ABSTRACT
Transformers experience external short-circuit events during service, and understanding their behaviors during such events is key to building robust units. After this chapter introduces characteristics of short-circuit currents, related axial and radial forces and their relations with winding geometry are estimated. Failure modes are presented, including performances of special units such as radial or axial split windings. Secondly, current calculations under different types of short-circuit, such as three phases to ground, single phase to ground, phase to phase and two phases to ground are listed, accompanied with calculation examples. Third, effects of transformer impedance and external neutral impedance on the short-currents are discussed. The calculation of short circuit forces on winding leads is also given. Calculations of both radial and axial stresses on conductors, as well as limits are listed as checking tools. The measures for robust winding structure are summarized.
