Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Electrical Engineering

First Advisor

Hossein Salehfar

Second Advisor

Michael Mann


Over-currents are known to be the dominant cause of power system component failures or deterioration from full functionality. Some of these effects may remain unknown and could later result in catastrophic failures of the entire or large portions of the system. There are plenty of devices/methods available to limit the undesirable consequences of the over-current events. These devices/methods have great impact on system reliability by reducing stress on power system components and increasing their useful lifetime. Due to the importance of the subject, there is tremendous need to analyze and compare these devices/methods in terms of reliability. However, few researches have been reported on analyzing reliability impacts of these devices. Reported studies, in the meantime, appear to have investigated these effects qualitatively rather than quantitatively. This is mainly due to lack of a mathematical model to study the direct impacts of over-current values on system reliability. The main stream of reliability calculations are normally based on statistical measures of system outages rather than electrical parameters such as over-current values.

Over-currents usually appear in two common forms of fault currents and overload currents. Fault Current Limiters (FCL) and protection devices are commonly used to limit the impact of fault currents. FCL’s limit the magnitude of fault currents and protection devices limit the exposure time of the component to the fault current and therefore have great impact on increasing the lifetime of the components. Overloads, on the other hand, have smaller magnitudes than those of fault currents but can still be destructive because of normally much longer exposure times. Overcoming overload problems usually requires control strategies such as generation rescheduling, and/or load shedding, and optimized usage of existing assets. Using Demand Response (DR) programs are one of the most effective ways of reducing overload burdens on the power system.

In this dissertation, simulation models are developed and used to determine the effect of FCL on reducing the magnitude of fault currents. Various case studies will be performed to calculate the effectiveness of FCL’s in real power system applications. Then, security/dependability studies on the protection systems will be performed to analyze and calculate their effectiveness in reducing exposure times to fault currents. Based on the calculated indices, proper selection of protection schemes can be made based on the desired level of dependability/security.

In the next part of the work, a mathematical model is developed to calculate the effect of fault current magnitude and duration on the reliability and asset management. Using the developed model and results of the earlier sections of this research work, the impact of protection systems and FCL devices on reliability and asset management programs are quantitatively calculated and compared. The results from such studies will assist in maintenance planning and in proper selection of the fault current limiting devices with regards to desired reliability and asset management programs.

DR programs are introduced and modeled in this dissertation as an effective tool in reducing overload burdens on power system components. Using the developed mathematical model, DR programs are studied and compared in terms of reliability improvement that they provide by preventing unnecessary increase in the component failure rates.