Ferroresonant overvoltages associated with utility interconnection of independent power producers

Abstract

The author discusses overvoltage and ferroresonance problems created when a cogenerator or other interconnected customer-owned generator is isolated (islanded) with a part of the utility system. These problems, and their mitigation and/or elimination, in large part determine the protective relaying and other technical requirements imposed by utilities on the customers who wish to interconnect generators to the utility system. The author discusses the types and sizes of the generators, the type and magnitude of the load, and how each affects the probability and relative severity of the ferroresonant overvoltages predicted. It is demonstrated that a section of the utility system can become islanded, or isolated from the utility source. The island is shown to contain a source of electrical energy (i.e. generator) which is greater in capacity than one third of the islanded load. The island contains a source of capacitive volt-amperes greater than the inductive requirements of the load and minimum excitation requirements of the generator(s), and less than five times the generator rating. The island contains one or more transformers. It is concluded that the best way to protect interconnected customer generators and the connected load from ferroresonance is to prevent or preclude the occurrence of these conditions.<>