Siemens SIPROTEC Manual page 126

Functions
2.5 Distance Protection
In the faulted loop
the voltage U
cation results from:
and
with
U
L3-E
I
L3
I
E
ϕ
U
ϕ
L
ϕ
E
The factors R
The calculation of the phase-to-earth loops does not take place as long as the concerned phase is switched off
(during single-pole dead time) to avoid an incorrect measurement with the now undefined measured values. A
state recognition provides the corresponding blocking signal. A logic block diagram of the phase-to-earth mea-
suring system is shown in Figure 2-46.
Figure 2-46
126
, the phase current I
L3-E L3
= r.m.s.value of the short-circuit voltage
= r.m.s. value of the phase short-circuit current
= r.m.s. value of the earth short-circuit current
= phase angle of the short-circuit voltage
= phase angle of the phase short-circuit current
= phase angle of the earth short-circuit current
/R and X /X are dependent only on the line constants, and no longer on the distance to fault.
E L E L
Logic for a phase-to-earth measuring unit
and the earth current I are measured. The impedance to the fault lo-
E
SIPROTEC, 7SD5, Manual
C53000-G1176-C169-5, Release date 02.2011