Surge diverter and transformer nonlinearities in z-transform electromagnetic transient analysis in power systems

The paper reports developments by which the nonlinear characteristics of surge diverters may be represented in z-transform methods of electromagnetic transient analysis in power-transmission networks. For this purpose, it is shown how surge-diverter equations may be combined with those for network nodes to which surge diverters are connected and solved using a Newton-Raphson sequence. As surge-diverter protection is often associated with transformers, the analysis scheme is then extended to include the nonlinearities of transformer magnetisation characteristics. The analysis method developed is a general and comprehensive one. Within a multinode network formulation, it provides for surge-diverter connections to any number of network nodes, and it allows for any number of transformer branches. In these terms, the work of the paper further advances the recently developed forms of electromagnetic transient analysis in power systems based on the z-transform.