![background image](http://html1.mh-extra.com/html/abb/relion-670-series/relion-670-series_applications-manual_3052129233.webp)
It can be shown from analytical calculations of line impedances that the mutual impedances
for positive and negative sequence are very small (< 1-2% of the self impedance) and it is a
practice to neglect them.
Classes of networks
From an application point-of-view, there are three types of network configurations (classes)
which must be considered when making the settings for the protection function.
The different network configuration classes are:
1.
Class 1: Parallel line with common positive and zero-sequence network
2.
Class 2: Parallel circuits with common positive but isolated or separated zero-sequence
network
3.
Class 3: Parallel circuits with positive and zero-sequence sources isolated or separated.
One example of class 3 networks could be the mutual coupling between a 400 kV line and rail
road overhead lines. This type of mutual coupling is not so common although it exists and is
not treated any further in this manual.
The most used configuration is class 1 network: Parallel circuit with common positive and zero-
sequence sources. In this type of networks, the parallel transmission lines terminate at
common nodes at both ends.
For each type of network class we can have three different topologies; the parallel line can be
in service, out of service, out of service and earthed in both ends.
The reach of the distance protection zone 1 will be different depending on the operation
condition of the parallel line. It is therefore recommended to use the different setting groups
to handle the cases when the parallel line is in operation and out of service and earthed at both
ends.
Impact on distance protection
Distance relaying of ph-ph and three-phase faults is not influenced by the parallel line. For
protection of phase-to-earth faults, however a measuring error occurs. In principle, this error
appears due to the fact that the parallel line earth-current (I
EP
= 3.I
0P
) induces a voltage I
EP.
Z
0m
/3 in to the fault loop.
The distance relay phase-to-earth units measure:
ph
ph
N
E
Z
U
I
K
I
=
+
×
IECEQUATION14004 V1 EN-US
(Equation 179)
Where:
U
ph
is phase to earth short circuit voltage at the relay location in
the faulted phase
I
ph
is short circuit current in the faulted phase
I
E
earth current of faulty line
K
N
is earth compensation factor for single circuit set at the relay
given by equation
0
1
1
3
N
Z
Z
K
Z
=
-
×
IECEQUATION14005 V1 EN-US
(Equation 180)
1MRK 505 343-UEN B
Section 7
Impedance protection
227
Application manual
Summary of Contents for Relion 670 series
Page 1: ...RELION 670 SERIES Line differential protection RED670 Version 2 1 IEC Application manual...
Page 2: ......
Page 40: ...34...
Page 64: ...58...
Page 150: ...144...
Page 406: ...400...
Page 472: ...466...
Page 494: ...488...
Page 512: ...506...
Page 524: ...518...
Page 604: ...598...
Page 686: ...680...
Page 718: ...712...
Page 722: ...716...
Page 758: ...752...
Page 759: ...753...