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Three-phase transformer with four-wire output for 208Y/120 volt service: one wire for neutral, others for A, B and C phases. Three-phase electric power (abbreviated 3ϕ [1]) is a common type of alternating current (AC) used in electricity generation, transmission, and distribution. [2]
A typical one-line diagram with annotated power flows. Red boxes represent circuit breakers, grey lines represent three-phase bus and interconnecting conductors, the orange circle represents an electric generator, the green spiral is an inductor, and the three overlapping blue circles represent a double-wound transformer with a tertiary winding.
For example, balanced two-phase power can be obtained from a three-phase network by using two specially constructed transformers, with taps at 50% and 86.6% of the primary voltage. This Scott T connection produces a true two-phase system with 90° time difference between the phases.
Lighting and general purpose receptacles are at 120 volts AC, with larger devices fed by three wire single-phase circuits at 240 volts. In commercial construction, three-phase circuits are often used. Common 3 phase configurations within a building are 208v/120 wye, 120/240 center tapped delta and 480v/277v wye. Lighting is usually fed by 277 V ...
Wire crossover symbols for circuit diagrams. The CAD symbol for insulated crossing wires is the same as the older, non-CAD symbol for non-insulated crossing wires. To avoid confusion, the wire "jump" (semi-circle) symbol for insulated wires in non-CAD schematics is recommended (as opposed to using the CAD-style symbol for no connection), so as to avoid confusion with the original, older style ...
Y14.3–2003: Multiview and sectional view drawings Y14.31–2008: Undimensioned drawings Y14.36M–1996: Surface texture symbols Y14.38–2007: Abbreviations and acronyms for use on drawings and related documents Y14.4M–1989: Pictorial drawing Y14.41–2003: Digital product definition data practices Y14.42–2002: Digital approval systems ...
In addition, applying a trigger at a controlled phase angle of the AC in the main circuit allows control of the average current flowing into a load (phase control). This is commonly used for controlling the speed of a universal motor , dimming lamps, and controlling electric heaters.
Phase rotation is always counterclockwise (internationally adopted convention) and indicates multiples of 30 degree lag for low voltage winding using of the high voltage winding as the reference. Thus 1 = 30°, 2 = 60°, 3 = 90°, 6 = 180° and 12 = 0° or 360°. According to the IEC60076-1 standard, the notation is HV-LV in sequence.