IEC05000216 V2 EN-US
Figure 122: 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. To handle this type phenomena Phase preference logic
function (PPLPHIZ) is needed, which is not common to be used in transmission
applications.
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 element 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.
8.4.2.3 Fault infeed from remote end
SEMOD154453-84 v4
All transmission and most all sub-transmission networks are operated meshed.
Typical for this type of network is that we will have fault infeed from remote end
when fault occurs on the protected line. The fault 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
123, we can draw the equation for the bus voltage V
A
at
left side as:
U I p Z I I Rf
A
A L A B
= ⋅ ⋅ + +
( )
⋅
EQUATION1273-IEC-650 V2 EN-US
(Equation 154)
If we divide V
A
by IA we get Z present to the IED at A side
IA + IB
UA
IA IA
ZA = = p ·ZL + ·Rf
EQUATION1274-IEC-650 V1 EN-US
(Equation 155)
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 239
Application manual
To Next Page
Loading...
