周期性脉冲电热效应下环氧树脂绝缘材料的老化机理与寿命评估

Valve reactor is a key protective element of HVDC convertor valve, which works under the periodical impacts of DC saturable current, switching-on trasient impulse current,transient impulse voltage of valve switching on and off,and corresponding trermal stress. It is now unclear of the aging mechanisims and lifetime of its Resin Epoxy insulation materials, which becomes a fatal risk that threatens the reliability of HVDC system. Therefore, the aging mechanisms and lifetime estimation are going to be studied according to the special working conditions of implulsive electrical and thermal stess on the insulation of valve reactor. By theoretical simulation and experimental test, research the impluse voltage, pulse current and saturable DC current generated by the switching-on and switching-off transient process,study the distribution of repetitive pulsive electrical and thermal stess on Resin-epoxy insulation materials by the transient pulse voltage and pulse curent, then setup the stress model of Resin-epoxy insulation materials. Based on the stress model, deal the test samples with corresponding aging conditions,then apply material structure analyzing techniques as the thermal loss, FT-IR spectrum and SEM to measure the structural properties of the insulation samples, and test the macro mechanical and electrical properties of the tested samples, to research the damaging mechanisms of the materials under the periodical pulsive electrical and thermal stesses. According to the experimental data, fit the aging lifetime model equation of multi-stress, which results will provide reasonable bases for the lifetime estimation of the HVDC valve reactor insulation.

饱和电抗器是HVDC换流阀的核心保护元件，换流阀周期性的导通与关断使饱和电抗器绝缘长期承受脉冲电热应力的联合作用，在此工况下其环氧树脂绝缘的老化特性和运行寿命仍不清楚，成为影响高压直流输电可靠性的重要隐患。为此，本项目拟深入开展环氧树脂在周期性脉冲电热应力联合作用下的老化机理及寿命评估的研究。仿真和试验相结合，研究换流阀周期性开通和关断的冲击电压、电流和直流饱和电流等引起的脉冲电、热应力在电抗器绝缘上的动态分布，建立脉冲电热应力联合作用模型。基于该模型制定老化条件，通过周期性脉冲电热应力联合作用的加速老化试验对环氧绝缘试样进行处理，采用热重、红外光谱、扫描电镜等材料结构分析技术和对材料宏观电气及机械性能的测试，研究环氧材料在周期性电热冲击联合应力下的损伤、破坏机理。根据老化试验数据建立周期性脉冲电热应力联合作用下环氧树脂材料的多因子老化寿命模型，为饱和电抗器绝缘老化寿命的评估提供科学依据。

本项目对饱和电抗器在正常运行情况下的脉冲电压、电流和损耗特性进行了深入的调研和分析，以锦屏-苏南±800kV/4750A特高压直流输电工程中使用的A5000换流阀的试验数据为基础，通过仿真与试验相结合的方式，研究了换流阀饱和电抗器在开通/关断暂态情况下环氧绝缘内部的脉冲电场动态分布规律；从阀用饱和电抗器的结构、电磁特性出发，建立了多铁芯阀用饱和电抗器宽频动态电路模型，并采用试验对该模型进行了验证；基于饱和电抗器铁芯在开通/关断暂态下的电压、电流波形及铁磁损耗实测数据，通过等效导体发热模型仿真研究了微秒级冲击电流作用下的动态发热特性及热应力分布规律，并采用us级极快速响应的红外脉冲测温系统进行了试验验证。基于饱和电抗器运行工况特点，设计了重复频率的微秒级脉冲电压发生器和冲击电流发生器，搭建了环氧树脂绝缘材料在周期性脉冲电、热应力作用下老化研究的试验平台；试验研究了环氧绝缘试样在周期性微秒级脉冲电、热应力及其联合作用下，采用耐压、局放、红外吸收光谱、扫描电镜等手段研究了材料的老化特征，研究发现，饱和电抗器在正常运行条件下周期性的开通/关断等暂态过程，在绝缘上产生的脉冲电热应力均低于材料的耐受值，对环氧树脂的老化效应可忽略不计。通过施加超出正常工况的加速老化条件，采用耐压、局放手段研究得出了材料的老化寿命数据，基于Weibull分布的参数模型和多因子联合老化寿命模型，建立了环氧绝缘在脉冲电热应力独立和联合作用下的寿命评估方程和评估方法。