Three-phase electric power is a common type of alternating current (AC) used in electricity generation, transmission, and distribution. It is a type of polyphase system employing three wires and is the most common method used by electrical grids worldwide to transfer power.
A polyphase system is a means of distributing alternating-current (AC) electrical power that utilize more than one AC phase, which refers to the phase offset value between AC in multiple conducting wires; phases may also refer to the corresponding terminals and conductors, as in color codes. Polyphase systems have two or more energized electrical conductors carrying alternating currents with a defined phase between the voltage waves in each conductor; early systems used 4 wire two-phase) with a 90° phase angle but for three-phase voltage, the phase angle is 120° or 2π/3 radians as Dolivo-Dolobrovolsky mathematically had shown this reduce the magnetic field fluxuation from 40% to a mere 15%. Polyphase systems are particularly useful for transmitting power to electric motors which rely on alternating current to rotate. The most common example is the three-phase power system used for industrial applications and for power transmission. Compared to a single-phase, two-wire system, a three-phase three-wire system transmits three times as much power for the same conductor size and voltage.
IEC 60309 is a series of international standards from the International Electrotechnical Commission (IEC) for "plugs, socket-outlets and couplers for industrial purposes". They are also referred to as "pin & sleeve" connectors in North America or as "CeeForm" connectors in the entertainment industry. The maximum voltage allowed by the standard is 1000 V DC or AC; the maximum current, 800 A; and the maximum frequency, 500 Hz. The ambient temperature range is −25 °C to 40 °C.
In electrical engineering, ground and neutral are circuit conductors used in alternating current (AC) electrical systems. The ground circuit is connected to earth, and neutral circuit is usually connected to ground. As the neutral point of an electrical supply system is often connected to earth ground, ground and neutral are closely related. Under certain conditions, a conductor used to connect to a system neutral is also used for grounding (earthing) of equipment and structures. Current carried on a grounding conductor can result in objectionable or dangerous voltages appearing on equipment enclosures, so the installation of grounding conductors and neutral conductors is carefully defined in electrical regulations. Where a neutral conductor is used also to connect equipment enclosures to earth, care must be taken that the neutral conductor never rises to a high voltage with respect to local ground.
An autotransformer is an electrical transformer with only one winding. The "auto" prefix refers to the single coil acting alone. In an autotransformer, portions of the same winding act as both the primary winding and secondary winding sides of the transformer. In contrast, an ordinary transformer has separate primary and secondary windings that are not connected by an electrically conductive path. between them.
A zigzag transformer winding is a special-purpose transformer winding with a zigzag or "interconnected star" connection, such that each output is the vector sum of two (2) phases offset by 120°. It is used as a grounding transformer, creating a missing neutral connection from an ungrounded 3-phase system to permit the grounding of that neutral to an earth reference point; to perform harmonic mitigation, as they can suppress triplet harmonic currents; to supply 3-phase power as an autotransformer ; and to supply non-standard, phase-shifted, 3-phase power.
A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary.
A distribution transformer or service transformer is a transformer that provides the final voltage transformation in the electric power distribution system, stepping down the voltage used in the distribution lines to the level used by the customer. The invention of a practical efficient transformer made AC power distribution feasible; a system using distribution transformers was demonstrated as early as 1882.
An earthing system or grounding system (US) connects specific parts of an electric power system with the ground, typically the Earth's conductive surface, for safety and functional purposes. The choice of earthing system can affect the safety and electromagnetic compatibility of the installation. Regulations for earthing systems vary among countries, though most follow the recommendations of the International Electrotechnical Commission (IEC). Regulations may identify special cases for earthing in mines, in patient care areas, or in hazardous areas of industrial plants.
Extra-low voltage (ELV) is an electricity supply voltage and is a part of the Low voltage band in a range which carries a low risk of dangerous electrical shock. There are various standards that define extra-low voltage. The International Electrotechnical Commission (IEC) and the UK IET define an ELV device or circuit as one in which the electrical potential between two conductors or between an electrical conductor and earth (ground) does not exceed 50 V AC or 120 V DC.
In AC electrical power systems, a synchroscope is a device that indicates the degree to which two systems are synchronized with each other.
In electrical engineering, dot marking convention, or alphanumeric marking convention, or both, can be used to denote the same relative instantaneous polarity of two mutually inductive components such as between transformer windings. These markings may be found on transformer cases beside terminals, winding leads, nameplates, schematic and wiring diagrams.
A delta-wye transformer is a type of three-phase electric power transformer design that employs delta-connected windings on its primary and wye/star connected windings on its secondary. A neutral wire can be provided on wye output side. It can be a single three-phase transformer, or built from three independent single-phase units. An equivalent term is delta-star transformer.
A Scott-T transformer or Scott connection is a type of circuit used to produce two-phase electric power from a three-phase source, or vice versa. The Scott connection evenly distributes a balanced load between the phases of the source. The Scott three-phase transformer was invented by Westinghouse engineer Charles F. Scott in the late 1890s to bypass Thomas Edison's more expensive rotary converter and thereby permit two-phase generator plants to drive three-phase motors.
An AC motor is an electric motor driven by an alternating current (AC). The AC motor commonly consists of two basic parts, an outside stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft producing a second rotating magnetic field. The rotor magnetic field may be produced by permanent magnets, reluctance saliency, or DC or AC electrical windings.
High-leg delta is a type of electrical service connection for three-phase electric power installations. It is used when both single and three-phase power is desired to be supplied from a three phase transformer. The three-phase power is connected in the delta configuration, and the center point of one phase is grounded. This creates both a split-phase single phase supply and three-phase. It is called "orange leg" because the L3 wire is often required to be color-coded orange. By convention, the high leg is usually set in the center lug in the involved panel, regardless of the L1-L2-L3 designation at the transformer.
A variety of types of electrical transformer are made for different purposes. Despite their design differences, the various types employ the same basic principle as discovered in 1831 by Michael Faraday, and share several key functional parts.
A padmount or pad-mounted transformer is a ground-mounted electric power distribution transformer in a locked steel cabinet mounted on a concrete pad. Since all energized connection points are securely enclosed in a grounded metal housing, a padmount transformer can be installed in places that do not have room for a fenced enclosure. Padmount transformers are used with underground electric power distribution lines at service drops to step down the primary voltage on the line to the lower secondary voltage supplied to utility customers. A single transformer may serve one large building or many homes.
Voltage transformers (VT), also called potential transformers (PT), are a parallel-connected type of instrument transformer. They are designed to present a negligible load to the supply being measured and have an accurate voltage ratio and phase relationship to enable accurate secondary connected metering.
A grounding transformer or earthing transformer is a type of auxiliary transformer used in three-phase electric power systems to provide a ground path to either an ungrounded wye or a delta-connected system. Grounding transformers are part of an earthing system of the network. They let three-phase systems accommodate phase-to-neutral loads by providing a return path for current to a neutral.
