A review on protection issues in micro-grids embedded with distribution generations

© 2017 IEEE. According to recent developments, the application of distributed generations (DGs) has become popular especially in distribution systems. The high utilization of distributed generating resources in modern power systems can cause new challenges from protection coordination perspectives. Changing the distribution system structure from single-supply radial system to multi-source ring network, leads to the bidirectional power flow and also has a vital impact on protection coordination issues. In addition, micro-grids can be operated under grid-connected as well as islanded mode, and fault current is extensively different for these two operation modes. Therefore, traditional protection algorithms cannot be used in the advancement of power systems. In recent years, several research studies have been conducted to investigate the improvement of protection schemes in micro-grids. This paper presents a comprehensive review on protection problems resulting from micro-grids embedded with DGs, and discusses some alternate protection strategies

Lifetime evaluation of HV transformers

© 2017 IEEE. Power transformers are one of the most important equipment in power substations and distribution systems. As its price is about 55% of the whole substation price, it can be called the valuable element in the power grid. Thus, the lifetime management based on economical and technical indexes is highly essential for facilitating asset management and achieving higher reliability in the power system. This study presents the factors that can affect ageing transformers and analyzes oil test parameters. Dissolved gas analysis (DGA) is performed and some existing methods for evaluating of transformer operation based on DGA are compared. The pros and cons of each method are shown and a simple method to assess transformer condition is found. Also, three power transformers with real values and oil samples are studied for lifetime evaluation, and some possible solutions are proposed for better operation and maintenance

Impact of using current limiting reactor on the existing circuit breakers in micro-grids

© 2017 IEEE. Recently, distributed generations (DGs) have been widely used in distribution networks. Using DGs in the grid-connected mode leads to increase of the fault current level. This increase can affect the existing equipment especially circuit breakers (CBs) and operation of overcurrent relays. Current limiting reactor (CLR) has been proposed to reduce the effect of micro-grids (MGs) on the existing protection scheme during fault conditions by many researchers. However, there are some factors for interrupting the current by CBs which do not only depend on the fault current magnitude. Transient recovery voltage (TRV) and rate of rise recovery voltage (RRRV) can also affect the operation of CBs. This paper presents the equivalent analysis of the TRV and RRRV across a CB connected with a CLR. The transient stability is studied through simulation of a practical network, which shows the impact of using CLRs on the burden of CBs. In addition, some possible solutions are studied in this paper