# Multi-Point Time-Synchronized Waveform Recording for the Analysis of Wide-Area Harmonic Propagation
## 4 Results
### Multiple Harmonic Sources under Sinusoidal Power Supply  
The simultaneous operation of devices injecting harmonics into grid is analyzed in this section. The loads studied in this test case are PV inverter, EV charger, and synthetic harmonic load emulated by Triphase. The system is energized by MG power supply set (sequence A.4). In Figure 7, synchronized voltage spectral components extracted from all points available for voltage measurements are shown. This plot contains components which were otherwise not present in previous cases. The drastic increase of voltages up to 30 V at 850 Hz and up to 22 V 950 Hz at MV side is clearly visible. Additionally, at 550 Hz, the recorded harmonic voltage value was approximately 11 V. It is obvious to note that no substantial difference was observed between voltages at Primary Switchboard (Isolation Transformer) and MV side of Substation G. The reason for this is relatively small electrical distance between these two points. In order to gain insight into the reasons behind such harmonic response of the studied network, the synchronized substation currents were processed and results are demonstrated in Figure 8. The currents through Substation A are significantly higher than through Substation G for every frequency except 1150 Hz and 1250 Hz harmonic components. By looking at individual currents of every connected harmonics source, more details can be revealed. In Figure 9, the synchronized current spectra of PV inverter and EV charger are presented. Whilst the emissions of PV are blurred with significant amount of subharmonics, the harmonic currents of EV charger coincide with measured voltages. Figure 7: Harmonic voltages at multiple points. Test sequence A.4—MG set supply. Furthermore, the Triphase connected to substation A was programmed as a substantially large source of harmonic current injections with a purpose of acting as reference device with fixed harmonic emissions. The values of harmonic currents for this load are presented in Table 2 for frequences 150 Hz to 1050 Hz. It is worth noting that harmonic phase angles for every order were set to 0. \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline
**3 rd** & **5 th** & **7 th** & **9 th** & **11 th** & **13 th** & **15 th** & **17 th** & **19 th** & **21 st** \\ \hline
1.055 & 6.07 & 2.312 & 0.225 & 2.167 & 2.805 & 0.588 & 3.324 & 1.644 & 0.091 \\ \hline \end{tabular}
\end{table} 
Table 2: Currents of emulated harmonic source (in A). Figure 8: MV harmonic currents through transformers. Test sequence A.4—MG set supply. Figure 9: Individual harmonic currents of PV and EV chargers. Test sequence A.4—MG set supply. Next, the measured harmonic currents of this device are shown in Figure 10. In comparison with Figure 7, the conclusions can be drawn that this emulated load acted as dominant source of harmonics provoking large harmonic voltage drops at 550 Hz, 850 Hz, and 950 Hz on the LV side of Substation A. This distortion in turn propagated towards the MV system and down to the LV side of Substation G. Moreover, while the 5 th harmonic current injected by Triphase is substantial (6.07 A), it did not cause a significant voltage drop at this frequency at a medium voltage level. The reason for this is relatively small low-voltage impedance at this frequency which resulted on average in some 0.5 V of harmonic voltage drop at an LV level. Propagating further upstream, the resulting harmonic current phasor interacting with impedance angle at this particular frequency produced additionally about 3 V.  
It is interesting to observe that this complex interaction between harmonic current phasors and system impedances provoked a significant decrease of voltage at 1250 Hz from 63 V (case A.2) to about 32 V. Since the emulated harmonic load was not programmed to inject current at this frequency, we shall look again at Figures 8 and 9 in order to evaluate harmonic current emissions of PV and EV chargers.