Delta Connection

On the Picture 1 is shown classic Delta (D) connection of the three-phase load. The connection of the three-phase load, as drawn on the picture, forms a triangle. The loads on the picture are marked as R1, R2 and R3, assuming that they are pure resistance loads. In general, the loads are more complex, so, they should be represented as impedances Z1, Z2 and Z3.

Picture 1: Delta (D) Connection of the three-phase load


The line voltage Ul is voltage between each two phases, Urs, Ust, Urt. Here, the currents that flows through each phase, are not equal with the currents that flows through each part of the three-phase load, R1, R2 or R3. From the other side, the voltage of the each part of the load is equal to the line voltage, Ul = Uf. Only in case when the three-phase load is symmetric, which means that all three resistances are equal R1 = R2 = R3 or all three impedances are equal Z1 = Z2 = Z3, then the line current Il (which flows through each phase Ir = Is = It = Il) is equal to the current which flows through the load If (Ir1 = Ir2 = Ir3 = If) times square root of 3, as shown on Picture 1.

Picture 2: Delta (D) Connection of the three-phase source


On the Picture 2 is shown Delta (D) connection of the three-phase source. The coils of the source are connected in delta configuration. Each node of the triangle formed with the coils provides one phase, as shown on the Picture 2, node 1 provides phase L1, node 3 provides phase L2 and node 2 provides phase L3. Here, there is no null line, therefore on the picture are shown only line voltages (Ul1,l2 ; Ul2,l3 ; Ul3,l1).

Also, as we mentioned for the star connection, the labeling of the phases on the Picture 1 is R-S-T, and the labeling of the phases on the Picture 2 is L1-L2-L3. In practice and in the literature we can find both of them, depending of the convention, however, they refer to the same phases. In other words, Phase R corresponds to the Phase L1 and both of them refer to the Phase 1 of the three-phase system. Phase S corresponds to the Phase L2 and both of them refer to the Phase 2. Phase T corresponds to the Phase L3 and both of them refer to the Phase 3.