Three-phase current, also known as three-phase alternating current, is a system used worldwide for the transmission of electrical energy. It involves three alternating voltages, each of which is generated with a 120° time offset. This phase shift results in a continuous, rotating magnetic field, which is ideal for operating machines. This staggered arrangement allows the current to be distributed more efficiently and evenly than with a simple alternating current.
In contrast to direct current, where the direction of current remains constant, or single-phase alternating current, three-phase alternating current is more powerful and is therefore used in industry, trade and increasingly also in the private sector.
In the European electricity grid, voltages of 230 volts between one phase conductor and the neutral conductor and 400 volts between two phase conductors are typically used. The three phases (i.e. the three outer conductors) each carry their own alternating voltage, which is offset in time. The interaction of these three phases results in a constant total power.
The rule is: If all three phases are equally loaded, no current flows through the neutral conductor. This results in a lower electrical load on the conductors, which saves material and minimizes losses. Although this technology requires more conductors, it offers better utilization and lower losses. The same energy can be transmitted with less heat generation.
A three-phase system consists of three outer conductors, often supplemented by a neutral conductor and a protective conductor. In power stations and generators, three coils are arranged at an angle of 120° to each other. When the rotor turns, a sinusoidal alternating voltage is generated in each coil – albeit with a time delay. This principle is used to ensure a constant power output.
This technology is used particularly for electric motors. An electric three-phase motor uses the resulting rotating magnetic field directly to generate mechanical energy. No additional starting mechanism is required. This saves on components, reduces maintenance costs and increases efficiency. This is precisely why three-phase current is used in almost every industrial motor.
Two typical circuits are used in the three-phase current range: the star connection and the delta connection.
In the star connection, the ends of the three coils are connected to each other – the so-called star point. There is a voltage of 230 V between one phase conductor and the neutral conductor and 400 V between two phase conductors. This circuit is often used in the home or for appliances that require less power.
The delta connection connects the coils together in a ring. No neutral conductor is used here and the voltage between the conductors is always 400 V. It is often used for motors and powerful machines where the full mains voltage is to be used.
Three-phase current offers many advantages over other types of current such as direct current or single-phase alternating current:
These advantages mean that three-phase current is now the standard in the public power supply.
Three-phase alternating current is used wherever high power is required with a simultaneous efficient supply of electrical loads – especially for appliances with high electrical loads. These include
Even renewable energies such as wind and hydropower usually generate three-phase current directly, which is then fed into the public grid.
Three-phase current, also known as three-phase alternating current, has become an integral part of the modern world. Thanks to its time-shifted alternating voltages, the even distribution of the current and the high voltage of up to 400 volts, it is ideal for a wide range of applications. Whether for operating a motor, supplying large consumers or efficient energy transmission – three-phase current works, reliably and powerfully.
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