Voltage And Phase-Angle Dependent Current Fault Detection U/I/J - Siemens siprotec 7SA6 User Manual

6.2.2.3 Voltage and Phase-Angle Dependent Current Fault Detection U/I/ϕ
Function and
Characteristic
7SA6 Manual
C53000-G1176-C133-1
Table 6-6 Loop and phase indication for single–phase
Phase–phase voltage program in the event of earth faults,
phase–phase voltages without earth faults (address )
Pick-up Measured Measured
module current
L1 L1
L2 L2
L3 L3
L1 L1
L2 L2
L3 L3
The pick-up signals of the loop are transformed into phase signals so that faulty
phase(s) can be indicated. If an earth fault has been detected according to 6.2.1, it will
also be indicated.
Phase-angle controlled U/I fault detection can be applied when the U/I characteristic
criteria according to Section 6.2.2.2 can no longer distinguish reliably between load
and short-circuit conditions. This is the case with small source impedances together
with long lines or sequence of lines and intermediate infeed. In the event of a short-
circuit at the end of the line or within the back-up zones of the distance protection the
local measuring voltage will only drop to a small extent so that the phase angle
between current and voltage is required as an additional criterion for fault detection.
U/I/ϕ pick-up is a per phase and per loop pick-up mode. It is crucial for the phase
currents to exceed the pick-up threshold, whereby the pick-up value is dependent on
the size of the loop voltages and the phase angle between current and voltage.
A precondition for measuring the phase–phase angles is that the associated phase
currents as well as the current difference relevant for the loop have exceeded a
minimum value ,SK! that can be set. The angle is determined by the phase–to–
phase voltage and its corresponding current difference.
A precondition for measuring the phase–earth angle is that the associated phase
current has exceeded a settable minimum value ,SK! and that an earth fault
according to Section 6.2.1 has been detected or only phase–to–earth measurements
have been stipulated by setting parameters. The angle is determined by the phase–
to–earth voltage and its corresponding phase current without considering the earth
current.
Pick-up on earth faults is effectively suppressed in networks with non-earthed neutral
points by means of the measures described in Section 6.2.1.
The basic characteristic of the U/I/ϕ pick-up can be seen in the current–voltage
characteristic curve Figure 6-20. Initially it is shaped like the U/I pick-up characteristic
(Figure 6-19).
For angles with large phase angle difference (V and I), i.e. in the short-circuit angle
area above the threshold angle ϕ>, the characteristic between U(I>) and U(Iϕ>) which
Earth–fault
voltage detection
L1–E yes
L2–E yes
L3–E yes
L1–E no
L2–E no
L3–E no
U/I pick-up
;
Parameter Valid
3K )$8/76
loop
L1–E
any L2–E
L3–E
no pick-up,
any no indications
by U
Functions
Signalled
Phase(s)
L1, E
L2, E
L3, E
</I>
Ph–E
6-35