ABB RED670 Handbuch Seite 284

Abschnitt 4
IED Anwendung
280
Die Distanzschutzfunktion des IED 670 ist auf die Grundanforderungen
Übertragungsnetzen (starr geerdete Systeme) ausgelegt, kann aber auch auf
Verteilungsnetzen eingesetzt werden.
System earthing
The type of system earthing plays an important roll when designing the protection
system. In the following some hints with respect to distance protection are
highlighted.
Solid earthed networks
In solid earthed systems the transformer neutrals are connected solidly to earth
without any impedance between the transformer neutral and earth.
IEC05000215 V1 DE
Abb. 146: Solidly earthed network.
The earth fault current is as high or even higher than the short-circuit current. The
series impedances determine the magnitude of the earth fault current. The shunt
admittance has very limited influence on the earth fault current. The shunt
admittance may, however, have some marginal influence on the earth fault current
in networks with long transmission lines.
The earth fault current at single line to earth in phase L1 can be calculated as
equation185:
×
3 U
L 1
=
3 I
0
+ + +
Z Z Z 3
1 2 0
EQUATION1267 V1 DE
Where:
UL1 is the phase to earth voltage (kV) in the faulty phase before fault
Z1 is the positive sequence impedance (Ω/phase)
Z2 is the negative sequence impedance (Ω/phase)
Z0 is the zero sequence impedance (Ω/phase)
Zf is the fault impedance (Ω), often resistive
ZN is the earth return impedance defined as (Z0-Z1)/3
U
L 1
=
+ +
Z Z Z Z
f 1 N f
1MRK 505 186-UDE B
xx05000215.vsd
(Gleichung 185)
Applikationshandbuch