DEVELOPMENT OF NOVEL FAULT DETECTION AND DIRECTION ESTIMATION SCHEMES FOR AC MICROGRID

Abstract

With the increasing population and industrialization, electricity demand is increasing day by day. The traditional way of electricity generation from limited non-renewable resources failed to meet this increasing electricity demand. Therefore, the application of renewable energy resources for electricity generation gains the attention of researchers. Microgrid integrates several distributed energy sources and loads that behave in relation to the grid as a single controllable entity and operate within predetermined electrical parameters. Microgrid encourages the addition of varied loads and sources of renewable energy types. Numerous benefits of MG include decreased transmission losses, minimal carbon emissions, and increased system dependability. This electricity is supplied to the end-user by a very complex transmission and distribution network. The network is equipped with different protection devices to keep the system protected from various unwanted scenarios such as line outages, unwanted tripping of the circuit breakers, bus faults, etc. Most conventional distribution protection is based on shortcircuit current sensing. The presence of DERs might change the magnitude and direction of fault currents and might lead to protection failures. Directly coupled rotating- machine-based micro sources will increase short-circuit currents, while power electronic interfaced micro sources can not normally provide any significant levels of short-circuit currents required. Some conventional overcurrent sensing devices will not even respond to this low level of overcurrent, and those that do respond will take many seconds to do so rather than the fraction of a second that is required. Thus, in many operating conditions of microgrids, problems related to selectivity (false, unnecessary tripping), sensitivity (undetected faults), and speed (delayed tripping) of protection systems may arise. Protection of microgrid has become challenging due to the hosting of various factors such as distributed generation, energy storage systems, information and communication technologies, etc. Due to the change in the operation method of the MG, the magnitude and direction of the fault current are also reversed, for which conventional overcurrent protection systems perform poorly. For the MG to operate reliably, the fault must be identified and fixed as soon as possible as it appears. The protection system must respond effectively to faults in the MG’s grid-supported and grid-isolated mode of operation. During the inter-grid operating mode, whenever faults occur in the primary grid, then the protecting devices should disconnect the MG from the primary grid to protect the critical loads, while during internal faults, the protection scheme should isolate the minimum faulty section of the MG to clear the fault. The classical protection scheme, such as fuse, recloser, and directional overcurrent relays used for fault protection, can’t be successfully implemented for MG protection. This research mainly focuses on the development of a novel fault detection & new directional element for microgrid, considering the problems associated with the commercial directional over current relays for protection. This research presents a comprehensive review of the available microgrid protection schemes which are based on traditional protection principles and emerging techniques that can detect the faults accurately. A categorical assessment of the reviewed protection schemes is also presented. Several case studies such as generator output change, high resistance fault, signals affected by noise, pole tripping, etc are utilized for analyzing the effectiveness of the proposed technique. To assess the effectiveness of the suggested methodology, several simulations are performed at different locations of the proposed modified IEEE 34 bus & IEEE 7 bus microgrid. Real-time experiments are conducted to verify the results. The system analyzed is a modified IEEE 7 & 34 bus MG test system, modeled in RTDS/RSCAD software, and the analysis is interpreted in the MATLAB platform. The novel technique performances are compared with several other preexisting detection & directional relaying algorithms, and the suggested methodologies have a significant degree of accuracy for detection and direction estimation.