电力变压器是电力系统中的关键主设备。统计表明，变压器内部故障继电保护正确动作率远远低于发电机和系统的继电保护水平。因此，对电力变压器内部短路故障特征及继电保护方案的深入研究在工程上具有非常重要的意义。本文重点围绕变压器内部短路故障分析的建模、仿真和实验验证而开展研究。首先，通过变压器磁场分析，指出了内部短路故障改变了变压器磁场分布，因此，变压器标称的短路阻抗或无故障情况下测量的参数不能直接用于继电保护设计。在此基础上，基于出现内部短路故障时主要是漏磁场分布决定绕组中电压、电流分布的分析以及主要分布在非铁磁介质中的漏磁场分布可以叠加的原理，提出可以将变压器绕组分段计算漏电感参数，从而建立了基于剖分线圈单元的等值电路，可以灵活地应用于变压器内部短路故障的稳态分析和暂态分析。应用所提出的等值电路模型及所编制的软件对一台实际电力变压器进行了内部短路故障仿真分析，然后与现场实验结果进行比较，结果表明该等值电路能够准确地分析变压器线圈各种内部短路故障。其次，对单侧供电的普通多线圈变压器、分别单侧和双侧供电的自耦变压器发生各种类型内部短路故障进行了仿真分析，并且按照三折线比率制动式纵差保护和零差保护特性验算了差动保护的灵敏度，指出了差动保护对于小匝数内部短路故障不能正确动作，并对其机理进行了分析。这是差动保护应用于电力变压器内部故障保护存在的问题，必须采取辅助措施解决。最后，基于工程设计变压器短路电抗的方法，把内部短路故障引起漏磁场的改变转化为无故障时的漏磁场与故障电流引起的横向漏磁场的叠加，提出了一种基于短路电抗的变压器内部短路故障稳态分析模型。该等值电路不仅计算简单，而且仿真和实验验证表明其分析准确度也能达到工程应用的要求。

Power transformer is one of the most important main equipments in power system. However, it is reported that the correct operation rate of power transformer relay protection much lower than system’s and generator’s relay protection. Therefore, it is of great significance to carry out further studies on the characteristics of internal faults in power transformer and the new relay protection schemes. The work for this dissertation is focused on the modeling of analyzing internal short circuit faults in power transformer, simulations and related tests.First of all, by analyzing the magnetic field distribution at the occurrence of internal short circuits in transformer windings, it is shown that the magnetic field distributions have been changed owing to the fault current. Thus, the rated short circuit impedance of the transformer or measured parameters under normal operation condition can not be used for relay protection design.Based on the analyses it is concluded that under the condition of occurrence of internal short circuits, the voltage and current distributions in the windings are determined by the leakage magnetic fields and the leakage magnetic fields can be calculated using superimposition theorem since the leakage field mainly distributes in the non-ferromagnetic space. Therefore, transformer windings can be subdivided into unit coils and the leakage inductance and resistance are calculated on the basis of unit coils. Then the equivalent circuit is established by connecting unit circuits according to winding’s topological structure and fault setting. It has been shown that it is very convenient to use proposed equivalent circuit in the steady state analysis and the transient analysis of internal short circuits in power transformer windings.A simulation analysis of internal short circuits in a product power transformer has been carried out using the equivalent circuit and verified by the field tests. The results show that the equivalent circuit and designed software can be used in the internal short circuit simulation with satisfied accuracy.Then, the various types of internal short circuits in a single-side charged multi-winding transformer, a single-side charged autotransformer and a double-side charged autotransformer were simulated in details. The sensitivities of the longitudinal differential relay protection and the neutral current differential relay protection with dual slope characteristic were verified with the simulation results and it was pointed out that the differential relay protection could not correctly operate with the internal short circuit of small number of turns. Its mechanism was analyzed and it showed that the extra measures were necessary when applying differential relay to the protection of internal short circuit in power transformer windings.Finally, based on the method of calculating short circuit reactance in power transformer design and on the judgment that the leakage magnetic field caused by internal short circuit can be treated as the superimposition of normal magnetic field and transverse (radial) magnetic field caused by fault current, a new equivalent circuit on basis of short circuit reactance is established. The comparisons between two equivalent circuits show that except for its advantage in simplified calculation, the simulation accuracy of the steady state analysis of internal short circuit is satisfied for practical application.