ABB REL670 2.2 IEC, Руководство по применению

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IEC05000215 V2 EN-US
Figure 133: 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 phase-to-earth in phase L1 can be calculated as
equation
184 :
L1 L1
0
1 2 0 f 1 N f
3 U U
3I
Z Z Z 3Z Z Z Z
×
= =
+ + + + +
EQUATION1267 V3 EN-US
(Equation 184)
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
The voltage on the healthy phases is generally lower than 140% of the nominal
phase-to-earth voltage. This corresponds to about 80% of the nominal phase-to-
phase voltage.
The high zero sequence current in solid earthed networks makes it possible to use
impedance measuring technique to detect earth fault. However, distance protection
has limited possibilities to detect high resistance faults and should therefore always
be complemented with other protection function(s) that can carry out the fault
clearance in those cases.
Effectively earthed networks
SEMOD154680-40 v4
A network is defined as effectively earthed if the earth fault factor fe is less than
1.4. The earth fault factor is defined according to equation
185 .
Section 8
1MRK 506 369-UEN B
Impedance protection
262 Line distance protection REL670 2.2 IEC
Application manual