Partial discharge detection method: UHF partial discharge detection technology

Electrical detection methods include pulse current method, radio interference voltage method, ultra-high frequency  (UHF)  partial discharge detection technology, and dielectric loss analysis method  . The most direct phenomenon of partial discharge

in electrical detection method   

is the charge transfer between electrodes. Each partial discharge is accompanied by a certain amount of charge passing through the dielectric, causing the voltage on the external electrode of the sample to change. In addition, each discharge process lasts for a very short time. In the air gap, a discharge process is  on the order of 10  ns,  and in the oil gap, a discharge time is only 1 ms.  According to Maxwell  's electromagnetic theory, such a short-duration discharge pulse will generate high-frequency electromagnetic signals that radiate outward. The partial discharge electrical detection  method is based on these two principles. Common detection methods include pulse current method, radio interference voltage method, dielectric loss analysis method, etc.  In particular,  the ultra-high frequency detection method proposed by Dr. S.  A.  Boggs  and Dr. G.  C.  Stone  in the 1980s  has received widespread attention in recent years. And practical products have gradually been introduced.  2.1.1  Pulse current method  . Ultra-high frequency  (UHF)  partial discharge detection technology  Before  the 1980s  , the operating frequency band of partial discharge detectors on the market was only  below 1 MHz. In 1982  , Boggs  and  Stone  increased the measurement frequency band of the test instrument to 1 GHz in their experiment  and successfully tested  the initial partial discharge pulse in GIS [5].  In this frequency band, the noise signal is drastically attenuated, which can effectively achieve noise suppression and reproduce the partial discharge pulse almost losslessly , thus  deepening the research on the mechanism of partial discharge. UHF detection is divided into UHF narrowband detection and UHF ultra-wideband detection. The former has a center frequency  above 500MHz and a bandwidth of more than ten MHz  or tens of MHz.  The latter has a bandwidth of several GHz.  UHF ultra-wideband detection technology has the advantages of high noise suppression ratio and  more information, which has attracted people's attention. The so-called UHF  detection technology usually refers to UHF ultra-wideband detection. The sensors used for UHF partial discharge detection are mainly microstrip and antenna sensors. Using microstrip antennas as sensors,  Kurtz  et al. proposed as early as 1980 that the sensors they designed were used for partial  discharge  testing of large motors. They were installed on one or two magnetic poles to detect the discharge of a single stator bar. At present, microstrip antenna sensors have been used in the detection of  partial discharge of large power transformers, GIS, power cables and other equipment.  For partial discharge detection of large motors, H.  G.  Sedding  et al.  proposed a stator slot coupler  in  1991.  The  sensor consists of a ground plane strip induction conductor and coaxial output cables at both ends  Its coupling mode is neither inductive nor capacitive, but has the nature of distributed parameters. Therefore, it has a very  wide frequency band and can reflect the difference in waveform between internal discharge and external interference.