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1MRK 506 369-UEN B
8.4.2.7
Line distance protection REL670 2.2 IEC
Application manual
Table 22:
Definition of long lines
Line category
Un
110 kV
Long lines
77 km - 99 km
Very long lines
> 99 km
The possibility to use the binary information from the load encroachment algorithm
improves the possibility to detect high resistive faults at the same time as the
security is improved (risk for unwanted trip due to load encroachment is
eliminated). The possibility to also use the blinder together with the load
encroachment algorithm will considerably increase the security but might also
lower the dependability since the blinder might cut off a larger part of the operating
area of the circle (see to the right of figure 124).
It is recommended to use at least one of the load discrimination functions for long
heavy loaded transmission lines.
Parallel line application with mutual coupling
General
Introduction of parallel lines in the network is increasing due to difficulties to get
necessary area for new lines.
Parallel lines introduce an error in the measurement due to the mutual coupling
between the lines. The lines need not to be of the same voltage in order to
experience mutual coupling, and some coupling exists even for lines that are
separated by 100 meters or more. The reason to the introduced error in measuring
due to mutual coupling is the zero sequence voltage inversion that occurs.
It can be shown from analytical calculations of line impedances that the mutual
impedances for positive and negative sequence are very small and it is a practice to
neglect them.
Mutual coupling effect
The mutual coupling is based on the known induction law, that a current induces a
longitudinal voltage in the parallel circuit.
The induced voltage is:
=
×
U
Z
I
M
IECEQUATION14002 V1 EN-US
Impedance protection
Un
500 kV
350 km - 450 km
> 450 km
Section 8
SEMOD154453-148 v2
SEMOD154453-150 v4
(Equation 156)
243
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