Detection of stator winding insulation failures: On-line and off-line tests

Insulation faults in electrical rotating machines are a matter of great industrial interest since the economic losses associated with these events are usually equal or even higher than the cost of the machine itself. For this reason, the development of monitoring and diagnostic techniques to detect this failure during its earliest stages has been a subject of great interest. On the other hand, the accuracy of the quality controls applied to the manufacturing of insulation systems is an essential issue to reduce fault rate and increase machine life. The aim of this paper is to present a comprehensive review of the scientific literature in this field, including not only research papers but also existing standards for off-line tests. A critical review of their diagnosis capability, especially on low voltage machines, is essential to clarify the reliability of these techniques as well as the convenience of its generalized industrial use.