Siemens siprotec 7SA6 User Manual

Functions
6-34 7SA6 Manual
C53000-G1176-C133-1
When evaluating phase–phase loops, the sensitivity towards phase–phase faults is
particularly high. In extensive c
ompensated networks this selection is advantageous
because it excludes pick-up as a result of single earth faults on principle. With two-
and three-phase faults it automatically adapts to the prevailing infeed conditions, i.e.
in the weak-infeed operation mode it becomes more current-sensitive, with strong
infeed and high load currents the pick-up threshold will be higher. If only phase–phase
faults are evaluated, the measuring loop is independent of the earth-fault detection,
therefore this procedure is not s
uitable for earthed networks (see Table 6-4).
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
point, however, it requires that the earth–fault criteria according to Section 6.2.1 are
met for all earth faults or double earth faults (see Table 6-5).
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 ,SK!! 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 means (so-called “semi–solid”
earthing). In these cases only earth faults shall be detected by the U/I pick-up. In this
network it is often undesirable that phase–phase short-circuits shall result in a U/I pick-
up.
The measuring loop is independent of the setting SK)$8/76
(address $). Table
6-6 shows the assignment of phase currents, loop voltages and measuring results.
Table 6-4 Loop and phase indication for single–phase U/I pick-up;
Phase–phase voltage program (address )
Pick-up
module
Measured
current
Measured
voltage
Earth fault
detection
Parameter
3K)$8/76
Valid
loop
Signalled
Phase(s)
L1
L2
L3
L1
L2
L3
L1–L2
L2–L3
L3–L1
any any
L1–L2
L2–L3
L3–L1
L1, L2
L2, L3
L1, L3
Table 6-5 Loop and phase indication for single–phase
U/I pick-up;
Phase–phase voltage program in the event of earth faults, phase–phase
voltages without earth faults (address )
Pick-up
module
Measured
current
Measured
voltage
Earth–fault
detection
Parameter
3K$15
Valid
loop
Signalled
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

Siemens siprotec 7SA6 Specifications

General

Brand	Siemens
Model	siprotec 7SA6
Category	Relays
Language	English