection

Directional Transient Ground-Fault Stage

6.15.5
6.15.5.1

Description

Overview
Ground faults occurring in arc-suppression-coil-ground systems often extinguish a short time after the igni-
tion, mostly within a few milliseconds. Such transient occurrences are called transient ground faults. In order
to detect the ground-fault direction, based on these transient occurrences, a special method of measurement
is required that can also capture high frequencies. Conventional methods based on phasor calculations are not
suitable. Even for ground faults lasting for a short time, usually, a high-frequency charging process occurs in
healthy phases. The transient charging process is evaluated by the transient ground-fault method of measure-
ment to determine the ground-fault direction. An integrating method of measurement ensures a high degree
of sensitivity and a positive stability against parasitic signals in the zero-sequence system.
Since permanent ground faults also start with the transient charging process in healthy phases, those errors
will be detected as well.
This process is most suitable for the use in closed loops or meshed systems. Operational, circulating zero-
sequence currents are eliminated and therefore, cannot affect the directional result.
Stage-Control Logic
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Figure 6-130
Blocking the Stage via Binary Input Signal
You can block the stage externally or internally via the binary input signal
blocking, the picked up stage will be reset.
Blocking the Stage in Case of Measuring-Voltage Failure
The stage can be blocked if a measuring-voltage failure occurs. In the event of blocking, the picked up stage
will be reset. The following blocking options are available for the stage:
•
From inside on pickup of the Measuring-voltage failure detection function
•
From an external source via the binary input signal
links in the tripping of the voltage-transformer circuit breaker.
The Blk. by meas.-volt. failure parameter can be set so that measuring-voltage failure detection
blocks the stage or not.
578
Logic Diagram of the Stage Control
>Block stage . In the event of
>Open of the function block Volt.-transf. c. b., which
SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017