Three-phase current - basics, structure and significance for the power supply

Three-phase current, also known as three-phase alternating current, is a system for transmitting electrical energy that is used worldwide. It involves three alternating voltages, each of which is generated with a 120° time shift. This phase shift results in a continuous, rotating magnetic field, which is ideal for the operation of machines. This time-shifted 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 modern electricity grids, this system forms the basis for the reliable supply of energy to cities, businesses and households. Three-phase current demonstrates its advantages over other electrical systems, particularly when it comes to transmitting large amounts of power.

Voltage, current and phases in the system

In the European electricity grid, a voltage of 230 volts is typically used between one phase conductor and the neutral conductor, and 400 volts between two phase conductors. 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.

In practice, this means that the electrical power is distributed evenly across the respective phases. This means that devices and systems can be operated stably without individual conductors being overloaded. This even distribution ensures reliable operation, especially in industrial systems where high electrical power is required.

Structure of a three-phase system

A three-phase system consists of three phase conductors, often supplemented by a neutral conductor and a protective conductor. These conductors are connected to each other in the power grid and ensure that electrical energy reliably reaches the individual consumers.

In power plants 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 – but out of phase. This principle ensures that electrical energy can be generated continuously. The individual alternating voltages complement each other to form a stable system that is particularly suitable for power supply.

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.

Another advantage can be seen in the transmission of electricity over long distances. As the electrical power is distributed over several phases, cables can be used more efficiently. At the same time, different voltages can be provided within the system, such as 230V for smaller devices or 400V for more powerful machines.

Circuits: Star and triangle

Two typical circuits are used in the three-phase current range: the star connection and the delta connection. Both variants differ in the way the coils are connected to each other and the voltages applied to the individual lines.

Star 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.

One advantage of the star connection is that both smaller electrical loads and more powerful appliances can be operated in the same system. The existing neutral conductor means that individual appliances can be supplied directly with 230 volts.

Delta connection

The delta connection connects the coils together in a ring. No neutral conductor is used here and the voltage between the conductors is always 400V. It is often used for motors and powerful appliances where the full mains voltage is to be used.

This connection creates a particularly powerful system that is primarily used in industrial applications. Many machines use the delta connection when high performance and stable operation are required.

Advantages of three-phase alternating current

Three-phase current offers many advantages over other types of current such as direct current or single-phase alternating current:

• Efficient transportation of large amounts of energy
• Equal distribution of the current to all three phases
• Reduced heat loss in the pipes
• Reduced material requirements with the same performance
• Directly usable rotating field for motors
• Choice between 230 V and 400 V for different loads

These advantages mean that three-phase current is now the standard in the public power supply. This system ensures a stable and reliable power supply, especially in areas where many electrical devices are operated simultaneously.

Areas of application for three-phase current

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

• Industrial motors and machinery
• Pumps, compressors and conveyor systems
• Household appliances such as electric stoves or heat pumps
• Workshops, craft businesses and construction equipment
• Energy distribution in cities and rural regions

Three-phase current also plays a central role in modern energy generation systems. Even renewable energies such as wind and hydropower usually generate three-phase current directly, which is then fed into the public grid.

Conclusion

Three-phase current, also known as three-phase alternating current, has become an integral part of the modern world. Due 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 efficiently transmitting energy via lines – three-phase current works reliably and powerfully. This is why this system forms the basis of modern electrical power supply and will continue to play a central role in energy distribution in the future.