Experiences of using simultaneous 3-phase voltage approach for dark (blackout) tests on high voltage stator windings as a quality control tool

One of the quality control methods to evaluate stator insulations, especially those for high voltage applications, is the so called dark (blackout) test. The main purpose of such test is to confirm whether those stator windings would be free of external discharges during normal operations. Dark test is typically done by placing stator winding in a totally darkened room with all visible lights blocked out. Test personnel, and customer witness if present, stay inside that dark room to inspect the stator winding for any possible discharge when some pre-determined test voltages are applied. Traditionally, such tests are done with one phase of stator winding energized at a time, assuming all 3 phases of that winding are not internally connected. However, such test method is rather time consuming, and does not represent true voltage interactions between different phases. Therefore, one of our customers specifies a 3-phases test requirement on many of their stator orders. This paper illustrates that different approach by using a custom built power source with 3-phases electric circuit to meet that specific requirement. With this set-up, 3-phase voltages are applied to the tested stator winding at the same time. It not only provides proper stator winding interactions between different phases that the customers have asked for, but also shortens the required test time significantly.