Delta and Star Connections

in electrical engineering, methods of connecting the components of electric circuits in such a way that the three branches of the circuit form, respectively, the Greek letter delta and a star (Figure 1). Delta and star connections are used most commonly in three-phase circuits. The choice between a delta or a star connection is dictated by the operating conditions of the circuit. For instance, if the windings of a generator are joined through a star connection, fewer turns will be required than with a delta connection, but the conductor will need a larger cross section. Hence, while star connections are more advantageous at high voltages (the windings can be designed for voltages that are times lower than line voltages), delta connections are preferred for heavy generator load currents.

Figure 1. Connections: (a) delta, (b) star; (Z) impedance of the circuit segment, (i) complex currents, and (É) complex electromotive forces

Practical calculations are often simplified by substituting a star connection for an equivalent delta connection, and vice versa, without any change in the operating conditions of the external circuit. Here, the parameters of the elements of the equivalent circuit are calculated from known formulas.