| Gas insulated switchgears (GIS) have the advantages of covering the smaller area, running more safely and reliably, less constant-maintenance, overhauling in a longer period and so on, so it develops very quickly and gets more and more applications when it came out. Operation experiences show that intrinsic defects in GIS still cause accidents though its high reliability. Insulation breakdown is primary reason for GIS electrical failures. Partial discharge (PD) phenomena are most common characteristic before insulation breakdown in GIS. By PD on-line monitoring systems, GIS internal defects can be discovered in time to avoid the occurrence of fatal failure.On-line monitor of PD signals in GIS is a comprehensive research project, which relates to the theories and knowledge of many different areas. In this paper, based on microwave and antenna theory, electrical measurement method and digital signal processing and so on related theory, On-line detecting system of PD signals in GIS using dipole antenna sensor are developed, and wavelet technology of suppressing white noise and narrowband interference are systemically analyzed and deeply studied. Main researches and conclusions in the paper are as following:(1) Based on microwave and antenna theory, the traditional narrowband dipole antenna is changed to the ultra-wide frequency antenna according to line-antenna wide frequency technology. The antenna impedance match is very great because of using of unique impedance variation method. So an ultra-wide band and ultra-high frequency dipole antenna sensor using of PD detecting in GIS is successfully developed. The test compared the inner loop sensor with dipole antenna in the lab show that ultra-high frequency PD signals can be received by outer dipole antenna, and signals breadth is the bigger, frequency spectrum is the wider.(2) The analysis about transmission, attenuation and leakage characteristic excited by PD in GIS indicate that ultra-high frequency PD signals can transmit in GIS although a little attenuation. The leakage of electromagnetic waves will increase owing to supporting insulator, which provides advantages for detecting PD in GIS by ultra high frequency outer (UHF) sensor method.(3) The high performance amplifier and the half-distributing parameter UHF filter are designed. The performance of antenna sensor and the filter and amplifier are great and each frequency matches another, so demand of UHF signals detecting and signal pretreatment can be got.(4) Four PD high frequency simulative signal models are constructed. Compared with normal low frequency simulative models, the high frequency simulative signals are advantage to depressing PD noise, which proves more superiority of UHF method.(5) PD simulative signals and detecting data in the lab have been process by wavelet translate, and the influencing factor about depressing white noise have been comprehensively analyzed , which indicate that simulative signals can reflect real PD signals and wavelet translate can depress white noise, improve SNR.(6) Based on Wavelet translate, the principle and algorithm of Standard Deviation Threshold Method (STDM) has been put forward to reject the narrow band interference. Combined with hardware filter, soft-hard filter method has been brought forward to reject the narrow band interference.
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