The accuracy of collected data is the foundation of the vitality of online monitoring of power equipment. Without accurate and reliable original data, all algorithms, structures, and concepts are just castles in the air.
Zinc oxide arresters are important equipment for preventing overvoltage in power systems, and are currently widely deployed in online monitoring areas. The zinc oxide arrester online monitoring device generally installs a current transformer through the ground conductor of the zinc oxide arrester to obtain the full leakage current of the zinc oxide arrester under the operating voltage, and then calculates the resistive current. The online monitoring device realizes the monitoring and judgment of zinc oxide arrester aging, moisture and other issues by calculating and monitoring the full current and resistive current of the leakage current.
The zinc oxide arrester online monitoring device is very clear in principle and has been installed in large numbers, but it has no obvious effect in actual operation. The reason is that there is a problem with the accuracy of the original data. According to literature statistics, among the online monitoring devices of zinc oxide arresters installed in a certain area, the proportion of abnormal operation is as high as 56.3%, of which 70% have abnormal data. With so much abnormal data, the operating effect of the online monitoring device can be imagined.
There are many factors that affect the accuracy of leakage current data measurement under the operating voltage of zinc oxide arresters, such as temperature, interphase stray capacitance, etc., but these factors can generally be compensated and corrected through algorithms through later data processing. However, there are deficiencies in the structure, installation method and cooperation of the current zinc oxide arrester with the online monitoring device, making it impossible to guarantee the accuracy of the measurement data. The structure and installation method of zinc oxide arrester are shown in Figure 1. The current transformer of the online monitoring device is installed at the location of the grounding down conductor. This installation method causes the measurement data to be affected by the insulation of the base and the contamination of the outer surface of the arrester. If the chassis insulation is reduced, the measured full leakage current will be smaller than the actual value. The dirty current of the external insulation will make the measured full leakage current larger than the actual value. This effect will be very large especially when the external insulation is seriously polluted and superimposed with high humidity.
In order to solve this problem. We propose a zinc oxide arrester with built-in current transformer. Its structure and installation method are shown in Figure 2. This kind of zinc oxide arrester has a structural change. A current transformer is arranged outside the valve core of the arrester and inside the outer insulation. The current transformer is arranged at the bottom of the arrester, and the metal shell is connected to the lower flange to ensure operation at ground potential. The zinc oxide arrester valve core passes through the current transformer, so that the current transformer can accurately measure the full current of the leakage current under the operating voltage of the zinc oxide arrester. The zinc oxide arrester online monitoring device directly collects the signal output by the current transformer. This structure and installation method ensure that the measurement results are not affected by contamination of the base insulation and external insulation. At the same time, the installation form is simplified (no insulating base is required), which improves the safety and reliability of operation.
At present, online monitoring of power equipment has reached a starting stage of rapid development, and various newer concepts and technologies are emerging one after another. We should pay more attention to the issue of data collection, so that accurate data can support the stable operation of the entire system and the healthy development of the entire industry.
