2.5 Distance Protection
113
7SD5 Manual
C53000-G1176-C169-1
If, apart from the displacement measurement (
3U0> COMP/ISOL.
), there is a fault
detection in more than one phase, this is also rated as a double earth fault. In this way,
double earth faults can be detected even if no or only little earth current flows via the
measuring point.
2.5.1.2
Fault Detection (optional)
Prerequisite
Depending on the ordered version, the 7SD5 distance protection, if configured as the
main or backup protection function, features a range of fault detection modes, from
which the appropriate type for the particular system conditions can be selected. If, ac-
cording to the ordering code, the device only has impedance fault detection (7SD5***-
*****-*
E
** and 7SD5***-*****-*
H
**), or if you have set
Dis. PICKUP
=
Z<
(quadrilat.)
(address
117
) as detection mode, please go to Section 2.5.1.3 „Cal-
culation of the Impedances“. The sections below refer to the ordering codes 7SD5***-
*****-*
D
** and 7SD5***-*****-*
G
**.
Fault detection has to detect a faulty condition in the power system and to initiate all
the necessary procedures for selective clearance of the fault:
• Start of the delay times for the directional and non-directional final stages,
• Determination of the faulted loop(s),
• Enabling of impedance calculation and direction determination,
• Enabling of tripping command,
• Initiation of supplementary functions
• Indication/output of the faulted conductor(s).
The type of fault detection selected with address
117
Dis. PICKUP
=
Z<
(quadrilat.)
works implicitly, i.e the above-mentioned operations are executed
automatically as soon as a fault is detected in one of the distance zones.
Overcurrent Pickup
Overcurrent pickup is a phase-selective pickup procedure. After numeric filtering, the
currents are monitored in each phase for transgression of a set value. A signal is
output for the phase(s) where the set threshold has been exceeded.
For processing the measured values (see Section 2.5.1 „Calculation of the Impedanc-
es“), the phase-selective pickup signals are converted into loop information. This
depends on the earth fault detection and - in earthed power systems - on the param-
eter
1ph FAULTS
according to Table 2-4. For single-phase pickup without earth fault
detection in non-earthed power systems the phase-phase loop is always selected.
The phases that have picked up are signalled. If an earth fault has been detected, it
will also be alarmed.
The pickup will drop out if the signal falls below 95% of the pickup value.
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