Product safety testing using induced corona detection

Experiments described in this paper show corona initiated between a transformer windings using a hi-pot tester set to AC voltage output, detected with both a spectrum analyzer and a small magnetic loop and with an audio microphone. To the power transmission industry, corona is a cause of power loss and is an interference nuisance for control and communication electronics. It is understood that dielectric-voltage withstand testing (electric strength testing, or hi-pot testing) is the industry norm for determining the adequacy of insulation systems in most electrical products. However, the potential to supplement dielectric-voltage withstand testing with corona testing, perhaps as a tool for mitigation of failures, is explored. For reliable operation in a smart-grid environment, all power transformers not only should have dielectric withstanding capability, but also should not produce corona. But can corona detection be used as alternate or supplemental tool for testing insulation strength, such as for high voltage transformers that might be found in smart-grid applications, perhaps as a tool for mitigation of dielectric breakdown failures? This paper explains the phenomenon of corona, presents experiments performed for detecting induced corona, and discusses potential benefits for corona detecting in insulating materials.