Resumo:
The main goal of this dissertation is to provide the necessary technical knowledge for a complete and integrated analysis of the Over Current Protection of power electrical distribution networks with rated voltage less than 34.5 kV(median and low voltage). For this end, a methodology is presented based on information obtained from different national and international references that work with this theme or some topics of this work.
Before starting to present the philosophy and criteria utilized in the selection and coordination of different protection devices, it’s necessary a simple reviewing of basic concepts used in calculation of phase and sequence impedances and short circuit currents, considering distribution network composed by three-phase, two-phase, single-phase, overhead or underground lines, and also the different types of fault that usually occur in these electrical networks.
The equations and calculation methods shown are based on Fortescue Symmetrical Components, Carson Equations, Kron Reduction, Geometrical Mean Distances and Radius, Kirchhoff Laws, Thevenin Equivalent Circuits and Nodal Analysis.These impedance and current values can be also obtained from computer programs or directly from a conductor data table (Appendix A) during a protection system analysis; however, to know how these values are computed is very important.
Manufacturing and operating characteristics, and application factors of protection devices, such as circuit breakers, relays, automatic reclosers, sectionalizers and fuses are also introduced.
To conclude this work, the major criteria and some application examples of selection and coordination analysis of distribution systems over current protection are finally presented.
