Experience with field coil interconnection failures on large hydro generators Part I

Over the last several years, Ontario Power Generation has experienced multiple field coil interconnection failures on several different machines in the same power-house of the same manufacturer. There have been other instances of this type of failure at other powerhouses within OPG, all with the same common manufacturer. The rotor of a large hydro generator is often a forgotten component of the machine and at times, little effort is put into assessing the condition of this critical component other than a simple reactance test and a low voltage insulation resistance test. The paper will discuss the numerous failures experienced, site investigation, and the solution implemented for one of the stations.