Table of Contents
Advertisement
70
3 zone impedance protection (Z(n)RW)
Z
:
phase conductor impedance
1
R
:
fault resistance
F
a)
I
U
U
L2
L1
)LJXUH (TXLYDOHQW FLUFXLW IRU PHDVXULQJ SKDVHWRSKDVH IDXOW
The total impedance, according to figure 36, is equal to:
= 2 ⋅
Z
Z
R
+
loop
1
F
/RDG LPSHGDQFH OLPLWDWLRQ
Check the maximum permissible resistive reach for any zone to ensure that there is a
sufficient setting margin between the relay boundary and the minimum load impedance.
6HWWLQJ RI PLQLPXP RSHUDWLQJ FXUUHQW
Minimum operating fault current IMinOp defines the sensitivity of the distance protec-
tion as built in the terminal. Default setting value, which is 20% of basic terminal cur-
rent, proved in practice as the optimum value for the most of applications.
Sometimes it is necessary to increase the sensitivity by reducing the minimum operat-
ing current down to 10% of terminal basic current. This happens especially in cases,
when the terminal serves as a remote back-up protection on series of very long trans-
mission lines.
b)
F
L1
U
L2
&KDSWHU
/LQH LPSHGDQFH
I
Z
1
L1,2
R
F
Z
L1,2
1
en02000644.vsd
(Equation 27)
Advertisement
Table of Contents
