Functions
2.5 Distance Protection
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011
122
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-to-earth voltage loops if an earth fault has been detected. For
phase-to-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 earthing). In these cases only earth faults must be detected by the U/
I
pickup. In such networks it
is usually even undesirable that phase-to-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 cur-
rents, 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 additional 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.
A precondition for measuring the phase-to-phase angles is that the associated phase currents as well as the
current difference relevant for the loop have exceeded a minimum 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-to-earth angle is that the associated phase current has exceeded a
settable minimum value
Iph>
and that an earth fault 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 cor-
responding phase current without considering the earth current.
Pickup
Module
Measuring
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
Measuring
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
by U
Ph-E
</
I
>
