ABB REL670 2.2 IEC, Руководство по применению

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E
Z
M
I
U
IEC13000253-1-en.vsd
IEC13000253 V1 EN-US
Figure 126: Mutual coupling
Mutual induction on three-phase transmission lines
In case of three phase lines, mutual coupling in the positive and negative sequence
components is relatively weak and can be neglected. These are of the order of 5%
of the related self-impedance for non-transposed and lower than 3% for transposed
lines. The zero-sequence currents are equal and in phase in all the three conductors
of the three-phase line. In this case, the three-phase conductors can be replaced by
a representative single conductor for each parallel line and the mutual coupling
between lines and their earth return wires is then reduced to a single-phase
problem.
E
I
U
IEC13000254-1-en.vsd
O
I
O
I
O
O
O
IEC13000254 V1 EN-US
Figure 127: Mutual coupling of two three-phase lines
0
0
0
3
M
m
Z Z
U
I
=
= ×
IECEQUATION14003 V1 EN-US
(Equation 157)
Where Z
M
is the mutual impedance between two conductors with earth return as
defined above. This zero sequence mutual impedance can be as high as 70% of the
self-zero sequence impedance of a protected line when the parallel lines are
mounted on the same tower. The mutual coupling effect has therefore a strong
impact on the earth-fault relaying.
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.
Section 8
1MRK 506 369-UEN B
Impedance protection
244 Line distance protection REL670 2.2 IEC
Application manual