Table 22: Definition of long lines
Line category
Un Un
110 kV 500 kV
Long lines 77 km - 99 km 350 km - 450 km
Very long lines > 99 km > 450 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.
8.4.2.7 Parallel line application with mutual coupling
SEMOD154453-148 v2
General
SEMOD154453-150 v4
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:
IECEQUATION14002 V1 EN-US (Equation 156)
1MRK 506 369-UEN B Section 8
Impedance protection
Line distance protection REL670 2.2 IEC 243
Application manual
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