ABB RED650 Applications Manual

IEC05000215 V2 EN-US
Figure 51: 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 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
28:
L1 L1
0
1 2 0 f 1 N f
3 U U
3I
Z Z Z 3Z Z ZZ
×
= =
+ + + + +
EQUATION1267 V3 EN-US (Equation 28)
Where:
U
L1
is the phase-to-earth voltage (kV) in the faulty phase before fault
Z
1
is the positive sequence impedance (Ω/phase)
Z
2
is the negative sequence impedance (Ω/phase)
Z
0
is the zero sequence impedance (Ω/phase)
Z
f
is the fault impedance (Ω), often resistive
Z
N
is the earth-return impedance defined as (Z
0
-Z
1
)/3
The high zero-sequence current in solidly earthed networks makes it possible to use
impedance measuring techniques to detect earth faults. 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
GUID-39CAF169-315E-4E3E-9EE6-28CBF624B90E v5
A network is defined as effectively earthed if the earth-fault factor f
e
is less than
1.4. The earth-fault factor is defined according to equation
29.
f
U
U
e
pn
=
max
EQUATION1268 V4 EN-US
(Equation 29)
Section 7 1MRK 505 393-UEN B
Impedance protection
108 Line differential protection RED650 2.2 IEC
Application manual

ABB RED650 Specifications

General

Brand	ABB
Model	RED650
Category	Protection Device
Language	English