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| 大容量新型同步调相机端部磁场分析及放电风险评估
摘 要
随着高压直流输电系统对无功补偿设备快速响应能力和设备容量需求的不断加大，大容量新型同步调相机逐渐取得了广泛应用。同步调相机作为一种无功补偿装置，可以提供动态无功功率，为保障高压直流输电系统电压稳定性起到了关键作用。
同步调相机可以调节直流输电系统的无功功率，能在过励磁、欠励磁甚至失磁的不同工况下运行。随着调相机容量的增大，端部漏磁大大增加，各种非线性因素的影响以及各种机端运行工况，使得端部磁场变得更加复杂。端部磁密的增大会使得端部结构件的损耗和绕组的电磁力升高，长时间运行容易造成端部结构件损坏和绕组振动断裂，造成调相机停机维修。同时端部轴向磁密会在定子铁心定位筋中易产生较大的感应电动势，导致放电风险增大，从而降低同步调相机的使用寿命。
因此，针对调相机的端部磁场和局部放电的问题，基于同步调相机的运行特性，采用时步有限元方法，根据300MVar调相机的实际结构和电磁参数，建立了考虑磁场饱和、畸变等非线性因素影响的调相机端部三维瞬态电磁场仿真模型，并且通过理论验证保证了模型的准确性。并仿真计算了调相机在不同运行工况下的端部磁密、涡流损耗密度和电磁力密度等物理量，研究结果为调相机瞬态场有限元计算和改善端部磁场分布提供了理论依据。
主要研究内容如下：（1）对比分析了调相机在空载、失磁、额定励磁、强励磁不同运行工况的端部电磁场，并研究了金属屏蔽电导率对端部的磁密和损耗密度的影响；（2）揭示了绕组电磁力密度大小和方向在不同工况下的变化规律，同时以电压突升和突降30%为例，研究了调相机暂态过程中的电磁力密度的变化情况；（3）计算了同步调相机在不同运行条件下定位筋中的磁密分布，确定了产生放电的因素，对比分析了感应电动势大小，对调相机定位筋的局部放电风险进行了评估。
关键词：同步调相机；端部磁场；电磁力；局部放电；有限元方法
Abstract
With the rapid response capability of reactive power compensation equipment and the increasing demand of equipment capacity in HVDC transmission system, new large capacity synchronous condenser has been widely used. As a kind of reactive power compensation device,synchronous condenser can provide dynamic reactive power, which plays an important role in improving the voltage stability of power grid in sending- and receiving-end system.
In order to regulate the reactive power of HVDC system,the condenser often operates under the condition of over-excitation, under-excitation or even loss of excitation. With the increase of synchronous condenser capacity, the end magnetic flux leakage increases greatly. The influence of various nonlinear factors and various operating conditions make the end magnetic field more complex. The increase of the end magnetic density will affect the loss of the end structure and the electromagnetic force of the winding. Long time operation is easy to cause the damage of the end structure and the vibration fracture of the winding, resulting in the shutdown and maintenance of the synchronous condenser. At the same time, the end axial flux density will easily produce a large induced electromotive force in the stator core spacer,which will increase the discharge risk and reduce the service life of synchronous condenser.
Therefore, aiming at the problems of the magnetic field and partial discharge at the end of the synchronous condenser,based on the operation characteristics of the synchronous condenser,a three dimensional transient electromagnetic field simulation modelof the synchronous condenser end is established by using the time stepping finite element method, according to the actual structure and electromagnetic parameters of the 300mvar synchronous condenser, and the influence of nonlinear factors such as magnetic saturation and distortion is considered, and the accuracy of the model is ensured through theoretical verification Accuracy. The end magnetic field,loss density and electromagnetic force density of the condenser under different operating conditions are calculated. The research results provide a theoretical basis for the calculation of the end magnetic field and the improvement of the loss distribution in the end region of the synchronous condenser.
The main research contents are as follows: (1) the end electromagnetic fields of the condenser under different operating conditions of no-load, loss of excitation,rated excitation and forced excitation are compared and analyzed,and the influence of metal shield materials on the magnetic density and loss density of each end structure is studied;(2) The end electromagnetic forces under different operating conditions are compared and studied, and the variation of the size and direction of the winding electromagnetic force density is revealed At the same time, the change of electromagnetic force density in the transient process of the condenser is studied by taking the sudden voltage rise and drop of 30% as an example; (3) The magnetic density distribution in the building bar of the synchronous condenser under different operating conditions is calculated, the factors causing the discharge are determined, the induced electromotive force is compared and analyzed, and the partial discharge risk of the positioning bar of the condenser is evaluated.
Keywords: synchronous condenser,fenite elements method,end magnetic field, the electromagnetic force, partial discharge
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