C37.34a-1978 - IEEE Standard Test Code for High-Voltage Air Switches, Corona Tests Supplement to ANSI/IEEE C37.34-1971
Description: Air switches do not have a radio-influence rating requirement, however, the proposed standards establish a definition of corona, develop the concept of corona-free voltage, establish the requirements for corona-free voltage, and criteria for acceptance. The corona-free voltage is specified to be 1.10 times the line-to-neutral voltage equivalent of rated maximum voltage. Only visible corona are defined because this satisfies the majority of user requirements. Actual tests performed show satisfactory radio influence voltage (RIV) levels after the extinction of visible corona over the external extremities of the device. In the past, switches determined to be corona-free by the human eye accustomed to a darkened area, have not been a source of radio or television interference. The standards, however, allow an alternate photographic corona test method where necessary. Tests require switches to be free of visible corona at the corona extinction voltage because this voltage is lower than corona starting voltage.