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1MRK 506 369-UEN B
Line distance protection REL670 2.2 IEC
Application manual
construction of a non-linear equivalent circuit with series connected capacitor and
resistor. Their value depends on complete line (fault) current and protection factor
k
. The later is defined by equation 365.
p
U
=
k
MOV
p
U
NC
EQUATION1910 V1 EN-US
Where
U
is the maximum instantaneous voltage expected between the capacitor immediately before
MOV
the MOV has conducted or during operation of the MOV, divaded by √2
U
is the rated voltage in RMS of the series capacitor
NC
I
I
£
1
×
×
Kp
In
Kp
In
R
IEC06000615 V1 EN-US
Figure 207:
Equivalent impedance of MOV protected capacitor in dependence
of protection factor K
Figure
207
presents three typical cases for series capacitor located at line end (case
LOC=0% in figure 205).
•
Series capacitor prevails the scheme as long as the line current remains lower
or equal to its protective current level (I £ k
is in this case reduced for the complete reactance of a series capacitor.
•
50% of capacitor reactance appears in series with resistance, which
corresponds to approximately 36% of capacitor reactance when the line
current equals two times the protective current level (I £ 2· k
information has high importance for setting of distance protection IED reach in
resistive direction, for phase to earth fault measurement as well as for phase to
phase measurement.
•
Series capacitor becomes nearly completely bridged by MOV when the line
current becomes higher than 10-times the protective current level (I £ 10· k
I
).
NC
=
2
I
=
10
×
Kp
In
R
R
en06000615.vsd
P
Section 8
Impedance protection
· I
). Line apparent impedance
p
NC
· I
). This
p
NC
(Equation 365)
·
p
383
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