The source is a fictitious network element which is necessary to carry out load flow calculations. The source (swing bus) "supplies" the difference between generation and load, including the network losses, in load flow calculations. The source can thus also be considered for load flow calculations as a connection with an infinitely powerful network. For a calculation on a 10 kV network, for example, it is thus best to incorporate the 150 kV/10 kV supply transformer and place the source on the 150 kV side of the transformer.
In order to enable more realistic performance of short-circuit calculations on a network with a source, the short-circuit power must be given in kA, Ohm or MVA.
Use Appearance to switch between the possible short-circuit power indicators.
Only one source can be present at a node.
PARAMETERS
Source
Parameter |
Default |
Unit |
Description |
Name |
|
|
Name |
Uref |
1 |
pu |
Reference voltage as a factor of Unom |
Profile |
Default |
|
Name of the voltage profile |
Angle |
0 |
degrees |
Reference voltage phase angle |
Sk"nom |
100 * Unom |
MVA |
Sub-transient short-circuit power |
Sk"min |
90 * Unom |
MVA |
Minimum sub-transient short-circuit power |
Sk"max |
100 * Unom |
MVA |
Maximum sub-transient short-circuit power |
Ik"nom |
|
kA |
Sub-transient short-circuit current |
Ik"min |
|
kA |
Minimum sub-transient short-circuit current |
Ik"max |
|
kA |
Maximum sub-transient short-circuit current |
Znom |
|
Ohm |
Impedance |
Zmax |
|
Ohm |
Maximal impedance |
Zmin |
|
Ohm |
Minimal impedance |
R/X |
0 or 0,1 |
|
Ratio between source impedance R and X |
Z0/Z1 |
1 |
|
Ratio between source impedance zero and normal sequence |
Smin |
0 |
MVA |
Minimal to be tested power |
Smax |
0 |
MVA |
Maximal to be tested power |
Harmonics
Parameter |
Default |
Unit |
Description |
h |
3 t/m 99 |
|
Harmonic number |
Voltage |
0 |
% |
Harmonic voltage, relative to rated voltage |
Angle |
0 |
degrees |
Harmonic voltage angle, relative to load flow voltage |
Reliability
Parameter |
Default |
Unit |
Description |
Failure frequency |
0 |
per year |
Mean number of occurrences that the source fails (short circuit) |
Repair duration |
0 |
minutes |
Mean duration of repair or replacement |
Maintenance frequency |
0 |
per year |
Mean number of occurrences thet the source 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
A network usually has only one source. In Vision it is possible to have several sources, but caution is required. A source has a fixed voltage in size and angle. When multiple sources are connected, different angles might be calculated for the network with respect to practice. In a network consisting of multiple sources, it is best to use only one source. If the grid is powered by an "external grid" at various locations, it is best to work with an equivalent for the external grid, in which only one source is included.
Load flow
Uref can be used to give the voltage of the source in pu. This Uref is a factor of the Unom of the node concerned stated in the source form. The following applies for each node to which a source is added:
|U| = Uref * Unom node
angle = angle
so that the voltage at the node always remains constant, with the define angle.
During the motor start calculation the source is modelled as an equivalent voltage behind its sub-transient impedance:
Uequivalent = Uref + Iload flow,pre * Zsource
IEC 60909
In IEC 60909 calculations, a source is represented as a passive impedance to earth (IEC 60909, clause 3.2)
For the source, the short-circuit power is given in kA or MVA. The impedance of the source is determined in accordance with the formula below. The following applies for the impedance of the source:
Zsource = c * Unom / (√3 * Ik")
where:
|
the voltage factor cmax or cmin (depending on minimum or maximum short-circuit current calculation) associated with the Unom of the node of the source. |
||
Ik" |
the sub-transient short-circuit current of the source |
With asymmetrical short-circuits, the normal impedance is equal to the inverse impedance (Z1 = Z2). The zero sequence impedance Z0 is determined using the ratioIk"3/Ik"1:
This can be rewritten as:
Fault analysis
In the sequential fault analysis, the source is represented as a Norton equivalent. The R/X ratio of the source impedance is determined in the same way as in an IEC 60909 calculation.
Ik" is used to determine the short-circuit power of the source instead of Ik"max or Ik"min.