How do you model frequency dependent network equivalents (FDNE) for harmonic analysis?
The full network model might not be available for the harmonic analysis or the full model has to be reduced for performance reasons. Examples are:
- Harmonic Analysis for a power plant (e.g. wind farm / solar farm): The detailed model of the power plant, e.g. wind farm, will be available. However, the network model for the transmission system might be provided.
- Harmonic Analysis in a distribution network: The detailed distribution network model is available, however, the transmission system is not.
- Harmonic Analysis in a transmission system: The detailed transmission network is available, however, the boundary transmission systems of the neighboring TSO's is not.
- Reduction of a large network to a smaller network in order to gain performance improvements
In all the above cases, the source network / surrounding network has to be modeled with network equivalents. It is recommended to use frequency dependent network equivalents (FDNE) for harmonic studies to represent the external network accurately.
The attached project "Network Equivalent" shows such a FDNE. The FDNE was derived from the project "Detailed Network Model" using the Frequency Sweep Calculation.
The Frequency Sweep Calculation was carried out in the detailed network model for two option scenarios:
- Base Case (normal operating condition): Operation Scenario 1
- Contingency Case (abnormal operating condition): Operation Scenario 2
Using the Frequency Sweep Calculation in PowerFactory, you can derive the frequency dependent network resistance and reactance for the positive, negative and zero sequence. This information (stored in the attached Excelsheet) is then used to derive frequency characteristics that are assigned to the external grid in the project "Network Equivalent".
The frequency characteristics are assigned to the external grid on the PowerQuality/Harmonic page. The characteristic is created as follows:
- Create a Frequency Scale (TriFreq) e.g. from 1 Hz to 2.5 kHz
- Create a Parameter Characteristic - Vector (ChaVec)
- Select the TriFreq
- Assign the characteristic e.g. from the attached Excel sheet as absolute values
- Assign the ChaVec on the Harmonics page of ElmXnet