Winding Capacitance Dividing Method for Powerformer  

作　　者：TIAN Qing LIN Xiang-ning LI Jian-jian TAO Yong-hong 

机构地区：[1]Southeast Shanxi Ultra High Voltage Administrative Bureau, State Grid Operation Company Limited, Changzhi 047100, China [2]Department of Electrical Engineering, China Three Gorges University, Yichang 443002, China [3]State Grid Operation of Company Limited, Beijing 100005, China [4]Department of Electrical Information, Xihua University, Chengdu 610039, China

出　　处：《高电压技术》2008年第5期966-972,共7页High Voltage Engineering

基　　金：Project Supported by National Natural Science Foundation of China(50407010)

摘　　要：It presents a method which can equivalently arrange the capacitance distribution along with the winding of the generator on the terminal and neutral respectively in a reasonable partition,particularly for a type of high-voltage graded insulated cable wound generator,Powerformer.The winding of the Powerformer adopts graded insulation,which leads to the various cable thicknesses in different portion of the winding,and thus,the uneven capacitance distribution.The large capacitive currents and large transient outrush currents resulting from the cable consisting of the stator winding of Powerformer may cause problems to the generator differential protection.Most of literatures available in the field of compensated differential protection focus on the charging current compensation for long transmission line,instead of for generator.The authors give a method which can be used to compensate the capacitive current wholly to improve the reliability of the differential protection of Powerformer.It is proved that the distributed capacitance can be equivalent as the lump circuit with a capacitance partition coefficient ρ,and ρ is proved as a constant no matter whether the generator experiences the normal operation,external phase(s) fault or internal phase(s) fault.The formula of the partition coefficient is provided and the corresponding equivalent circuit of the Powerformer cable to calculate capacitance currents is given.An analysis programming resolving the minimum value of the coefficient ρ is written in MATLAB 7.0/m according to this formula,using the function fmincon() which can work in any type of constraint condition.The program always gets the same global minimum points under the different initial values condition which proves our point by mathematical test.With this new approach to winding capacitance dividing method,the protection scheme used for Powerformer can be validated and improved accordingly.It presents a method which can equivalently arrange the capacitance distribution along with the winding of the generator on the terminal and neutral respectively in a reasonable partition, particularly for a type of high voltage graded insulated cable wound generator, Powerformer. The winding of the Powerformer adopts graded insulation, which leads to the various cable thicknesses in different portion of the winding, and thus, the uneven capacitance distribution. The large capacitive currents and large transient outrush currents resulting from the cable consisting of the stator winding of Powerformer may cause problems to the generator differential protection. Most of literatures available in the field of compensated differential protection focus on the charging current compensation for long transmission line, instead of for generator. The authors give a method which can be used to compensate the capacitive current wholly to improve the reliability of the differential protection of Powerformer. It is proved that the distributed capacitance can be equivalent as the lump circuit with a capacitance partition coefficient ρ, and ρ is proved as a constant no matter whether the generator experiences the normal operation, external phase（s） fault or internal phase （s） fault. The formula of the partition coefficient is provided and the corresponding equivalent circuit of the Powerformer cable to calculate capacitance currents is given. An analysis programming resolving the minimum value of the coefficient ρ is written in MATLAB 7.0/m according to this formula, using the function fmincon（） which can work in any type of constraint condition. The program always gets the same global minimum points under the different initial values condition which proves our point by mathematical test. With this new approach to winding capacitance dividing method, the protection scheme used for Powerformer can be validated and improved accordingly.

关 键 词：电力系统 电容 分配模式 动力设备 

分 类 号：TM712[电气工程—电力系统及自动化] O441.1[理学—电磁学]