220kV变压器中性点经小电抗接地方式  

Neutral Grounding via Small Reactance for 220 kV Power Transformers

作　　者：于化鹏[1] 陈水明[1] 杨鹏程[1] 印华 崔婷 

机构地区：[1]电力系统及发电设备控制和仿真国家重点实验室(清华大学电机系),北京市海淀区100084 [2]重庆电力科学试验研究院,重庆市渝北区401123

出　　处：《电网技术》2011年第1期146-151,共6页Power System Technology

摘　　要：为了限制短路电流和满足继电保护整定的需要,我国220 kV电力系统采用的是部分变压器中性点接地方式。这种接地方式会使不接地变压器的中性点产生过电压,若失地后发生单相接地故障更可能使中性点过电压上升到相电压,虽然可以用避雷器和间隙对此进行保护,但间隙放电分散性很大,很可能误动,且可能会与避雷器绝缘配合失调。为此建立了一个重庆地区的220 kV电网,使用PSCAD/EMTDC软件计算了中性点加装小电抗后的中性点过电压及短路电流。计算结果表明:中性点串接小电抗后,中性点的过电压会大幅下降,不再会出现失地现象,中性点电压也不会再出现高达相电压的过电压,中性点不必再安装间隙,只安装避雷器限制雷电过电压即可,免去了绝缘配合失调的可能性;并且,中性点加装小电抗后,变压器绕组流过的单相短路电流会下降,可以防止变压器绕组上流过的电流过大,损坏变压器。最后分析了中性点加装小电抗对继电保护的影响。To suppress short-circuit and meet the demand of the setting of protective relaying, only part of neutral points of power transformers of 220 kV power systems in China are grounded, and this grounding mode leads to overvoltage appeared at the neutral points of non-grounded power transformers. In 220 kV power system adopting such a neutral grounding mode, the neutral overvoltage may rise to phase voltage when single-phase earth fault occurs while the grounding is in failure. Although arrestors and gap can be used to suppress neutral overvoltage, however due to the dispersity of gap discharging the malfunction of the gap may occur and the insulation coordination of gaps with arrestors may disorder. For this reason a model of 220 kV power system in Chongqing area is built and neutral overvoltage and short-circuit current are computed by PSCAD/EMTDC software when the neutral of 220 kV power transformer is grounded via an additional small reactance. Calculation results show that under neutral connected in series with small reactance, the neutral overvoltage evidently reduces and the grounding failure no more occurs, and the neutral overvoltage as high as phase voltage no more appears, so it is enough to install arrestors to the neutrals and it is not necessary to configure gaps for neutrals. Besides, after the small reactance is added to neutral the single-phase short-circuit current flowing through transformer winding will be decreased, thus the damage of transformer can be prevented. Finally, the influences of adding small reactance to neutral on protective relaying are analyzed.

关 键 词：中性点 变压器 小电抗 短路电流 工频过电压 

分 类 号：TM86[电气工程—高电压与绝缘技术]