The delta connection is a classic type of circuit in electrical engineering, which is mainly used in three-phase systems and in electrical power distribution. Three loads are connected in such a way that they form a closed delta – hence the name. In contrast to the star connection, no neutral conductor is required for the delta connection.
In the delta connection, one end of each coil (or other load) is connected to the beginning of the next, creating three electrical paths arranged in the shape of a triangle. The three outer conductors (L1, L2, L3) of the three-phase systemare connected to the corners of the triangle.
This type of connection results in the voltage of the outer conductors being present between the loads – the so-called phase voltage. In this case, the phase voltage corresponds to the phase voltage, as one load is connected directly between two phase conductors .
Compared to the star connection, the delta connection differs primarily in its type of connection and electrical behavior. In the star connection, the three loads are connected to a common point, the so-called star point. A neutral conductor often leads from this point to earth or to single-phase loads. This provides a defined reference voltage in the star connection and allows both three-phase and single-phase systems to be operated.
An important difference lies in the voltages that occur. In the star connection, the phase voltage is present at each load, i.e. the voltage between an outer conductor and the star point. The phase-to-phase voltage, i.e. the voltage between two phases, is greater than the phase-to-phase voltage by a factor of √3. This relationship can be expressed mathematically using the cdot operator:
ULeiter=3⋅UStrangU_{Leiter} = sqrt{3} cdot U_{Strang}ULeiter=3⋅UStrang
In the delta connection, on the other hand, each load is connected directly between two phase conductors. The voltages applied here are therefore the conductor voltages, and these correspond exactly to the voltage across the respective load – the phase voltage in the delta connection is therefore equal to the conductor voltage. There is no neutral conductor or star point in this connection.
The delta connection is preferred when high power is to be transmitted or when connecting electrical machines such as three-phase motors. As no neutral conductor is required, it is particularly popular in industrial systems in which the connected consumers represent a symmetrical load.
Another advantage lies in the higher possible power yield: For the same voltage and current, a motor in the delta connection can absorb a factor of 3 more power than in the star connection, which is particularly noticeable when starting large machines.
In a delta connection, the voltages between the phases act directly on the connected loads. This means that each load receives the full voltage between two phase conductors. The load on the conductors depends on the type of load and its electricalresistance or impedance.
Particular care must be taken with unbalanced loads or in the event of a fault, as there is no neutral conductor in the delta connection via which possible residual currents could be discharged – unlike in the star connection with an earthed star point.
Typical applications of the delta connection can be found in:
The delta connection is often combined with the star connection, e.g. in the so-called star-delta starting of motors. Here, a motor is initially operated in star connection to limit the starting currents and then switched to delta connection after a short time to achieve full power.
The delta connection is an efficient and powerful type of connection in electrical engineering that is used particularly in three-phase systems with high loads. Compared to the star connection, it offers a higher energy yield, but does not require a neutral conductor and places higher demands on the symmetry of the loads.
A sound understanding of the relationships between voltage, phase voltage, phases, loads and connection types such as delta or star is crucial for the safe planning and operation of electrical systems in the AC grid.
Discover more products
+49 (0) 60 62 - 9 42 50 
info@bre-trafo.com