This paper presents the results of the simulations and their respective analyses corresponding to\nthe power frequency overvoltages resulting from various fault types occurring inside a microgrid.\nDuring the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel\ngenerator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric\nscheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages\nnormally occur in two remarkable instants. The first one occurs at the beginning of the fault\nitself. The second one occurs at the instant when the fault is cleared. The major concern here is the\novervoltage during the fault period. Due to the travelling wave effect along cables and overhead\nlines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the\ninsulation level of the microgrid transmission system and related equipment. Much of the work\navailable now is dedicated to overvoltages present in high-voltage systems leaving a gap for the\nstudy and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by\nthe maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and\noverhead lines that constitute the microgrid transmission system are characterized by their R-L-C\nparameters. The simulations of the microgrid system are conducted using the ATP program. According\nto the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation\nLevel) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV,\nrespectively; thus, care should be taken so that the healthy phases upon which commonly appear\nsuch overvoltages are not exceeded in their insulation level.
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