Circuit polyphase

Circuits that carry AC current employing two, three, or more sinusoidal potentials are C2 ed polyphase circuits. Polyphase circuits provide for more efficient generation and transmission of power than single-phase circuits. Power in a three- (or more) phase circuit is constant rather than pulsating like the single-phase circuit. As a result, three-phase motors operate more efficiently than single-phase motors. 

Electrical Units 278. Electrical Circuit Elements 281. Transient and AC Circuits 284. AC Power 285. Magnetism 286. Transformers 288. Rotating Machines 289. Polyphase Circuits 293. Power Transmission and Distribution Systems 294. 

Wound-Rotor Induction Motor. A wound-rotor induction motor is an induction motor in which the secondary circuit consists of a polyphase winding or coils whose terminals are either short circuited or closed through suitable circuits. 

Single-phase motors may be started (a) by incorporating a commutator, (6) by hand and (c) by operating them as polyphase motors, a phase splitter being used to throw two or more circuits out of phase with each other. ... 

Phase sequence is the order in which each phase of a three-phase supply reaches its maximum value. The normal phase sequence for a three-phase supply is brown-black-grey, which means that first brown, then black and finally the grey phase reaches its maximum value. lET Regulation 612.12 tells us that for polyphase circuits a test must be made to verify that the phase sequence is maintained. 

Phase The number of circuits over which electric power is supplied. In a single-phase motor, power is supplied in a single circuit or winding. In a three-phase system, power is provided over three circuits, each circuit reaching corresponding cyclic values at 120° intervals. AC motors are typically qualified as single-phase or polyphase. 

Phase-failure protection Protection provided when power fails in one wire of a polyphase circuit to cause and maintain the interruption of power in all wires of the circuit. 

Phase-reversal protection The prevention of motor energizing under conditions of phase sequence reversal in a polyphase circuit. 

Required the neutral, in single-phase circuits, to have a cross-sectional area of not less than the phase conductor and, in polyphase circuits, the neutral to be of adequate size for the anticipated current (section 524-02-01). 

In polyphase circuits. Regulations 524-02-01 and 02 warn against the use of reduced size neutrals where there are unbalanced loads and/or additive harmonic currents, and for this reason Regulation 524-02-03 forbids their use in discharge lighting circuits where the harmonic content of the phase currents is greater than 10% of the fundamental current. 

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