Centralized Fault Management Approach for the Protection of Smart Grids

Electrical Distribution Systems (EDS) in future are likely to be changed to looped structures with renewable energy and associated Power Electronic Devices (PED). The looped structures will not only enable the integration of local renewable energy generation, but also improve the efficiency and reliability of energy operation in the EDSs. However, the change of structures and the integration of PED devices also bring tremendous challenges to the design of the protection systems for the EDSs of the future. These EDSs are often referred to as smart grids. The first challenge comes from the change of structures. The looped structures will have significantly different dynamic behavior during fault conditions as compared to the traditional EDSs, which are normally in radial structures and supplied by a single source. The second challenge is the highly distorted fault current waveform and bi-directional power flow from the PEDs and the local renewable sources. The third challenge is the requirement of adaptability, the protection systems must be able to accommodate the dynamic operating conditions of smart grids with multiple controllable PEDs. The traditional protection approaches that are based on local relays may fundamentally facilitate the above challenges individually for smart grids with simple structures and operating features, but will not work for the smart grids with complex structures and operating features. Therefore, a more intelligent, rapid and adaptive protection system, which is capable of solving the challenges comprehensively, is needed for the smart grids. This is the major motivation for this dissertation. This research proposes a centralized fault management (CFM) approach as a generic protection solution to the smart grids. In contrast to the traditional protection approaches that are constrained by local relays, the CFM approach applies a new protection structure, which is composed of a digital data acquisition subsystem and a communication subsystem. In the new structure, multiple CFM systems are designed to manage a smart grid, and thus to provide protection redundancy and to ensure overall system reliability. The new structure is expected to enable the development of a new generation of protection technology, which will facilitate the rapid design and implementation of a highly adaptable protection approach for smart grids of both AC and DC types. The research into developing the proposed CFM approach consists of the following parts: 1. We propose a centralized fault management approach that considers all the three challenges for smart grids. The approach is based on zone division and the adapted percentage differential protection methods. It is highly adaptive to smart grids with different structures and operating conditions. It also minimizes the need for coordination of the different zones in a smart grid. 2. We characterize the communication requirements for the CFM approach. We improve the performance models by adding the CFM devices onto the models. Then we characterize the sensitivities and influence factors of the models in order to evaluate the performance of the CFM systems. 3. We develop a generic design guideline for the CFM approach to protection applications of other smart grids. We illustrate the design guideline by using a MVDC shipboard system. We implement a demonstration CFM system on hardware, and then test the CFM system on an RTDS Hardware-In-the-Loop (HIL) test-bed. The HIL test results show that the CFM system determines faults precisely and rapidly for a small smart grid with looped structure and multiple generators. We conduct simulations on a network simulator, i.e., the OPNET software, to validate the CFM models. The OPNET simulation results show that the models are accurate in analyzing the performances of the CFM systems. For the future work, we summarize some related topics, such as accurate modeling of the processing delay, hardware implementation of a full CFM system, full protection HIL testing for the MVDC system, and external control functions of the CFM program.