ABB Relion 670 series, Руководство по применению

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instantaneous voltage drop over the capacitor becomes higher than the protective voltage
level in each half-cycle separately, see figure 222 .
Extensive studies at Bonneville Power Administration in USA (
ref. Goldsworthy, D,L “A
Linearized Model for MOV-Protected series capacitors” Paper 86SM357–8 IEEE/PES summer
meeting in Mexico City July 1986) have resulted in 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
p
. The later is defined by equation 388 .
=
MOV
p
NC
U
k
U
EQUATION1910 V1 EN-US
(Equation 388)
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 223: Equivalent impedance of MOV protected capacitor in dependence of
protection factor K
P
Figure 223 presents three typical cases for series capacitor located at line end (case LOC=0%
in figure 221 ).
• 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
).
7.13.3.4 Impact of series compensation on protective IED of adjacent lines
GUID-DA1DBB5B-0AFD-49F4-87C7-0E8AB5006051 v2
Voltage inversion is not characteristic for the buses and IED points closest to the series
compensated line only. It can spread also deeper into the network and this way influences the
1MRK 505 343-UEN B Section 7
Impedance protection
345
Application manual