Overvoltage Condition Assessment of a Microgrid Due to Faults Occurring in the Islanded Mode of Operation

Abstract

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.

Investigation of Temporary Overvoltage on Microgrid with Emphasis on Ferroresonance

“…Ferroresonance occurs in an electric circuit containing nonlinear inductance, capacitance, low losses and voltage source, hence it is necessary to investigate ferroresonance on microgrid since all these elements are present. Some researchers have worked on overvoltage as regards to microgrid; Vasquez-Arnez, et al [4] worked on microgrid of PV system, wind power and hydroelectric and 1MW each by analyzing power frequency overvoltages rising from different types of faults ranging from line-to-ground to double line-to-ground during island mode. The result was compared to basic insulation level (BIL) of the system and the overvoltages were found not to be dangerous to the system as they were below BIL.…”

Micro-redes elétricas: estado da arte e contribuição para o dimensionamento, aplicação e comercialização da energia produzida.

“…Em um artigo recentemente submetido a um periódico internacional[101], foram analisadas às sobretensões que poderiam aparecer em uma MR produto de correntes de falta faseterra em uma MR ilhada. Para isso foi utilizada uma MR similar ao daFigura 5.10, exceto que neste caso foram removidas as cargas extras assim como inserida uma linha aérea, conforme mostrado na Figura 5.22.…”