Minimizing insulation failure damage: Progress in life test protection schemes

Learning why a stator insulation system fails often depends on de-energizing the test as soon as possible after failure begins. Any burning or arcing which occurs beyond the failure initiation simply destroys evidence needed to determine the cause of failure. Over many years we have incorporated maximum current, ground protection and over temperature controls into our life test facilities in an effort to prevent major destruction of a hermetic stator when it fails. These devices are described and their strengths and weaknesses discussed. This analysis led to the development of a new failure detection device named the Radio Frequency Failure Detector. The failure of an insulation is always accompanied by more or less arcing which generates radio frequency energy. A system sensitive to this can be used to disconnect the power at the moment a failure starts. This system is discussed in detail. The detector is very effective and has resulted in new insights into how stators fail.