Siemens siprotec 7SA522 User Manual page 207

Assignment to the
Circles and
Zone Pick-up
7SA522 Manual
C53000-G1176-C119-2
F
E
1
Z
I
S1
1
7SA522
6-32a
jX
Z
S2
Z
r
Z
L
F
1
Z
S1
6-32b
Figure 6-32 Polarized MHO circle with quadrature or memorized voltages
The assignment of the loop impedances to the set characteristics of each distance
zones carried out as follows: For each zone the angle between two difference phasors
∆Z and ∆Z
(Figure 6-33) is determined. These phasors result from the difference be-
1 2
tween the two zeniths of the circle diameter and the fault impedance. The zenith Z
corresponds to the set value for the zone under consideration (Z
in Figure 6-30), the zenith k
the difference phasors are:
∆Z
= Z – Z
1 F r
∆Z
= Z – k Z
·
2 F S
In the limiting case, Z
F
between the two difference phasors is 90° (Thales–theorem). Inside the circle the
angle is greater than 90° and outside the circle it is smaller than 90°.
F
2 1
Z
I
L
2
R
6-32c
Z corresponds to the polarizing magnitude. Therefore
·
S
is located on the perimeter of the circle. In this case the angle
Functions
Z
S2
jX
Z
S2
Z
r
Z
L
F
2
Z
S1
and ϕ
as shown
r Line
E
2
R
r
6-59