This paper presents the results of the simulations and their respective analyses corresponding to the power frequency overvoltages resulting from various fault types occurring inside a microgrid. During the islanded mode of operation, the analysed microgrid can be simultaneously fed by a diesel generator, a 1 MW wind power turbine, a small solar system and a 1 MW hydroelectric scheme. The operating voltage of the microgrid is 2.4 kV. During a fault in the system, the overvoltages normally occur in two remarkable instants. The first one occurs at the beginning of the fault itself. The second one occurs at the instant when the fault is cleared. The major concern here is the overvoltage during the fault period. Due to the travelling wave effect along cables and overhead lines composing the microgrid system, these overvoltages can be amplified, thus jeopardizing the insulation level of the microgrid transmission system and related equipment. Much of the work available now is dedicated to overvoltages present in high-voltage systems leaving a gap for the study and behaviour on low voltage microgrid systems. The overvoltage stress is characterized by the maximum low-frequency, short-duration (crest value) of the overvoltage. Both cables and overhead lines that constitute the microgrid transmission system are characterized by their R-L-C parameters. The simulations of the microgrid system are conducted using the ATP program. According to the international ANSI and IEEE standards, the minimum BIL (Basic Impulse Insulation Level) and BSL (Basic Impulse Switching Level) for the 2.4 kV voltage level are 20 kV and 10 kV, respectively; thus, care should be taken so that the healthy phases upon which commonly appear such overvoltages are not exceeded in their insulation level.
The objective of this article is to present a comparative evaluation and analysis related to the possible application of the main incentive policies, particularly net metering and feed-in tariffs, into microgrid systems. This is done in order to promote their implementation, expansion and consequent integration to medium and low voltage systems. To complement the study carried out, it was deemed essential including the response of the simulations related to the performance of a microgrid during its islanding (pre-planned and unintentional) process from the network. Today, the expectation about the performance of microgrid systems is high, especially if it is considered that its nearest ally, the smart grid technology, is having a rapid development. From the simulations conducted to assess the microgrid dynamic response, it became clear that microgrid systems may face some difficulties including unsuccessful attempts during the islanding process from the network.
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