It is a well-known fact that many motor failures begin as turn-to-turn shorts
within a single winding. These turn-to-turn shorts then create hot spots which
in turn degrade the insulation in adjacent turns until the entire winding fails.
The mechanism of this type of failure may take a long time to develop depending
upon the operating characteristics of the motor. This type of failure or
degradation cannot be detected by the insulation resistance test (megohmmeter)
or high-potential testing because of its incipient nature; however, this
type of incipient type of fault can be detected by surge comparison testing.
Many types of faults may be detected by the use of surge testing, such as
turn-to turn, coil-to-coil, phase-to-phase as well as opens and grounds