Where:
U
max
is the highest fundamental frequency voltage on one of the healthy phases at single
phase-to-earth fault.
U
pn
is the phase-to-earth fundamental frequency voltage before fault.
Another definition for effectively earthed network is when the following relationships between
the symmetrical components of the network impedances are valid, see equations
0
1
X
3 X
< ×
EQUATION2122 V1 EN-US
(Equation 359)
0
1
R
R
£
EQUATION2123 V1 EN-US
(Equation 360)
Where
R
0
is the resistive zero sequence of the source
X
0
is the reactive zero sequence of the source
R
1
is the resistive positive sequence of the source
X
1
is the reactive positive sequence of the source
The magnitude of the earth-fault current in effectively earthed networks is high enough for
impedance measuring elements to detect earth faults. However, in the same way as for solidly
earthed networks, 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 this case.
High impedance earthed networks
GUID-123D2D9D-8055-4A2F-9CC2-6EAE0C9F905B v1
In this type of network, it is mostly not possible to use distance protection for detection and
clearance of earth faults. The low magnitude of the earth-fault current might not give start of
the zero-sequence measurement elements or the sensitivity will be too low for acceptance. For
this reason a separate high sensitive earth-fault protection is necessary to carry out the fault
clearance for single phase-to-earth fault.
ZMFCPDIS is not designed for high impedance earthed networks. We recommend using the
ZMQPDIS distance function instead, possibly together with the Phase preference logic
(PPLPHIZ).
7.13.2.2
Fault infeed from remote end
GUID-DDFE8B5C-A064-4956-B8BB-49DEAC38558E v2
All transmission and most sub-transmission networks are operated meshed. Typical for this
type of network is that fault infeed from remote end will happen when fault occurs on the
protected line. The fault current infeed will enlarge the fault impedance seen by the distance
protection. This effect is very important to keep in mind when both planning the protection
system and making the settings.
The equation for the bus voltage U
A
at A side is:
U
I
p Z
I
I
Rf
A
A
L
A
B
=
⋅
⋅
+
+
(
)
⋅
EQUATION1273-IEC-650 V2 EN-US
(Equation 361)
Section 7
1MRK 505 343-UEN B
Impedance protection
326
Application manual
Содержание Relion 670 series
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