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A line is the model for a three-phase (high-voltage) line or another connection between two nodes, of which the type data is not known but the electrical properties.
A connection consists of one or more serial connection parts, where a description can be specified. A connection part has three values for Inom. The choice can be made in the general calculation options.
With a connection, the nominal voltages of both nodes must be the same.
PARAMETERS
General
In this screen, the positions of the switches on both sides of the connection can be changed.
Parameter |
Description |
Name |
Name of the connection |
Resistance symbol |
Resistance symbol in the scheme |
Subnet border |
Division of parts of the network which are fed through different transformers or sources |
From-node |
Name of the node from which the cable is connected |
To-node |
Name of the node to which the cable is connected |
A line runs from a From-node towards a To-node. The From-node and To-node can be exchanged using the button: <>.
A line is composed of one or several line parts. For each line part a name can be given. Several line parts can be added with the buttons Add (add to the bottom of the list) or Insert (insert before the current connection part in the list). With the button Remove the line part can be removed from the list.
Line parts
Parameter |
Default |
Unit |
Description |
Rac |
0 |
Ohm |
Operational A.C. resistance, at specified temperature |
TR |
30 |
degrees C |
Temperature corresponding to the value of R |
X |
0 |
Ohm |
Operational reactance |
C |
0 |
μF |
Operational capacity |
R0 |
0 |
Ohm |
Zero sequence resistance |
X0 |
0 |
Ohm |
Zero sequence reactance |
C0 |
0 |
μF |
Zero sequence capacity |
Length |
0 |
m |
Length (for harmonics calculation) |
Inom1 |
0 |
A |
Nominal current |
Inom2 |
0 |
A |
Alternative nominal current |
Inom3 |
0 |
A |
Alternative nominal current |
Ik 1s |
0 |
kA |
Admissible short-circuit current for 1 second |
TIk(1s) |
0 |
degrees C |
Temperature corresponding to Ik(1s) |
TR
Specification of the temperature, for which the specified conductor resistance applies. It enables the calculation of the resistance at another temperature (Tact), using the correction factor:
(1+0.004(Tact-20)) / (1+0.004(TR-20)).
Calculation of the maximum short-circuit current according to IEC 60909 is performed using a conductor temperature of 20 degrees C.
X
The line operational reactance must be larger than zero. A small impedance sometimes is required for a short coupling connection, but a value smaller than 1 mOhm is usually not realistic.
R0 and X0
For the calculation of short circuits with earth, the following two tests are conducted: R0> R1 and X0> 0. If either of these tests fail, a warning will be generated.
Inom
The nominal current must be specified and must be larger than zero.
TIk(1s)
The conductor temperature at Ik(1s) is used for calculating the minimum short-circuit current according to IEC 60909.
Reliability
The reliability parameters apply for the whole line. It is not possible to specify these parameters for each line part.
Parameter |
Default |
Unit |
Description |
Failure frequency |
0 |
per year |
Mean number of occurrences that the line fails (short circuit) |
Repair duration |
0 |
minutes |
Mean duration of repair or replacement |
Maintenance frequency |
0 |
per year |
Mean number of occurrences that the line 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 |
MODELLING
Pi-model
F the description of the pi-model see: Cable.
The tangent of delta is not applied for lines.
Inom'
For branches the terms Inom' and Snom' have been introduced for signalling an overload in the loadflow. These values have been introduced to obtain clarity about the maximum load capacity of a branch. For a connection, the value of Inom' is chosen from the input data according to the connection ampacity settings in the Options, at Calculation | Limits.
IEC 60909
For symmetrical short-circuit calculations, only the normal "longitudinal impedance" (R+jX) is used. The "transverse impedance" Xc is not taken into account.
In asymmetrical short-circuit calculations, the inverse impedance is equal to the normal impedance (Z1 = Z2). The pi-model with the zero sequence "transverse impedance" X0c applies to the zero sequence impedance (Z0).
The zero sequence data are not relevant to the calculation of a symmetrical fault (PPP) or a two-phase fault without earth contact (PP).
For the calculation of short circuits with earth, the following two tests are conducted: R0> R1 and X0> 0. If either of these tests fail, a warning will be generated.
The maximum admissible short-circuit time tmax is calculated using Ik,1s.
Calculation of the maximum short-circuit current according to IEC 60909 assumes a conductor temperature of 20 degrees C. The conductor temperature at Ik,1s is used for calculating the minimum short-circuit current according to IEC 60909.
The conductor resistance is specified for a reference temperature TR. The resistance for the actual temperature Tact will be calculated using the correction factor:
(1+0.004(Tact-20)) / (1+0.004(TR-20)).
Parallel lines
The electromagnetic influence in case of parallel lines can be modelled using the mutual coupling.
Harmonics
For the calculation of harmonics the distributed parameter model is used. See: Harmonics: Model