# Evaluating Effects of Electric Vehicle Chargers on Residential Power Infrastructure
## 4 Impact on the Electrical System
### Harmonic Distortion Impact  
Harmonic effects in the system constitute another factor significantly impacting the electrical infrastructure where residents live. Distortions in current and voltage can reduce power quality, and the resulting harmonics can create distortions in the electrical waveform. This deviation from a pure sine wave can affect the quality of electricity and the operation of electrical equipment connected to the system. Sensitive devices, such as computers and appliances requiring high-quality electricity, may be damaged or malfunction due to current distortion. Traditional harmonic analysis focuses solely on the amplitude of individual harmonic orders; thus, this study adopts a time-domain perspective by examining real-time variations in the total harmonic distortion (THD) for both voltage and current throughout the EV charging periods. This approach provides greater insights into the operational impact of EV chargers under real-world conditions. Figure 10 presents the voltage THD across three phases (V\({}_{1}\), V\({}_{2}\), and V\({}_{3}\)). The plotted data show that voltage distortion generally remains below 2.5%, with observable cyclical patterns likely corresponding to daily load variations. During charging intervals, indicated by the shaded bands, slight but consistent increases in voltage THD can be observed, particularly in phases V\({}_{1}\) and V\({}_{2}\). Although the magnitude of distortion remains within acceptable limits, the repetitive elevation during EV charging suggests that harmonic voltage contributions from the charger are measurable and could accumulate under high-penetration scenarios. Figure 11 shows the current THD in phases I\({}_{1}\), I\({}_{2}\), and I\({}_{3}\) during the same period. The analysis reveals more pronounced effects: THD values increase sharply during active charging sessions, in some cases exceeding 15-20%. The variation across phases reflects the  
charging configuration, with single-phase charging typically concentrating on one phase. Phase I2 exhibits the highest variability and peak THD, likely due to an unbalanced load distribution and nonlinear current draw. These findings confirm that EV charging contributes significantly to current harmonic distortion, while voltage distortion remains comparatively moderate. The imbalance between phases also amplifies the distortion in the neutral conductor, further compounding the issue. The presence of harmonic distortion in electrical systems, particularly under EV charging conditions, can result in multiple adverse effects that compromise both performance and reliability. One of the primary concerns is harmonic resonance, which can amplify certain frequency components in the system and lead to overvoltage conditions or damage to connected equipment. Additionally, increased harmonic currents contribute to thermal stress in electrical components such as transformers, conductors, and especially neutral lines, accelerating insulation aging and reducing the overall system lifespan. Measurement errors may also occur, particularly in metering and protection systems, as harmonics can interfere with the accuracy of instruments that assume sinusoidal wave  
Figure 10: Voltage harmonic distortion observed during EV charger operation: (**a**) time series of voltage THD and (**b**) distribution and cumulative frequency of voltage THD. forms. Furthermore, harmonics may cause electromagnetic interference (EMI) with nearby communication systems and sensitive electronic devices, leading to operational instability. These cumulative effects, if left unmanaged, can degrade the performance of residential power systems over time, even in environments without highly sensitive loads. Therefore, proactive measures should be considered to assess and mitigate harmonic distortion, particularly in buildings undergoing EV charger integration. To mitigate these effects, a range of strategies can be considered, such as active or passive harmonic filters, load balancing techniques, and the use of harmonic-tolerant devices.