Understanding Phase Power: Single Phase Frequency Changer
In AC electrical power systems, phase is a definition of the position of a point in time (instant) on a waveform cycle. A complete cycle is defined as 360 degrees of phase as shown below.
The simplest form of electrical power is a single-phase power converter. This is represented by a single sine wave.
Single-phase line conditioners are used when loads are mostly lighting and heating, with few large electric motors. In North America, individual residences and small commercial buildings with services up to about 100 KVA (417 amperes at 240 volts) will usually have three-wire single-phase distribution, often with only one customer per distribution transformer.
Typically a third conductor, called ground or protective earth ground, is used as a protection against electric shock, and ordinarily only carries significant current when there is a circuit fault. Phase can also be an expression of relative displacement between or among waves having the same frequency.
What is a Phase Converter?
A phase converter is a device that converts electric power provided as a single-phase to simulated three phases. The majority of phase converters are used to produce three-phase electric power from a single-phase source, thus allowing the operation of three-phase equipment at a site that only has single-phase electrical service. Phase converters are used where a three-phase service is not available from the utility or is too costly to install due to a remote location. A utility will generally charge a higher fee for a three-phase service because of the extra equipment, including transformers, metering, and distribution wire.
The quality of the three-phase output is poor but good enough to run a motor load. Since motors above 10 HP tend it be 3 phase only, phase converters are often used to drive larger motor loads.
What is a Frequency Converter?
A frequency changer or frequency converter is an electronic (solid-state) or electromechanical (motor-generator set) device that converts alternating current (AC) of one frequency to alternating current of another frequency. The device may also change the voltage, but if it does, that is incidental to its principal purpose, since voltage conversion of alternating current is much easier to achieve than frequency conversion.
Traditionally, these devices were electromechanical machines (motor-generator sets). With the advent of solid-state electronics, it has become possible to build completely electronic frequency changers. These devices usually consist of a rectifier stage (producing direct current) which is then inverted to produce AC of the desired frequency. The inverter may use thyristors or IGBTs. If voltage conversion is desired, a transformer will usually be included in either the AC input or output circuitry and this transformer may also provide galvanic isolation between the input and output AC circuits.