# Effect of Harmonics on Ferroresonance in Low Voltage Power Factor Correction System--A Case Study
## 4 Experimental Results and Discussion
### Experimental Results for C2
The waveforms of the reactor voltage, the capacitor voltage, and the capacitor stage current in the steady state of the ferroresonance are shown in Figure 17. The stage current is highly distorted, which is a consequence of the deep saturation of the reactor. The maximum stage current reaches 1000 A, and the maximum reactor voltage reaches 344.0 V. According to [12], the current waveform exhibits quasi-periodic oscillations. The harmonic spectrum of reactor voltage, capacitor voltage and stage current is shown in Figure 18. Compared with the spectrum in Figure 11, which is given for the normal steady state, the harmonic content of the voltages and currents is much higher. It can be seen that the current harmonics of the stage current have enormous values. The 5 th harmonic of the stage current is 189.0 A, while the 7 th harmonic is 62.1 A. Since the ferroresonance can occur at different frequencies, the spectrum should be further analyzed in the continuous domain. Figure 19 shows how the reactor magnetic flux depends on the reactor current at steady state in C2. The hysteresis shows that during the ferroresonance all three phases of the detuned reactor go into saturation. Figure 11:0 C2—Capacitor voltage, reactor voltage and stage current after the stage is switched on. Figure 11:1 C2—Harmonic spectrum of reactor voltage, capacitor voltage and stage current in ferroresonance steady state. The voltage and current waveforms of the medium voltage feeder are shown in Figure 11:2 The voltage and current waveforms are more distorted than those shown for C1. The distortion of the current is \(THD_{l,T1}=7.8\%\) and the distortion of the voltage is \(THD_{U,T1}=2.0\%\). Figure 21 shows the vector diagram of the 5 th harmonic voltage and current of the medium voltage feeder before and after the capacitor stage was switched on. Before the stage was switched on, the 5 th harmonic current was 10.8 A and flowed into the medium voltage grid, and after the stage was switched on, the 5 th harmonic current was 12.6 A and flowed from the medium voltage grid to the transformer station. The ferroresonance distorted the currents and voltages on the medium voltage side, which confirms that the power system supports the ferroresonance. The ferroresonance in C2 was triggered by switching on the capacitor stage. The capacitor stages switched on before reaching C2 operate under normal conditions. Figure 22 shows the voltage and current of transformer T1 and the stage current in C2 when the ferroresonance is not triggered. The stage current waveform is typical, but the harmonic spectrum shows the high value of the 5 th harmonic. The RMS value of the stage current is \(I_{S}=84.8\) A, and the 5 th harmonic current is \(I_{S,5}=48.6\) A, which is higher than the allowable value given in Figure 11:3 Therefore, the reactor may be overloaded with harmonic currents if the harmonic distortion is high. Figure 11:4 C2—Hysteresis loop of reactor. Figure 11:5 C2—Medium voltage feeder voltage and current in ferroresonance steady state.