3. Simulation results, discussions

In order to estimate the changes regarding the harmonic conditions in a bus of a network, due to the installation of transversal impedance, it means to determinate the new harmonic voltages and harmonic currents, using the initial state of the network.

The validation of the mathematical model was done on a distribution electrical network comprising three voltage levels: 20, 6, and 0.4 kV, respectively. The configuration of the network and the main characteristics of its elements are presented in Figure 2.

To simulate the permanent normal operating conditions, the MatLab Simulink soft is used.

The harmonic regimen was obtained using harmonic current sources for the harmonics 5, 7, and 13, in three of the busses of the network (noted 1, 2, 3)—the load busses. These harmonic sources model the nonlinear components of the loads.

### 12 MATLAB - Professional Applications in Power System

Figure 2. The electrical distribution network used to validate the mathematical model.

For the validation of the mathematical model, bus no. 3 was selected.

The transversal impedance that will be installed has a capacitive character, and it corresponds to 0.3 MVAr capacitive reactive power on the fundamental frequency. The installation of a CB for power factor correction or the voltage control is an operation with a high impact for both the network and the capacitors. If the network contains harmonics, the effect of connecting a capacitor bank will be harmonic conditions amplification and capacitors thermal overstressing risk.

The ampleness of both effects can be anticipated using the state values of the network before the installation like it was proved earlier.

The amounts obtained by MatLab simulation before the installation of the CB are presented in Table 1. The notation represents the equivalent impedance of the linear component of the load.

By the successively installation of a CB having 0.3 MVAr capacitive reactive power, the values obtained using the method presented in this chapter, respectively, by MatLab simulation, are written in Tables 2 and 3.

The simulation was deliberately done for a case with high harmonic conditions—see the values in Table 1. It results in THDU ¼ 20% for the bus 3, before the reactive power compensation. For the bus 3, where is connected also a load, for the current absorbed by this, we have THDI ¼ 19%. We only concentrate on the linear component of the load connected in bus 3. From Table 3, we observe that after the reactive power compensation, the voltage THD in the


Table 1. The values from steady-state operation before the capacitor bank switching.

MatLab Simulink Modeling for Network-Harmonic Impedance Assessment: Useful Tool to Estimate Harmonics… 13 http://dx.doi.org/10.5772/intechopen.76461


Table 2. The values calculated after the capacitor bank switching.


Table 3. The values obtained by MatLab simulation after the capacitor bankswitching.

bus 3 will increase to 24.11%. This is due to the high distortion of the current that will flow through the capacitive impedance after its installation.

Comparing now the values obtained by calculus (Table 2) with the values measured in MatLab (Table 3), we observe a good proximity.
