基于配电网低压台区三相不平衡治理策略研究和应用

Research and Application of Three-phase Unbalance Control Strategy Based on Low-voltage Station Area of Distribution Network

在我国,城乡低压配电网中普遍采用三相四线制的供电方式,主要由于该供电方式既可以满足三相动力负荷的用电需要,也能够为众多的单相照明及其他单相负荷提供电源。在理想的三相四线制低压配电系统中,三相电流和电压有着同样的幅值,且A、B、C相位互相差120°,这样的系统就叫做三相平衡系统(或称为三相对称系统);当三相负荷完全平衡时,零线电流为零,零线上就没有损耗,这当然是配电最理想的状态。然而由于大量照明以及其他单相负荷的存在,低压电网规划和分配到各相电源的负荷很难做到均衡,即使按照设计容量进行了平衡分配,由于负荷运行是动态变化而无法预控的,这就造成了10 kV配变普遍存在着三相负荷不平衡的现象。三相负荷不平衡既包括三相电压不平衡,也含三相电流不平衡,两者是相辅相成的,其均与线路阻抗的对称性、用户负荷特性及负荷配置有关。由于实际工作中普遍存在着严重的三相电流不平衡的超标问题,而治理了三相电流不平衡超标也就保障了三相电压不平衡的合格,因此本文重点研究三相电流不平衡的影响,并提出不平衡超标的治理措施。

The three-phase four-wire power supply method is commonly used in China’s urban and rural low-voltage distribution networks.The main reason is that the power supply method can not only meet the power needs of three-phase power loads,but also provide a large number of single-phase lighting and other Phase loads provide power.In an ideal three-phase four-wire low-voltage power distribution system,the three-phase current and voltage have the same amplitude,and the phases of A,B,and C differ by 1200 from each other.Such a system is called a three-phase balanced system(or three-phase balanced system).When the three-phase load is fully balanced,the neutral current is zero,and there is no loss on the neutral line,which is of course the most ideal state for power distribution.However,due to the existence of a large number of lighting and other single-phase loads,it is difficult to balance the load of the lowvoltage grid planning and the distribution of the power to each phase.Even if the balance is allocated according to the design capacity,the load operation is dynamically changing and cannot be controlled.As a result,the phenomenon of unbalanced three-phase loads is common in 10 kV distribution transformers.Three-phase load imbalance includes both three-phase voltage imbalance and three-phase current imbalance.The two are complementary and they are related to the symmetry of line impedance,user load characteristics and load configuration.Because serious three-phase current imbalance exceeds the standard in actual work,the treatment of the three-phase current imbalance exceeding the standard also guarantees the compliance of the three-phase voltage imbalance.Therefore,this article focuses on the impact of the three-phase current imbalance,and Propose governance measures after the imbalance exceeds the standard.