Siemens siprotec 7SD5, Руководство пользователя

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2 Functions
116
7SD5 Manual
C53000-G1176-C169-1
If the option has been chosen whereby voltage loop selection is dependent on earth-
fault detection, then high sensitivity applies to phase-earth faults and to phase–phase
faults. On principle, this option is independent of the treatment of the network neutral,
however, it requires that the earth–fault criteria according to Section Earth Fault De-
tection are met for all earth faults or double earth faults (see Table 2-7).
Table 2-7 Loops and phase indications for single-phase overcurrent pickup U
I
; Phase-to-
earth-voltages program for earth fault, phase-to-phase voltages without earth
fault
Finally, it is also possible to only evaluate phase-earth voltage loops if an earth fault
has been detected. For phase-phase faults only the overcurrent
Iph>>
will then pick
up. This is advantageous in networks with neutral points that have been earthed low–
resistance, i.e. using earth-fault current limiting measures (so-called semi–solid earth-
ing). In these cases only earth faults must be detected by the U/
I pickup. In such net-
works it is usually even undesirable that phase-phase faults lead to a U/ I pickup.
The measuring loop is independent of the setting
1ph FAULTS
. Table 2-8 shows the
assignment of phase currents, loop voltages and measuring results.
Table 2-8 Loops and phase indications for single-phase overcurrent pickup U I ; Phase-to-
earth-voltages program for earth fault,
I
>> without earth fault
The pickup signals of the loops are converted into phase signals so that the faulted
phase(s) can be indicated. If an earth fault has been detected, it will also be alarmed.
Voltage and Angle-
dependent Current
Pickup U/
I /
ϕ
Phase-angle controlled U/ I pickup can be applied when the U/ I characteristic criteria
can no longer distinguish reliably between load and short-circuit conditions. This is the
case with small source impedances together with long lines or a sequence of lines and
intermediate infeed. Then the local measured voltage will only drop to a small extent
in the event of a short-circuit at the line end or in the back-up range of the distance
protection so that the phase angle between current and voltage is required as an ad-
ditional criterion for fault detection.
The U/ I /
ϕ
pickup is a per phase and per loop pickup mode. It is crucial for the phase
currents to exceed the pickup threshold, with the pickup value being dependent on the
size of the loop voltages and the phase angle between current and voltage.
Pickup
Module
Measur-
ing
Current
Measur-
ing
Voltage
Earth Fault
Detection
Parameter
1ph FAULTS
Valid
Loop
Alarmed
Phase(s)
L1
L2
L3 L1
L2
L3 L1-L2
L2-L3
L3-L1 No
No
No
any
L1-L2
L2-L3
L3-L1 L1, L2
L2, L3
L1, L3
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
Pickup
Module
Measur-
ing
Current
Measur-
ing
Voltage
Earth Fault
Detection
Parameter
1ph FAULTS
Valid
Loop
Alarmed
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 pickup
no alarm
via U
Ph-E
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