Effect of the presence of distributed generation on the studies of overcurrent protection coordination

The presence of day by day more distributed generators connected at distribution levels, modifies the behavior of the protection system under short-circuit conditions in aspects such as: initial magnitude of the fault current, temporary variation of the fault current magnitude, and fault current flow direction. The study was made in analytic and experimental form, using MATLAB Simulink and equipment of a teaching laboratory. The overcurrent protection coordination study is carried out more based on the concept of specific energy as time function I²t (t) rather than based on the time-current characteristics I (t). The penetration values can be identified, for which it is necessary to use the methodology based on specific energy. It is concluded that the method using specific energy is something more laborious but it allows making the coordination study in precise form.