ABB REG670 Applications Manual

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
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.
8.3.2.2 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
A
at A side is:
U I p Z I I Rf
A
A L A B
= ⋅ ⋅ + +
( )
⋅
EQUATION1273-IEC-650 V2 EN (Equation 85)
If we divide U
A
by I
A
we get Z present to the IED at A side:
IA + IB
UA
IA IA
ZA = = p ·ZL + ·Rf
EQUATION1274-IEC-650 V1 EN (Equation 86)
The infeed factor (I
A
+I
B
)/I
A
can be very high, 10-20 depending on the differences in
source impedances at local and remote end.
Section 8 1MRK 502 071-UEN -
Impedance protection
216 Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062
Application manual

ABB REG670 Specifications

General

Brand	ABB
Model	REG670
Category	Protection Device
Language	English