Phase converter
Encyclopedia
A phase converter is a device that converts electric power provided as single phase
to multiple phase
or vice-versa. 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 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 for transformers and metering and the extra transmission wire.
Each of the above methods has its own set of advantages and drawbacks.
, electricity is normally generated as three-phase AC at 50 hertz
. Five European countries, Germany
, Austria
, Switzerland
, Norway
and Sweden
have standardised on single-phase AC at 15 kV 16⅔ Hz for railway electrification
. Phase converters are, therefore, used to change both the phase and the frequency
.
Single-phase electric power
In electrical engineering, single-phase electric power refers to the distribution of alternating current electric power using a system in which all the voltages of the supply vary in unison. Single-phase distribution is used when loads are mostly lighting and heating, with few large electric motors...
to multiple phase
Polyphase system
A polyphase system is a means of distributing alternating current electrical power. Polyphase systems have three or more energized electrical conductors carrying alternating currents with a definite time offset between the voltage waves in each conductor. Polyphase systems are particularly useful...
or vice-versa. 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 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 for transformers and metering and the extra transmission wire.
Conversion systems
Three phase induction motors may operate adequately on an unbalanced supply if not heavily loaded. This allows various imperfect techniques to be used. A single-phase motor can drive a three-phase generator, which will produce a high-quality three-phase source but with high cost for apparatus. Several methods exist to run three-phase motors from a single-phase supply, these can in general be classified as:- Electronic means of creating three phase where the incoming power is rectified, and the three phase power is synthesized with electronics. Power electronic devices directly produce a three-phase waveform from single-phase power, using a rectifierRectifierA rectifier is an electrical device that converts alternating current , which periodically reverses direction, to direct current , which flows in only one direction. The process is known as rectification...
and inverterInverter (electrical)An inverter is an electrical device that converts direct current to alternating current ; the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits....
combination. This also offers the advantage of variable frequency.
- A digital phase converter uses a rectifier and inverter to create a single voltage with power electronics, which is added to the two legs of the single-phase source to create three-phase power. Unlike a phase converting VFD, it cannot vary the frequency and motor speed since it generates only one leg which must match the voltage and frequency of the single-phase supply. It does have the advantage of a sine-wave output voltage and excellent voltage balance between the phases.
- Rotary phase converterRotary phase converterA rotary phase converter, abbreviated RPC, is an electrical machine that produces three-phase electric power from single-phase electric power. This allows three phase loads to run using generator or utility-supplied single-phase electric power....
s constructed from a three-phase electric motor or generator "idler". These normally require some kind of starting aid and capacitors to improve phase balance and power factor. This is a two motor solution. One motor is not connected to a load and produces the three phase power, the second motor driving the load runs on the power produced.
- Static conversion techniques in which the motor is run at less than full efficiency mainly on two of the legs of the three phase motor. Current is sometimes injected into the third leg with a capacitor or transformer arrangements that provide imperfect phase shift. In these systems the motor must be derated.
- Methods in which the connection of the windings of the motor, normally a wye and or delta configurations, are replaced with novel connections. These techniques are covered in patents of Dr. Otto J. M. SmithOtto J. M. SmithOtto J. M. Smith was an educator, inventor and author in the fields of engineering and electronics. He spent most of his career as a professor at University of California Berkeley. Dr...
, such as US Patent 5,545,965.
Each of the above methods has its own set of advantages and drawbacks.
Electric railways
In EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
, electricity is normally generated as three-phase AC at 50 hertz
Hertz
The hertz is the SI unit of frequency defined as the number of cycles per second of a periodic phenomenon. One of its most common uses is the description of the sine wave, particularly those used in radio and audio applications....
. Five European countries, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, Austria
Austria
Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
, Norway
Norway
Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...
and Sweden
Sweden
Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....
have standardised on single-phase AC at 15 kV 16⅔ Hz for railway electrification
Railway electrification system
A railway electrification system supplies electrical energy to railway locomotives and multiple units as well as trams so that they can operate without having an on-board prime mover. There are several different electrification systems in use throughout the world...
. Phase converters are, therefore, used to change both the phase and the frequency
Frequency changer
A frequency changer or frequency converter is an electronic device that converts alternating current 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.Traditionally, these devices were...
.
See also
- Rotary phase converterRotary phase converterA rotary phase converter, abbreviated RPC, is an electrical machine that produces three-phase electric power from single-phase electric power. This allows three phase loads to run using generator or utility-supplied single-phase electric power....
- Variable frequency driveVariable frequency driveA variable-frequency drive is a system for controlling the rotational speed of an alternating current electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive...
- Digital phase converterDigital phase converterA digital phase converter creates a three phase power supply from a single phase supply. A digital signal processor is used to control power electronic devices to generate a third voltage, which along with the single-voltage from the supply creates a balanced three-phase power supply.AC power from...
- Scott-T transformerScott-T transformerA Scott-T transformer is a type of circuit used to derive two-phase current from a three-phase source or vice-versa. The Scott connection evenly distributes a balanced load between the phases of the source....