Siemens siprotec 7SA6, Manual

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Functions
6-36
7SA6 Manual
C53000-G1176-C156-2
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.
6.2.2.3 Voltage and Phase-Angle Dependent Current Fault Detection U/I/
ϕ
Function and
Characteristic 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 be-
tween 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 cur-
rents 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 mini-
mum value
Iph>
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 cur-
rent has exceeded a settable minimum value
Iph>
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 volt-
age 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 char-
acteristic curve Figure 6-20. Initially it is shaped like the U/I pick-up characteristic (Fig-
ure 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(I
ϕ
>) which
is cut off by the overcurrent stage I
ϕ
> also comes into effect. The bold dots mark the
Table 6-6 Loop and phase indication for single–phase U/I pick-up;
Phase–earth voltage program in the event of earth faults,
I>> without earth faults (address
1601
)
Pick-up
module Measured
current
Measured
voltage
Earth–fault
detection
Parameter
1Ph FAULTS
Valid
loop
Signalled
Phase(s)
L1
L2
L3 L1
L2
L3 L1–E
L2–E
L3–E yes
yes
yes
any
L1–E
L2–E
L3–E L1, E
L2, E
L3, E
L1
L2
L3 L1
L2
L3 L1–E
L2–E
L3–E no
no
no
any
no pick-up,
no indications
by U
Ph–E
</I>