resistor. Their value depends on complete line (fault) current and protection factor
k
p
. The later is defined by equation
=
MOV
p
NC
U
k
U
EQUATION1910 V1 EN-US
(Equation 59)
Where
U
MOV
is the maximum instantaneous voltage expected between the capacitor immediately before
the MOV has conducted or during operation of the MOV, divaded by √2
U
NC
is the rated voltage in RMS of the series capacitor
en06000615.vsd
R
jX
1
I
£
R
jX
2
I
=
R
jX
10
I
=
Kp
×
In
Kp
×
In
Kp
×
In
IEC06000615 V1 EN-US
Figure 89:
Equivalent impedance of MOV protected capacitor in dependence
of protection factor K
P
presents three typical cases for series capacitor located at line end (case
•
Series capacitor prevails the scheme as long as the line current remains lower
or equal to its protective current level (I
£
k
p
· I
NC
). Line apparent impedance
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
p
· I
NC
). This
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
p
·
I
NC
).
Section 8
1MRK 506 369-UEN B
Impedance protection
180
Line distance protection REL670 2.2 IEC
Application manual
Summary of Contents for REL670 2.2 IEC
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