Consequences of fault currents contributed by distributed generation

The demand of electric power is expected to grow sharply over the next twenty years. The department of energy (DOE) has a strategic plan that the twenty percent of new installed generation capacity should be from distributed generation (DG) by year 2020. This will result in the proliferation of DG in power systems.{09}Although there are many advantages of installing DGs, a few operating conflicts cannot be ignored. The appearance of cogeneration, DG, and unconventional generation may result in unavoidable consequences, such as increased of fault currents, losing coordination of protection system and safety degradation.; This dissertation focuses on the consequences of installing DG especially the increase of fault current. Fault analysis of the system with synchronous generators by applying conventional techniques is well studied. However, conventional techniques may not be appropriate to solve the problem when the system incorporates inverter based generation. A model of inverter based DG is proposed and applied as one of the tools for analyzing the system with inverter based DGs. A fault current estimation technique can be utilized as an online assessment of the fault current.{09}A new index called "ACF" (for "average change of fault current" after DG installations) is proposed as a new system-wide measure of the change in fault current in the system. An estimation technique is also proposed to calculate the ACF value of a system.; The economic impacts imposed by increased fault current due to the addition of DGs are discussed. Case studies show that the generation of the merchant plants under the fault current level constraint may result in higher cost of operation than the operation without this constraint.; Circuit breaker capability and setting of protective relays that were previously designed for the system without DGs may not safely and appropriately coordinate to manage faults. Artificial ant colony optimization techniques are proposed to determine the optimal coordination of the protective relays. The technique is applicable to both systems with or without DGs.