Influence of the Phase Angle Variation of Harmonic Sources on the Voltage THD Level of Power Grids

This paper investigates the influence of the phase angle variation of Harmonic Sources (HSs) on the voltage Total Harmonic Distortion (THD) of power grids. Most standards allocate some limits only for the magnitude of harmonic sources to restrict the voltage THD level of power grids, whereas the phase angle of harmonic sources can play a significant role in this regard. Harmonic sources can cancel or reinforce each other depending on their phase angle difference. This paper aims to answer what types of harmonic sources cancel each other, and what types of them reinforce each other. For this purpose, this paper investigates the effect of the so-called prevailing ratio of harmonic sources, describing the stochastic and time-varying behavior of harmonic source phase angle, on the voltage THD. This paper applies a probabilistic harmonic power flow method based on Monte-Carlo-Simulations to a distribution grid to consider the stochastic behavior of harmonic phase angles. The results show that the prevailing ratio of harmonic sources has a considerable impact on the grids voltage THD level, especially in the case that the number of harmonic sources from a specific type is relatively high (e.g., a specific type of converter in a particular power grid). Therefore, the prevailing ratio of harmonic sources can be employed in standard guidelines as an indicator that affects the voltage THD and, consequently, the power quality.