Mathematic Model and Operating Performance of YNvd Transformer

The YNvd transformer, which is one kind of three-phase three-winding balance transformer, has several properties and can be used in traction power system of electric railway. Based on the magnetomotive force balance equations, winding connection equations, output-port equations and voltage transfer equations, the mathematical model of the YNvd transformer is set up. The performance of transformer in different grounding mode is discussed. The two-phase equivalent circuit in secondary side is obtained with the source impedance of the power system taken into account. The short-circuit current calculation formulae are deduced when variety kinds of short-circuit failure appear in the traction power substation, and the voltage losses of bus bars are calculated. These studies have great significance on the application of YNvd transformer.