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<< Click to Display Table of Contents >> Navigation: Components and parameters > Elements > Shunt capacitor |
The rating of a shunt capacitor can be given in µF (per phase) or in Mvar/kvar (three-phase). The button Appearance is used to switch between the two different input possibilities and to convert between them.
PARAMETERS
Capacitor
Parameter |
Default |
Unit |
Description |
Name |
|
|
Name |
Unom |
1) |
kV |
Nominal voltage |
Q |
0 |
Mvar |
Reactive power |
C 2) |
0 |
μF |
Capacity |
Profile |
Default |
|
Name of the capacitor power profile |
1) Unom of the node
2) Converted from Q and vice versa
Connection
Parameter |
Default |
Unit |
Description |
Star point earthing |
no |
yes/no |
Indicates whether the star point is earthed |
Re |
0 |
Ohm |
Earthing resistance with earthed star point |
Xe |
0 |
Ohm |
Earthing reactance with earthed star point |
External node |
|
|
Node with neutral earth connection |
External node
Possibility to connect the neutral point of the shunt capacitor to the earthing electrode at another node.
Voltage control
Parameter |
Default |
Unit |
Description |
Voltage control on |
off |
on/off |
Indicates whether the voltage control has been switched on or off |
Uoff |
0 |
kV |
Voltage above which the capacitor switches off |
Uon |
0 |
kV |
Voltage under which the capacitor switches on |
Uon < Uoff
Reliability
Parameter |
Default |
Unit |
Description |
Failure frequency |
0 |
per year |
Mean number of occurrences that the capacitor fails (short circuit) |
Repair duration |
0 |
minutes |
Mean duration of repair or replacement |
Maintenance frequency |
0 |
per year |
Mean number of occurrences thet the capacitor is in maintenance |
Maintenance duration |
0 |
minutes |
Mean duration of maintenance |
Maint. cut-off duration |
0 |
minutes |
Mean duration of cancellation of maintenance in case of emergency |
Harmonics
Parameter |
Default |
Unit |
Description |
Frequency |
0 |
|
Harmonic filter frequency |
Quality |
0 |
|
Filter quality |
MODELLING
Load flow and fault analysis
The shunt capacitor is modelled with three capacitors in Wye connection. The rating is given for one capacitor between phase and neutral. The reactive power is always the three-phase power.
For the load flow and the sequential fault analysis, a capacitor is represented as a load with:
Pload = 0
and
Qload = - Qcapacitor
or
Qload = - Unom,capacitor2 × ω C
where:
Qload |
constant X = 100 % |
Qcapacitor |
supplied reactive power at Unom of the shunt capacitor |
Unom,capacitor |
nominal phase to phase voltage of the shunt capacitor |
ω |
Angular frequency ( 2πf ) |
The capacitor is modelled as a constant negative impedance load. This means that the capacitor supplies the nominal reactive power at nominal voltage only. The supplied reactive power depends quadratically on the voltage.
IEC 60909
Capacitors are not taken into consideration in IEC 60909 calculations.
Harmonics
A shunt capacitor can be applied as a harmonic filter. The harmonic filter frequency and filter quality can be specified. The capacitor reactive power is specified on the first tab. The filter resistance and inductance are calculated from the filter input parameters.
The base for the filter parameters is the capacitor reactive power at rated frequency: Qc. The capacitor reactance at the rated frequency (50/60 Hz) is calculated as follows:
where hf is the quotient of the filter frequency and the system frequency.
The induction of the coil at the nominal frequency is calculated as follows:
The filter resistance R is determined from the filter quality factor q. Its value is usually between 20 and 30.
The filter admittance for a frequency with harmonic order h will be: