ENGINEERING ARTICLES

A three-phase transformer bank can be easily created by using three single-phase transformers. The two sides of these three transformers can be either connected in a wye or a delta configuration, thus allowing four possible types of connections. These are: • WYE WYE: With the wye-wye (Y-Y) connection, the secondary side is in phase with the primary circuit, and the ratio of primary to secondary voltage is the same as the ratio of turns in each of the phases. A possible connection is shown in Figure 1. Power distribution circuits supplied from a wye-wye bank often create series disturbances in communication circuits (e.g., telephone interference) in their immediate vicinity. One of the advantages of this connection is that when a system is changed from a delta to a four-wire wye to increase system capacity, existing transformers can be used. Figure 1 Y-Y transformer with 0° phase shift between the primary and the secondary sides.  • WYE-DELTA: In the Y-Δ connec...

1) DELTA DELTA CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire service with a mid-tap ground. 2) DELTA WYE CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire grounded service with X O  grounded. 3. With X O  grounded, the transformer acts as a ground source for the secondary system. 4. Fundamental and harmonic frequency zero-sequence currents in the secondary lines supplied by the transformer do not flow in the primary lines. Instead the zero sequence currents circulate in the closed delta primary windings. 5. When supplied from an effectively grounded primary system does not see load unbalances and ground faults in the secondary system. 3) WYE DELTA CONNECTION 1. Suitable for both un-grounded and effectively grounded sources. 2. Suitable for a three-wire service or a four-wire delta service ...