Power transformer connections Delta

If a delta/wye connected power transformer is installed between the power source and the load, the power factor at the transformer input generally will reflect the average PF of the loads on the secondary. This conclusion works on the assumption that the low PF is caused by inductive and capacitive reactances in the loads. However, if the load current is rich in harmonics from rectifiers and switching regulators, some of the harmonic currents will flow no farther toward the power source than the transformer delta winding. The third harmonic and multiples of three will flow in the delta winding and will be significantly reduced in amplitude. By this means, the transformer will provide some improvement in the PF of the total load. 

Power distribution circuits suppHed from a wye-wye bank often create series disturbances in communication circuits (e.g., telephone interference) in their immediate vicinity. However, one of the advantages of this connection is that when a system has changed delta to a four-wire wye to increase system capacity, existing transformers can be used. 

Delta-connected system A 3-phase power distribution system where a single-phase output can be derived from each of the adjacent pairs of an equilateral triangle formed by the service drop transformer secondary windings. 

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