Study on lightning impulse test waveform for UHV-class electric power equipment.

At present, a study is being conducted on the lightning impulse (LI) voltage test standard for UHV-class electric power equipment at WG 19 "Adaptation of TC 42 standards to UHV test requirements" in IEC TC42 "High-voltage and high-current test techniques". In the present paper, the past LI voltage test results for UHV-class equipment were initially investigated to determine test waveforms that could be generated. As a result, for a UHV-class transformer and gas insulated switchgear assembly, the front time T1 exceeded 2.2 μs or more, or even considerably 3.0 μs in some cases in order to generate a waveform with an overshoot rate β' of 10% or less using existing test facilities. Subsequently, experiments were conducted with regard to the extension of the T1, which is a prospective way to revise the LI voltage test waveform. Breakdown characteristics with respect to the T11 were measured using the largest possible models assuming UHV-class equipment for three types of insulating media, namely an SF6 gas gap, an oil gap, and a long air gap. Consequently, it was confirmed that extending the T1 up to about 3.6 μs had a minor influence on the breakdown characteristics. In addition, a study was also conducted on the influence of the deregulation of the standard value for the T1 from a viewpoint of insulation properties of equipment for the wave front steepness. As a result, it was concluded that the equipment insulation performance could be appropriately verified even if waveforms with an extended T1 were used. Based on these data, the idea of the standard for lightning impulse test waveforms for UHV-class equipment was proposed as follows: The standard voltage waveform shall be the same as the conventional one for less-than-800 kV equipment with a T1 of 1.2 μs and a time to half value of 50 μs but the upper allowable range of the T1 may be up to 3.6 μs; provided, however, that a note shall be added besides the exceptional provision that, whenever possible, the test should be conducted using a waveform of which the T1 is adjusted to 1.56 μs or less, the same as that for less-than-800 kV equipment. [ABSTRACT FROM PUBLISHER]