油田35kV配电系统三相电压不平衡问题研究

Study on Three-phase Voltage Unbalance of 35kV Distribution System in Oil Field

油田35kV配电系统中性点一般经消弧线圈接地,运行中存在三相电压不平衡、中性点位移电压偏高的现象。为此,先给出了中性点位移电压的理论计算方法;再以油田某一35kV变电站为例,利用EMTP/ATP电磁暂态程序建立仿真模型,仿真计算了系统的稳态运行特性;提出通过降低中性点不平衡电压的方法将位移电压限制在标准容许值以下;分析出载波通讯用耦合电容器在ABC三相的不均衡安装是该变电站三相电压不平衡的主要原因,耦合电容器调相安装是降低中性点不平衡电压的较好措施;最后现场试验证实措施可行有效。

The neutral point of 35kV distribution system is often earthed by arc-extinction coil in oil field and the manual shift type arc-extinction coil is installed largely. Working method of the manual shift type arc-extinction coil is to select operational tap by rough estimating system coupling current on the basis of net structure. Because the rough estimating method isfft exact, it is possible that three-phase voltage is unbalanced and the neutral point displacement voltage is high. This paper firstly presents calculating formulae of neutral point displacement voltage in theory. Then system simulating model is established using EMTP/ATP and the steady-state working characteristic of system is calculated, taking an example of a 35kV substation. The calculating result indicates that the neutral point displacement voltage could reach 4369V at most, much more than the standard allowable value 3000V, if the operational tap of arc-extinction coil is not chosen suitably. So it is necessary to take methods avoiding such situation. The paper compares two methods and one of them is selected that the neutral point displacement voltage can be limited less than standard allowable value by reducing the unbalanced voltage. By calculation and analysis, it is known that three-phase voltage unbalance is caused by asymmetrical installation of coupling capacitors for communication on A, B, C phase. By fully comparing three methods in allusion to coupling capacitor in their actualized difficulty, effect and the ratio of capability to price, it is sure that adjusting the phase place of coupling capacitors is an effective method to lower the unbalanced voltage. Finally validity and feasibility of the method is validated by test. After the method is actualized, three-phase voltage of the substation is balanced basically. The neutral point unbal- anced voltage can be controlled less than 500V and the neutral point displacement voltage isn＇t more than 1148V, whatever working mode the system is. Such method absolutely satisfies working requirement.