海上风电35kV集电系统中性点不同接地方式下过电压分析

Over-Voltage Analysis Under Different Grounding Methods of Neutral Point of 35 kV Collector System of Offshore Wind Power

随着海上风电场规模的增加,35 kV集电系统的海缆截面和长度也不断增加,由于海上风电35 kV集电系统与陆上35 kV配电网中性点接地方式不同,但其海缆绝缘厚度与陆缆标准一致,导致其绝缘水平有较大裕度,造成一定资源的浪费。以某海上风场35 kV集电系统为例,搭建了3条集电线路仿真模型,计算了35 kV海缆在合闸/切除集电线路、合闸/切除箱式变压器等操作工况下和弧光接地下的过电压水平,比较海上风电集电系统中性点在不同接地方式下,不同工况下35 kV海缆在所承受的过电压水平的差异,结果标明:合闸/切除空载和正常运行集电线路及箱变,中性点接地方式对过电压幅值影响不大;切除短路故障集电线路及箱变、集电线路末端弧光接地时,集电系统中性点在经小电阻接地后,过电压幅值得到明显抑制,过电压幅值降低比最高达到43.1%。对比不同接地方式下海缆的过电压水平后,对海上风电集电系统35 kV海缆放宽绝缘设计提供一定的参考价值。

With the increase of the scale of offshore wind farms,the cross section and length of the 35 kV collector system of submarine cables are also increasing.Since the 35 kV collector system of offshore wind power is different from the neutral grounding method of onshore 35 kV distribution network,but the insulation thickness of its submarine cable is the same as the standard of onshore cable,which leads to a large margin of its insulation level and causes a certain waste of resources.The author takes an offshore wind farm 35 kV collector system as an example,builds three collector line simulation models,calculates the overvoltage level of 35 kV submarine cable under the operating conditions of closing/removing collector line,closing/removing box transformer,and arc-light grounding.the difference of overvoltage level of 35 kV submarine cable under different operating conditions in the neutral point of offshore wind power collector system under different grounding methods is compared.The results show that:closing/removing no-load and normal operation collector lines and boxes,neutral grounding method has little influence on overvoltage amplitude;removing short-circuit fault collector lines and boxes,collector line end arc grounding,collector system neutral point in the small resistance grounding,overvoltage amplitude is significantly suppressed,overvoltage amplitude reduction ratio of up to 43.1%.After comparing the overvoltage levels of submarine cables under different grounding methods,it provides some reference value for the relaxed insulation design of 35 kV submarine cables in offshore wind power collector systems.