Star connection

The star connection is a frequently used connection type in electrical engineering, especially for three-phase applications. It is characterized by a star-shaped arrangement of the phases, in which the loads are connected to a common point, the so-called star point. This electrical circuit enables a stable distribution of voltage, current and power and is often used in power distribution and transformers.

As a fundamental concept of three-phase technology, the star connection plays an important role in the construction of modern power grids. Due to its structure with outer conductors and a neutral conductor, it can be used for both symmetrical and asymmetrical loads. Particularly in power supply networks and industrial systems, this type of connection ensures that electrical energy is distributed efficiently and different consumers can be operated reliably.

Structure and function of the star connection

In the star connection, three phase conductors are each connected to one end of a load. The other ends of all three loads are brought together at the common neutral conductor, also known as the star point. This results in a star-shaped topology. Each load is located between a phase conductor and the neutral conductor. The voltages applied to these loads are referred to as phase voltages.

Between two phase conductors is the so-called conductor voltage, which is greater than the phase voltage. The following relationship applies:

U_L = sqrt{3} cdot U_S

ULU_LUL stands for the conductor voltage and USU_SUS for the phase voltage. The symbol “cdot” stands for the multiplication. In a symmetrical star connection, the phase voltages are the same, as are the phase currents, if the resistances of the individual loads are identical.

A practical example can be found in the European electricity grid. Here, the voltage between an outer conductor and the neutral conductor is typically 230 volts. In contrast, the conductor voltage between two outer conductors is around 400 volts. This difference is due to the out-of-phase voltages in the three-phase system, which are offset by 120 degrees to each other.

The neutral point is an important reference point for the entire system. A stable voltage reference can be established via the neutral conductor, which is particularly important when supplying single-phase loads.

Star connection vs. delta connection

In addition to the star connection, there is also the delta connection, in which the loads are connected in the form of a closed triangle. In contrast to the star connection, the connection points of the loads are connected directly to each other, creating an electrical delta. Both types of circuit are used in electrical circuits such as electric motors or transformers.

An important difference lies in the applied voltages and currents. In the delta connection, the phase voltage corresponds to the voltage at the load, whereas in the star connection, the phase voltage is applied to the load. With identical resistance per phase, the phase currents in the star connection are equal to the phase conductor currents.

Another difference can be seen in the current load of the individual lines. While the phase currents flow directly through the outer conductors in the star connection, the currents in the delta connection are distributed differently across the cables. These differences are particularly relevant when planning electrical systems and when dimensioning cables.

Current, voltage and resistors

The voltages, currents and resistances in the star connection can be easily calculated. With the same load – i.e. the same resistances in all phases – the current values are the same. In this case, we speak of a symmetrical load. The current in the neutral conductor is then zero, as the currents cancel each other out.

The level of the current depends on the respective resistance through which it flows. The lower the resistance, the higher the current. The value of the resistors in the individual strings is decisive for the current distribution in the grid.

However, if there are different resistances in the strings, this is referred to as an unbalanced load. In this case, a current flows via the neutral conductor, as the currents of the individual phases no longer balance each other out completely. The neutral conductor then takes on the task of compensating for the current differences between the phase conductors.

The calculation of current and voltage is therefore a central component in the planning of electrical systems. Engineers and technicians use these correlations to design stable networks and ensure a reliable power supply.

Transformation and application

The star connection plays a central role in the transformation of electrical energy. In energy supply, it is often used in conjunction with transformers to transport electrical energy efficiently over long distances. The star connection is particularly advantageous, as the same voltages can be realized for consumers and different voltage levels can be provided.

Another advantage is that single-phase loads can also be supplied via the neutral conductor. This makes the star connection particularly suitable for power grids in which both three-phase appliances and single-phase household appliances are operated.

The combination of star and delta connection means that motors can be operated in star mode first when starting up (lower current consumption). Many three-phase motors are initially operated in star when starting. In this operating state, a lower voltage is applied to the windings, which reduces the starting current. The motor is then often switched to delta connection so that full power and torque are available. Such solutions are typical for industrial use with three-phase current.

This type of connection is also frequently used in industrial automation and in large production facilities, as it enables stable and controllable power distribution.

Conclusion

The most important content relating to the star connection includes the structure with phase conductors, neutral conductors, resistors and the calculation of voltages and currents. The star connection offers a stable and safe way of distributing energy under the same connection conditions.

The interaction between conductor voltage, phase voltage and phase current is particularly important. These variables determine how electrical energy is distributed in the three-phase system and how loads can be connected.

Due to its versatility, it is used in both industrial and private networks and is one of the most important fundamentals in electrical engineering. Its applications range from simple electrical circuits to complex transformation systems and modern energy supply networks.