Fault Infeed From Remote End - ABB REG670 Applications Manual

Section 8
Impedance protection
8.3.2.2
216
X is the reactive zero sequence of the source
0
R is the resistive positive sequence of the source
1
X is the reactive positive sequence of the source
1
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
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.

Fault infeed from remote end

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
(
U = I ⋅ ⋅ p Z + I
A L A
A
EQUATION1273-IEC-650 V2 EN
If we divide U by I we get Z present to the IED at A side:
A A
U
I
A
Z = = p ·Z +
A L
I
A
EQUATION1274-IEC-650 V1 EN
The infeed factor (I +I
A B
source impedances at local and remote end.
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
at A side is:
A
)
+ I ⋅ Rf
B
+ I
A B
·R
f
I
A
)/I can be very high, 10-20 depending on the differences in
A
1MRK 502 071-UEN -
(Equation 85)
(Equation 86)
Application manual