Date of Award

January 2021

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Electrical Engineering

First Advisor

Hossein Salehfar

Abstract

Many countries and regions of the world are planning to reduce the energy sector's carbon footprint and increase sustainable energy sources. To this end, wind power has become one of their primary renewable energy sources. However, wind power's significant challenges relate to the need for long transmission lines that connect the offshore wind power plants to the onshore grid. The three major transmission configurations and design topologies of High Voltage AC (HVAC) Transmission, High Voltage DC (HVDC) Transmission, and Low-Frequency AC (LFAC) Transmission for offshore wind power resources have been thoroughly discussed both in industry and academia. HVAC is the standard transmission system for short and long distances. In contrast, HVDC is a popular solution for the long-distance transmission of offshore wind power generators. In recent years, LFAC transmission topology at 20Hz has become an alternative solution to HVAC and HVDC transmission systems. The significant advantages of LFAC transmission are the substantial increment of transmissible power over traditional AC transmission systems and the elimination of offshore converter stations. The absence of an offshore converter system renders LFAC transmission less costly compare to the HVDC system. The efficient design and reliability of offshore wind power transmission topologies are essential requirements for the transmission grid's smooth operation. This thesis work extensively investigated and reviewed the LFAC transmission topologies over HVAC and HVDC transmissions topologies of offshore wind power plans. Different methods are used to assess the reliability performance of system designs. In this research, the state of the art of the simulation models for three transmission systems have been developed for reliability analysis of the above three transmission systems topologies using Fault tree analysis (FTA). This research has identified several reliability performance characteristics including minimal cut sets, importance measures, and time-based matrics (i.e, number of failures and mean unavailability) of the transmission systems, and compared these characteristics among three transmission systems. For reliability performance analysis, the time-base metrics, such as mean-unavailability and number of failures of the systems over 10,000 hours of operation, importance measures, or reliability importance measures, such as Critical Importance Measure (CIM) and Risk Reduction Worth (RRW), and Cut Sets have been calculated. The thesis has successfully identified major fault events for all the three transmission systems, and that the large switch is the most critical piece of equipment in the HVAC system, while the AC/DC or DC/AC converter is the most critical piece of equipment in the HVDC system, and the DC/AC converter and Cycloconverter are the most critical components in the LFAC transmission system. Furthermore, to enhance the offshore transmission systems reliability and ensure their smooth operation, effective and reliable offshore wind power generation predictions are critical. To this end, this research work also introduces the necessary offshore wind power forecasting tools.

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