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Reply To: Transformer riddle No.11 – Yyn0 Transformer

#1418
Hamid

    a-Yes b-Generally no, with regard existing overhead line you can benefit from some advantages of this connection. 1- The zero-sequence impedance of a star winding will be very high if no delta winding is present. The actual value will depend on whether there is a low reluctance return path for the third-harmonic flux. For three-limb designs without a delta, where the return-flux path is through the air, the determining feature is usually the tank, and possibly the core support framework, where this flux creates a circulating current around the tank and/or core framework. The impedance of such winding arrangements is likely to be in the order of 75 to 200% of the positive-sequence impedance between primary and secondary windings. For five-limb cores and three-phase banks of single-phase units, the zero-sequence impedance will be the magnetizing impedance for the core configuration. Should a delta winding exist, then the third harmonic flux will create a circulating current around the delta, and the zero-sequence impedance is determined by the leakage field between the star and the delta windings. Five-limb transformers have their zero-sequence impedances substantially equal to their positive-sequence impedance between the relative star and delta windings. 2-Zero Sequence Circuit Modeling of Yyn0 and Dyn0 connection is very different as you see below: 3-According to above diagram, the Yyn0 connection is provide interconnection path for zero sequence current between two sides of transformer. Therefore each side zero sequence impedance (high impedance probably) can be transfer to opposite side via power transformer and that mentioned software can calculate them. 4- The most common characteristics of three-phase transformer connection grounded wye