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Single-phase motors may have taps to allow their use on either 208-volt or 240-volt supply. A single-phase load may be powered directly from a three-phase distribution transformer in two ways: by connection between one phase and neutral or by connection between two phases. These two give different voltages from a given supply.
The center tap is grounded and one pole is fed to an overhead wire section, while the other wire is used for another section. Split-phase distribution is used on Amtrak's 60 Hz traction power system in the Northeast Corridor between New York and Boston. Two separate wires are run along the track, the contact wire for the locomotive and an ...
The equivalent power rating of the autotransformer is lower than the actual load power rating. It is calculated by: load VA × (|Vin – Vout|)/Vin. [2] For example, an auto transformer that adapts a 1000 VA load rated at 120 volts to a 240 volt supply has an equivalent rating of at least: 1,000 VA (240 V – 120 V) / 240 V = 500 VA.
This allows one to choose single-phase AC power at either 110–120 volts between phase and neutral or 220–240 volts between phase and phase. Since these two modes do not need three phases there is also a dark yellow-orange four-pin connector available designed for a single-phase 110–120 or 220–240 volt load.
Current practice is to give separate services for single-phase and three-phase loads, e.g., 120 V split-phase (lighting etc.) and 240 V to 600 V three-phase (for large motors). However, many jurisdictions forbid more than one class for a premises' service, and the choice may come down to 120/240 V split-phase, 208 V single-phase or three-phase ...
A three-phase motor is more compact and less costly than a single-phase motor of the same voltage class and rating, and single-phase AC motors above 10 hp (7.5 kW) are uncommon. Three-phase motors also vibrate less and hence last longer than single-phase motors of the same power used under the same conditions. [32]
Such arrays will evenly balance the polyphase load between the phases of the source system. 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.
A motor capacitor [1] [2] is an electrical capacitor that alters the current to one or more windings of a single-phase alternating-current induction motor to create a rotating magnetic field. [ citation needed ] There are two common types of motor capacitors, start capacitor and run capacitor (including a dual run capacitor ).