Research On Detection Of Silicone Oil Level In High-voltage Cable Porcelain Bushings

With the rapid development of the power grid,the stability and operation safety of highvoltage cable porcelain bushing,an important insulation device in high-voltage equipment,should be ensured as a priority.Long-term experience of the hostile working environment may lead to leakage of silicone oil inside the porcelain bushing,which results in poor performance in heat dissipation and insulation.The Joule heat of the electrical equipment will accumulate inside the porcelain bushing,and eventually cause an explosion accident,which will jeopardize the safety of life and property.At present,the detection of silicone oil level in high-voltage cable porcelain bushings adopts the sampling mode.The manual visual inspection is performed after the cutting off the power and disassembling the porcelain bushing,which is extremely time consuming.The ultrasonic testing technology has the advantages of low cost,simple operation and high detection precision,and can directly,quickly and reliably detect the inner silicone oil level of the porcelain bushing.This paper selects the umbrella-shaped porcelain bushing as the research object,proposes a novel ultrasonic-based technique in detecting the silicone oil level in porcelain bushings.It has important research significance and engineering application value.The research was funded by the Guangdong Science and Technology Plan Project(2017010160646)and China Southern Power Grid Co.,Ltd.Science and Technology Project(GZM2015-1-0011).This paper is organized as follow:(1)The requirements of the detection of silicone oil level in porcelain bushing and the structural characteristics of the umbrella-shaped porcelain bushing were analysed.Considering the basic characteristics of the ultrasonic wave and its transmission,reflection and refraction phenomena,the propagation characteristics of the ultrasonic wave in the porcelain bushing was investigated.An ultrasonic-based silicone oil level detection system was proposed and the hardware and software are designed separately.(2)Several key modules of the silicone oil level testing instrument were designed according to its expected performance index.The ultrasonic transducer was designed according to the outer wall shape of the high-voltage cable porcelain bushing.The special delay block was designed according to simulation results of the finite element analysis experiment.A new coupling method for the ultrasonic transducer and the porcelain bushing was proposed.(3)A specialized wavelet threshold de-noising method for the ultrasonic echo signal of the silicone oil level detection was proposed.A specialized compensation algorithm for the ultrasonic detecting signal was presented,according to the continuously change of wall thickness of the porcelain bushing.The criterion of the silicone oil level detection was formed.The signal analysis and processing software on PC was designed in order to display and interpret the ultrasonic detecting signal and raise an alarm when necessary.(4)The porcelain bushing inner silicone oil level detecting platform is built up.Firstly,the silicone oil level detection at the upper or lower neck of the porcelain bushing is conducted,in order to determine if the silicone oil inside is completely full or drained.Secondly,the silicone oil level detection at the umbrella shaped area of the porcelain bushing is conducted,in order to determine the specific location of the silicone oil level.The signal analysis and processing software on PC is used to process the ultrasonic detection signal with the wavelet threshold denoising method mentioned above.The result proves that the ultrasonic-based silicone oil level detecting system successfully detects the silicone oil level in high-voltage cable porcelain bushings,and the detection error is less than 20 mm,which meets the actual requirement of the detection error within 50 mm.