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In electrical engineering, three-phase electric power systems have at least three conductors carrying alternating current voltages that are offset in time by one-third of the period. A three-phase system may be arranged in delta (∆) or star (Y) (also denoted as wye in some areas). A wye system allows the use of two different voltages from all three phases, such as a 230/400 V system which provides 230 V between the neutral (centre hub) and any one of the phases, and 400 V across any two phases. A delta system arrangement only provides one voltage magnitude, however it has a greater redundancy as it may continue to operate normally with one of the three supply windings offline, albeit at 57.7% of total capacity.〔http://www.ibiblio.org/kuphaldt/socratic/output/deltawye_instructor.pdf public domain〕 Harmonic currents in the neutral may become very large if non-linear loads are connected. ==Definitions== In a star (wye) connected topology, with rotation sequence L1 - L2 - L3, the time-varying instantaneous voltages can be calculated for each phase A,C,B respectively by: : : : where: : is the peak voltage, : is the phase angle in radians :: is the time in seconds :: is the frequency in cycles per second and :voltages L1-N, L2-N and L3-N are referenced to the star connection point. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Three-phase」の詳細全文を読む スポンサード リンク
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