Research Of Simulation Testing System For Power Transformer Protection

This paper presents a transient simulation testing system for power transformer protection and its software package whose hardware platform is transient testing system of portable protection relay. Transient testing of the power transformer protection comes true with this system. And this system is proved to be applicable in practice. In this paper, Electromagnetism transient numerical calculation theory has been used to research three-phase two windings transformers and three-phase three-legs transformers, which are used widely in power system. Inductance matrix has been made with geometry parameter of transformer and its testing value. Then non-linear transient model of transformer was made.Electrical connections of the windings, alternate coupling and nonlinearity of the iron core have been considered in this model. As the core of the testing system, this model can simulate all operating conditions such as transformer's normal running, shutting breakers with load or without load, fault within the zone or outside and turn-to-earth fault, and then produce its waveform data.Because of ferromagnetic elements, magnetic induction B and magnetic field H is non-linear, which is the main cause that high inrush current occur during the transformer energisation. So precise description of ferromagnetic elements' magnetization characteristic is the base of setting up accurate inrush current model of transformer.In this dissertation fitting method is used in forming the basic magnetization curve of the iron core. Based on comparing some fitting function such as polynomial, hyperbola and exponential function, fitting method by stage is proposed in this paper. In the method, different fitting function is used at different stages and described the elementary magnetization curve accurately.The parameters which the transformer model need can not be gotdirectly from the transformer's nameplate and the characteristic experimentation result, such as circle number of transformer's windings, area of the core's section and the length of magnetic path. All parameters are computed according to the parameters on the nameplate, the characteristic experimentation result and some experiential formula.In this paper, the transformer protection transient simulation testing software package has been researched. At first, it forms corresponding simulation model according to transformer's parameters and test's conditions inputted by users. Then it solves the mathematics model and produces simulation waveform data and saves these data as COMTRADE files according with IEEE standard. Most protection transient simulation test systems support this file form. Then using the playback function of the testing system, it reads in the COMTRADE files and plays back simulation waveform and then begins to test the transformer protection.The transformer model researched in this paper considers unifying between complexity and precision and builds strong foundation for embedding model in DSP of transient testing system and realizing real-time and closed loop testing to transformer protection.The simulation waveform data computed by this testing system are accordant with result of EMTP. The transformer protection transient simulation testing system is composed of the transient testing software package and protection relay transient testing system and realizes entire testing of transformer protection.