**8. Conclusions**

Proper design and operation of present-day power systems and apparatuses each time require accurate simulations of their electromagnetic transient performance. An important aspect of these simulations is the realistic representation of transmission lines by digital computer models. The ULM is the most general line model available today, mostly with EMTP–type programs. By being of relatively recent creation, this model still is a subject for substantial improvements in accuracy, stability and computational efficiency. It has been postulated in this work that, both, researchers and power system analysts will benefit considerably from the full understanding of the theoretical basis of the ULM, as well as from counting with a ULM–type code that is easy to understand and modify. It has been contended also that the best way to carry out ULM research and development is by providing a model version in an interpretive environment and Matlab has been the platform chosen for this. This chapter provides a comprehensive description of the theoretical basis of ULM, phase domain line model. In addition to this, full description of a ULM prototype in Matlab has been provided here, along with executable code and typical application examples.
