【目的】针对三相绝缘管型母线在运行过程中易发生的接地屏蔽层悬浮故障或劣化故障,进而威胁设备绝缘以及人身安全的问题,本文旨在深度揭示该故障下的电位演化机理,并为故障下电场特性分析提供理论支撑。【方法】首先建立35 kV三相绝缘管型母线的场路耦合有限元模型,分析了屏蔽层悬浮状态下的电场畸变特征以及电位分布。同时,构建了考虑分布参数的三相耦合等效电路模型,计算了屏蔽层悬浮电位随对地杂散电容及接地电阻的变化规律,并进一步结合工程实际中1 km线路模型分析分布参数对感应电压的影响。【结果】结果表明,与正常工况下相比,屏蔽层悬浮状态下故障相的表面电位随导体升高,相间空气域出现电场畸变现象;主绝缘电容显著大于对地杂散电容,屏蔽层丧失电位钳位作用。屏蔽层在电阻接地工况下,分布参数带来的位移电流累积导致长距离母线对接地电阻变化更为敏感。【结论】接地屏蔽层悬浮将导致持续稳定的高电压状态,其电场畸变会严重破坏绝缘管型母线的全屏蔽特性。为确保人身安全以及设备绝缘安全,基于本文推导出的估算接地电阻安全阈值的参数化解析模型,建议将35 kV电压等级下1 km长线路绝缘管型母线接地电阻值控制在12.3 Ω以内,以留有充足的安全裕度。

[Objective] Aiming at the problems that the grounding shield layer of three-phase insulated tube-type busbars is prone to floating or degradation faults during operation, which further threatens equipment insulation and personal safety, this paper intends to deeply reveal the potential evolution mechanism under such faults and provide theoretical support for the analysis of electric field characteristics under fault conditions. [Methods] First, a field-circuit coupled finite element model of 35 kV three-phase insulated tube-type busbar was established,and the electric field distortion characteristics and potential distribution under the shield floating state were analyzed. Meanwhile, a three-phase coupled equivalent circuit model considering distributed parameters was constructed to calculate the variation law of the floating potential of the shielding layer with respect to the stray capacitance to ground and the grounding resistance. Furthermore, combined with a 1 km line model in practical engineering, the influence of distributed parameters on the induced voltage was analyzed. [Results] The results show that, compared with normal operating conditions, the surface potential of the faulty phase rises with the conductor under the floating shield layer, and electric field distortion occurred in the interphase air domain. The main insulation capacitance was significantly larger than the stray capacitance to ground, causing the shield layer to lose its potential clamping function. Under the resistance grounding condition where the shield layer is grounded through a resistor, the accumulation of displacement current caused by distributed parameters made long-distance busbar more sensitive to changes in grounding resistance. [Conclusion] Floating of the grounding shield layer results in a sustained and stable high-voltage state, and the associated electric field distortion severely damages the full shielding characteristic of insulated tube-type busbars. To ensure personal safety and equipment insulation safety, based on the parametric analytical model derived in this paper for estimating the safety threshold of grounding resistance, it is recommended that the grounding resistance of 1 km long insulated tube-type busbars at the 35 kV voltage level be controlled within 12.3 Ω to maintain sufficient safety margin.

安徽省高校协同创新项目(PA2024AGXC0123)