3-Phase Power: What is it?

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Three-phase power uses three wires to supply three independent alternating electric currents, providing a more stable flow of electricity than single-phase systems. It is commonly used in industrial settings for heavy machinery and electric motors, and is more efficient than single-phase power. The wires are color-coded differently in different countries, and irregularities can occur, so it is important to consult the schematic of the individual installation or system.

Three-phase power is a method of transmitting electricity that uses three wires to supply three independent alternating electric currents. The current in each wire is drawn away from the others by a third of a full cycle, with each current representing a phase. This means that a device operating on this type of power source receives a more stable flow of electricity than on a single-phase distribution system. Some three-phase power systems actually have four wires; the fourth is a neutral wire which allows the system to use a higher voltage.

The three currents together provide a balanced load, which is not possible with single-phase alternating current. In alternating current (AC), the current alternates direction, flowing back and forth in the circuit; this means that the voltage also alternates, continuously changing from maximum to minimum. Three-phase power combines the three wires to compensate for high and low swings, so a device receiving this type of power will not experience as large a voltage variation. This makes three-phase power a very efficient form of electrical power distribution. As a result, a three-phase electric motor consumes less electricity and typically lasts longer than a single-phase motor of the same voltage and power rating.

The flow of three-phase energy begins in a power plant, where an electrical energy generator converts mechanical energy into alternating electrical currents. After numerous conversions in the distribution and transmission grid, the energy is transformed into the standard voltage supplied to homes and businesses, 230 Volts in Europe or 120 Volts in North America. The transformer output usually connects to the power system using three live wires connected to a single grounded return. This is called a star connection.

This type of system doesn’t usually supply domestic homes with power, but when it does, a main distribution panel divides the load. Most household loads use single-phase power due to the lower cost of distribution. Three-phase power is more common in industrial settings or where more power is needed to operate heavy machinery, although there are exceptions.

Running electric motors are the most frequent use for three-phase power. A three-phase induction motor combines high efficiency, simple design and high starting torque. Industrial fans, blowers, pumps, compressors, and many other types of equipment commonly use this type of electric motor. Other systems that can use three-phase power include air conditioning equipment, electric boilers, and large rectifier systems used to convert alternating current to direct current.

While most motors that run on three-phase power are quite large, there are examples of very small motors, such as those that power computer fans, that run on this type of power. An inverter circuit inside the fan converts direct current (DC) into three-phase AC current. This is to reduce noise, as the torque of a three-phase motor is very smooth.
The wires, called conductors, used in a three-phase power system are normally color-coded, although colors vary greatly by location, and most countries have their own codes. North America traditionally uses black, red, and blue to represent the three phases, for example, while white represents the neutral wire. In Europe, by contrast, brown, black and gray represent phases and the neutral wire is blue. Even with these national standards, there tends to be a lot of irregularities in day-to-day applications. It is not a good idea for anyone working with three-phase power to make assumptions without consulting the schematic of the individual installation or system in question.

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