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Polyphase electrical systems supply alternating current electrical power in overlapping phases. The most common, and almost universal, examples are three-phase power systems. Three phase power is commonly found in industrial applications and LCR circuits.1 Phases
These systems exhibit three-phase induction or more. Three phase power is commonly found in industrial applications. Normal household supply consists of a sine wave of alternating polarity, with the voltage rising and falling over time. This is called single phase electric power.
A few older installations in the U.S. used two phase four-wire systems for motors. The chief advantage of these was that the winding configuration was the same as for a single-phase capacitor-start motor. Most of these have been upgraded to three-phase systems. A two-phase supply with 90 degrees between phases can be derived from a three-phase system using transformers in a Scott connection . In North America most households are equipped with single-phase circuits supplied from a transformer in which the secondary winding is 120/240 volts (nominal) three-wire with neutral. The phase alignment is 180°. These are used in high-energy appliances such as electric Ovens/ranges and clothes dryers. Such systems are sometimes refered to as split phase and are often incorrectly refered to as two phase.
2 Motors
Polyphase power is particularly useful in AC motors, where it can be used to generate a rotating magnetic field. Alternate current sine wave voltage points, when the field is graphed and analyzed, show a result of a magnetic field that is rotating (thus producing the alternating polarity). When a three-phase voltage completes one full cycle, the magnetic field has rotated through 360°. In a polyphase system several such supplies are overlapped out of phase to smooth out the total voltage.
3 Invention
Nikola Tesla invented this type of system. Polyphase electrical systems operate on the principle of the lead-lag effectA lead-lag effect especially in economics, describes the situation where one (leading) variable is correlated with the values of another (lagging) variable at later times. For example, economists have found that in some circumstances there is a lead-lag e in the rotating magnetic field produced by an alternating-current circuit. He found these systems during his research into harmonic oscillatorA harmonic oscillator is a mechanical system in which there exists a returning force F directly proportionate to the displacement x i. where k is a constant. It can also refer to any physical system that is analogous to this mechanical system, in which sos.
4 See also
- Alternating current
- Polyphase coilPolyphase coils are electrical coils (phases) connected together in a polyphase system such as a generator or motor. In modern systems the number of phases is usually three, or a multiple of three. Each phase carries a sinusoidal alternating current whose
Electrical engineeringElectrical engineering is an engineering discipline that deals with the study and application of electricity and electromagnetism. Its practitioners are called electrical engineer s. Electrical engineering is a broad field that encompasses many subfields.
Nikola Tesla
