Date of Award

1-1-2010

Document Type

Campus Access Dissertation

Department

Electrical Engineering

First Advisor

Roger A. Dougal

Abstract

This dissertation focuses on the application of fault current limiters (FCLs) in power systems. The formula for the maximum first-peak fault current is derived to assist in specifying inductive FCLs. The specification process can be used to design and select proper FCL devices in a particular power system. What follows is the application of inductive FCLs to generator soft-synchronization, in which the inrush current and the oscillation of the frequency are limited under the faulty synchronization process. The transient stability of power systems is enhanced and the allowable range of voltage-angle differences is expanded during synchronization. The optimal placement of FCLs in a power system with a ring structure is also proposed. With this optimal placement, fault currents in any location can be limited, while the maximum capacity of the power source is maintained during the fault. The power quality at un-faulty busses is increased because the voltage sag is reduced. The proposed placement is verified by simulations with both resistive FCLs and inductive FCLs. Finally, a novel dual-FCL connection is introduced and applied to new distributed generations (DGs) connected to the existing power grid. This connection does not alter the protection relay scheme of the existing power grid. Also, the introduction of the dual-FCL connection eliminates the need to upgrade the circuit breakers at the feeder of the bus connected to the new DG. A dual-FCL controller determines the fault location and then trips the appropriate FCL device. In this connection, it costs one more FCL to enhance the synchronism between the new DG and the existing power grid. The voltage sag at the bus connected to the new DG is eliminated.

All analyses are verified by simulation tests in Virtual Test Bed (VTB). The VTB schematic consists of dynamic models of electric components, such as resistive and inductive FCLs, turbine generators with automatic synchronization, and circuit breakers. This schematic is utilized to demonstrate the transient performance of electric power systems during faults.

This dissertation is motivated by the potential for dangerously high fault currents. With the increasing demand for power in utilities and the development of independent power producers, electric power systems have become bigger and the potential for dangerously high fault currents has increased. To deal with this problem, fault current limiters are applied to compensate for the insufficient fault current interrupting capacity of circuit breakers and increase the reliability of the whole system. The emergence of novel superconducting materials, solid-state devices, and novel power electronics topologies in the past few decades has led to the investigation of FCLs with high-voltage and high-current ratings by institutes and companies around the world. It is possible to widely apply FCLs into the existing utilities with new distributed generation and isolated power systems.

Rights

© 2010, Yucheng Zhang

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