Research On Switching Transient Electromagnetic Interference In Substations

Supported by National Natural Science Foundation of China under grant No. 50077006, the measurement technology and analysis method of transient electromagnetic interference due to switching operations in substations are researched in this paper. The main contributions are as follows:1. An optical fiber sensing system of transient magnetic field is developed. In order to compensate the frequency characteristic of the probe, a digital frequency balancing method is proposed, and the digital balancing network is designed. The frequency range of the sensing system is 40Hz~100MHz, the measurement range is 1A/m~1100A/m. The linearity of the sensing system is better than 0.97%, the measurement uncertainty is less than 5%, the length of the optical fiber is 50m. Using this sensing system, the transient magnetic fields as operating the 35kV reactor are firstly measured in China.2. An optical fiber sensing system of transient electric field is developed. The frequency range of the sensing system is 40Hz~100MHz, the measurement range is 10V/m~100kV/m. The measurement uncertainty is approximately 5%, and the length of the optical fiber is 50m.3. Many transient interference waveforms are measured and recorded during switching operations in three 500kV-substations. These waveforms are analyzed, and the characteristic parameters are summarized in this paper based on statistics analysis. The results indicate that the worst case is disconnect switching operations.4. The agreement between the waveforms of the immunity test standards and the measured interference waveforms are assessed. Based on the assessment results, it is suggested that for the transient voltage immunity test, the 6MHz frequency should be included in the test waveform. The software is developed for analyzing the immunity test waveforms, the measured waveforms and the predicted waveforms.5. Based on the concept of electromagnetic topology, a systematic analysis method of the coupling mechanism of the interferences is proposed in this paper. An automatic measurement system of transfer function of the interference network is developed, and the anti-interference characteristic of a relay protective equipment is analyzed using this system. The results show that the interference components up 1MHz are not mitigated in the equipment, the design should be improved.The hardware and software developed in this paper are useful for characterizing the transient electromagnetic environment of high voltage substations.