Hydro One Networks: Effects of harmonics on power distribution system

Project goal: Hydro One Networks asked CARI to research the impacts of harmonic loads on distribution transformers. The impact of Electric Vehicle chargers, which are seen as the largest addition to electrical loads in many years, have also been a focus of the research.

To measure the harmonic content, often described as the percent total harmonic distortion (%THD), of the current that electrical devices draw while energized. Harmonics currents are a natural part of the energy drawn by electrical equipment, in particular, those appliances and devices that use a pulsing wave often observed when AC is covered to DC. Common examples include compact florescent bulbs and the majority of energy saving appliances including washing machines, microwave ovens, and entertainment devices (TV’s, DVD players, and computers).

What was done: In order to measure harmonic content, it was first necessary to create a way to measure harmonic currents drawn through standard household 120 V line conductors. Our research developed a standard household panel setup, which included loads that would be typically found in a household environment such as: kitchen appliances, computers, televisions, and alarm clocks. This panel allowed the researcher to attach loads in varying combinations and measure the amount of current drawn by the load(s), the harmonic content that the load(s) created, the amount of power consumed, and other relevant data. PVC plastic conduit was used to protect student researchers, as the material is transparent to the magnetic field around the conductors.

What was achieved: We observed that each static load/device and configuration has a unique harmonic spectrum and energy draw associated with it. The data of each configuration was used to create a model in ETAP (an electrical power systems design and analysis software) that represents loads on a representative distribution station. Through ETAP, we could then simulate and compare the impact of the different loads during peak hours to the off peak hours and determine if overloading occurred or if the harmonic distortion limits established by IEEE were exceeded.