delta connection
A type of three-phase connection.
delta connection: three phases in a loop, not a star
A delta connection, or delta winding, joins three power-supply phases in a closed triangle or loop rather than meeting at a neutral point. Each phase line connects to two of the three windings; current flows around the perimeter. The three line voltages are 120 degrees apart, and in a balanced system each phase voltage equals the line voltage, typically 400 V or 480 V in industrial settings.
The name comes from the Greek letter delta (Δ), which visually represents the triangular wiring diagram. The alternative is a star (or wye) connection, where all three phases meet at a central neutral point, and line voltage is 1.732 times phase voltage. Delta is favored where there is no neutral requirement and where line-to-line voltage is sufficient for the load.
Practical variants and limits
Three-phase motors, transformers, and generators can be wound and connected either way. A delta-connected motor draws larger phase currents than a star-connected motor at the same line voltage, because the phase voltage is higher. This makes delta motors run hotter at the same power output, but delta is common in high-power applications where the higher line voltage (and thus lower current for a given power) is an advantage elsewhere in the system.
One significant drawback is that there is no neutral conductor in pure delta, so single-phase loads cannot easily be served. A fourth wire can be derived by grounding one transformer center-point, creating a "corner-grounded" or "open-wye-delta" hybrid, but this asymmetry creates unbalanced currents. Industrial sites using delta supplies often install separate single-phase transformers or employ a wye-delta hybrid supply instead.
Fault current behavior differs in delta: a single phase-to-ground fault does not complete a return path through a neutral, so ground-fault relays must be set differently than in star circuits. Three-phase faults in delta systems are symmetrical and straightforward to analyze, but phase-to-phase or phase-to-ground events demand closer attention to earthing and protective devices.