ABB REG670 Applications Manual

IEC05000216 V2 EN
Figure 81: High impedance earthing network
The operation of high impedance earthed networks is different compared to solid
earthed networks, where all major faults have to be cleared very fast. In high
impedance earthed networks, some system operators do not clear single phase-to-
earth faults immediately; they clear the line later when it is more convenient. In case
of cross-country faults, many network operators want to selectively clear one of the
two earth faults.
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. For cross-
country faults and when using phase preference, it is necessary to make sure that the
distance protection is operating in the phase-to-earth loops independently, whenever
possible. See guidelines for setting INReleasePE.
8.2.2.2 Fault infeed from remote end
All transmission and most all 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.
With reference to figure
82, 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 39)
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 40)
1MRK 502 071-UEN - Section 8
Impedance protection
Generator protection REG670 2.2 IEC and Injection equipment REX060, REX061, REX062 191
Application manual

ABB REG670 Specifications

General

Brand	ABB
Model	REG670
Category	Protection Device
Language	English