Three methods of measuring partial discharge in GIS cabinet1) Ultrasonic testing method
The ultrasonic detection method is based on the characteristics of ultrasonic waves generated during the partial discharge process, using ultrasonic sensors to collect the ultrasonic waves generated by partial discharges in the gaps of the switch cabinet wall, and thereby obtain the location and size of the partial discharges. This method can effectively avoid the influence of electromagnetic interference, the positioning is convenient, and the results of online and offline detection are basically the same. However, due to the complicated propagation process of ultrasonic waves in the switchgear and the existence of refraction, which seriously affects the accuracy of partial discharge positioning, it is impossible to use ultrasonic signals to quantitatively judge and identify partial discharges.
2) Light detection method
The light detection method is realized by detecting the light wave signal generated during the partial discharge process. The spectrum produced by partial discharge is generally between 3000-5000A, and its peak value is about 4000A. Since the photomultiplier tube can detect tiny light wave signals, it can be installed in the observation window of the switch cabinet shell, and sent to the acquisition and processing part by the cable after passing through the signal processing circuit. The biggest disadvantage of this method is that holes (1-2cm in diameter) must be made on the switchgear shell, and each compartment has at least one hole, so this method is difficult to apply in the field.
3) Infrared detection method
In the infrared detection method, the heat energy released during the partial discharge process will increase the temperature of the insulating partial discharge area, so as long as the temperature change area is determined, the position and extent of the partial discharge can be obtained. The infrared detection method uses an infrared camera to detect this tiny temperature, so as to obtain the degree and location of partial discharge. However, there are many factors that cause the temperature change of the insulating equipment, so the reliability of this method is poor.
To sum up, whether it is the temperature monitoring of the switchgear or the partial discharge monitoring, it only monitors a single quantity and cannot respond to the real-time situation in the switchgear in time. At the same time, neither of the two types of monitoring can achieve an early warning before a failure occurs, which is the biggest drawback of the two. Therefore, it is necessary to study the gas online monitoring system in the switchgear to detect abnormalities in time and eliminate hidden dangers.