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| Influence of Interface Spraying Mg(OH)2 on DC Electrical Properties of DC Cable Factory Joints Insulation Transition Layer |
| Meng Fanbo1,2, Chen Xiangrong1,2,3,4, Hong Zelin1,2, Shi Yiwen1,2, Huang Ruobin5 |
1. College of Electrical Engineering Zhejiang University Hangzhou 310027 China
2. ZJU-Hangzhou Global Scientific and Technological Innovation Center Hangzhou 311200 China
3. Zhejiang Provincial Key Laboratory of Power Semiconductor Materials and Devices Hangzhou Global Scientific and Technological Innovation Center Zhejiang University Hangzhou 311200 China
4. Advanced Electrical International Research Center International Campus Zhejiang University Haining 314400 China
5. Ningbo Orient Wires & Cables Co. Ltd Ningbo 315000 China |
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Abstract Factory joint is a key accessory to realize long-distance power transmission of HVDC submarine cable. To improve the insulation properties of the HVDC cable factory joint interface, this paper prepared Mg(OH)2 by hydrolysis method, and configured 4 kinds of Mg(OH)2 reagents with different concentrations (weight fractions are 0.000 1%, 0.000 5%, 0.001% and 0.01%, respectively), which were sprayed at the interface of the factory joint.
A trace amount of Mg(OH)2 particles were introduced at the interface. The particle morphology and the physical and chemical properties of the samples before and after the introduction of Mg(OH)2 were analyzed by thermogravimetric analysis, scanning electron microscopy and transmission electron microscopy. The electrical properties at 30℃, 50℃ and 70℃ before and after the introduction of Mg(OH)2 into the factory joint were analyzed using the electrical conductivity, space charge and breakdown field strength. The results show that Mg(OH)2 can be combined with alcohol well, it still has good dispersibility after standing for 1 h, and the spraying method can achieve good dispersion of Mg(OH)2 at the interface. The Mg(OH)2 prepared by the hydrolysis of MgO is flaky and the particles are looser. Compared with MgO, the agglomeration of Mg(OH)2 is improved. With the increase of the sprayed Mg(OH)2 concentration at the interface, the conductance of the sample first decreased and then increased, and the sample sprayed with 0.001% showed the smallest DC conductivity. Unmodified samples are prone to negative charge accumulation at the interface, especially at low temperatures. High temperatures help reduce charge build-up at the interface. For the samples sprayed with a small amount of Mg(OH)2, a significant charge suppression effect appeared at both low and high temperatures. However, spraying Mg(OH)2 over it will increase the space charge accumulation at the sample interface. Among them, interfacial spraying of 0.000 5% Mg(OH)2 can significantly suppress negative charge accumulation. With the increase of the sprayed Mg(OH)2 concentration, the interface samples showed an increasing trend at different temperatures, and the DC breakdown field strength of the factory joint samples can be significantly improved after spraying with Mg(OH)2. Based on the space charge depolarization current, the trap characteristics of different samples were calculated, and it was found that after the introduction of Mg(OH)2 at the interface, shallow trap characteristics were exhibited at different temperatures. In addition, an interface molecular chain model was constructed, and the effects of electron cloud orbits and density of states on the insulating properties of the samples before and after the introduction of Mg(OH)2 were analyzed by quantum chemical calculations. The results show that for pure XLPE samples, the gain and loss of electrons easily occur near the cross-linking point, while the gain and loss of electrons easily occur around Mg(OH)2 after the introduction of Mg(OH)2. The results of the density of states distribution of different molecular chain models show that after the introduction of Mg(OH)2, the overall density of states curve shifts to the left, and a new density of states peak appears locally. This indicates that a new trap level is locally introduced. The introduction of new traps increases the trapping and detrapping of charges in the process of migration, and charge jumping consumes a certain amount of energy, making it difficult to accumulate charge kinetic energy.
In summary, the above results show that the appropriate amount of Mg(OH)2 can effectively improve the insulation properties of HVDC cable factory joints.
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Received: 25 July 2022
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2023, Vol. 38 
