Transactions of China Electrotechnical Society  2023, Vol. 38 Issue (14): 3930-3942    DOI: 10.19595/j.cnki.1000-6753.tces.220872
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Factors Analysis and Robust Design of Electromagnetic Leakage Protection Characteristics
Li Kui1,2, Xu Zijian1,2, Lu Zhiwei1,2, Wu Yi1, Hu Bokai1,2
1. State Key Laboratory of Reliability and Intelligence of Electrical Equipment Hebei University of Technology Tianjin 300130 China;
2. Key Laboratory of Electromagnetic Field and Electrical Apparatus Reliability of Hebei Province Hebei University of Technology Tianjin 300130 China

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Abstract  Electromagnetic leakage protection is an important leakage fault protection technology greatly influenced by component parameters and requires high requirements for the batch production process, resulting in high production costs. The problem of instability of electromagnetic leakage protection characteristics is studied to improve its robustness and to solve the constraints of batch production of electromagnetic leakage protectors.
Electromagnetic leakage protection characteristics, such as leakage operating current and operating time, depend on the parameters of the residual current transformer and its matching resistance and capacitance. If the leakage operating current is a specific value, the matching relationship curve of R1 and C1 is like the letter “U”. As C1 increases, the operating time tC increases and then decreases. The maximum value of operating time tC appears around the resonant capacitor, increasing with the increase of resonant capacitance. The inductance varies for different residual current transformer core magnetic parameters, resulting in different resistance and capacitance to be matched. However, the shape of the curve for the matching relationship between resistance and capacitance is the same, simply shifting on the axis, as shown in Fig.A1a, with a similar variation in the operating time tC, as shown in Fig.A1b.
Although different compensation capacitors C1 are available to meet the requirements of the leakage protection characteristics, the stability of the characteristics varies. The leakage protection characteristics are robust if C1 is smaller than the resonant capacitance, and the tolerance of C1 has less effect on it. At the same time, the leakage protection characteristics are also influenced by the magnetic parameters of the residual current transformer core, such as Bs, Br, and Hc. The stability of the leakage protection characteristics varies under different Bs, Br, and Hc, with Br and Hc having a large impact and Bs having a small impact. For the same value of compensation capacitance, there is a lower limit kmin for Br/Hc. If Br/Hc<kmin, the leakage operating current and operating time will change rapidly with Br/Hc. While Br/Hc>1.5kmin, the value of Br/Hc is guaranteed to be greater than kmin when the dispersion of Br and Hc reaches ±20 %. In this case, the leakage protection characteristics are less affected by the dispersion of magnetic parameters, and its robustness is good.
According to the above analysis, the matching design of the residual current transformer and leakage detection circuit parameters are carried out, as shown in Tab. A1. Under the core magnetic parameters of the original scheme, the matching of R1 and C1 is carried out, and the leakage protection characteristics can meet the requirements. However, if the component parameters offset up to 10 % due to the dispersion of component parameters or the temperature of the environment, the value of leakage operating current IΔ exceeds the rated leakage operating current value IΔn, and the leakage protector can not be operated with IΔ=IΔn. With a 10% change in capacitance and the magnetic parameters shifted in the direction of the maximum shift in the protection characteristics, the offset of the leakage operating current value is less than 6 %, and the offset of operating time tC is less than 7.1 % with the optimized scheme 1 and 2. The robustness of the electromagnetic leakage protection characteristics is improved, which can be obtained from the fact that the protection characteristics vary less than the parameters of the components. The consistency and stability of the leakage protection characteristics can be ensured during manufacturing and operation with the optimized scheme, which is conducive to batch production.
Key wordsElectromagnetic leakage protection      residual current transformer      leakage protection characte- ristics      robustness      parameter matching design     
Received: 19 May 2022     
PACS: TM561  
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Li Kui
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Cite this article:   
Li Kui,Xu Zijian,Lu Zhiwei等. Factors Analysis and Robust Design of Electromagnetic Leakage Protection Characteristics[J]. Transactions of China Electrotechnical Society, 2023, 38(14): 3930-3942.
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