Transient Process Research Of Controllable Reactor Of Transformer Type

With the rapid development of electric power industry in China, ultra high voltage long distance transmission lines become the solution to the construction of electric systems. But this leads to a critical problem-- Ferranti effect. Controllable Reactor of Transformer Type(CRT) is a new type of controllable reactor. It has the characteristics as fast and smooth adjustment and small harmonic current. CRT is not only able to provide real-time solution to the problem of Ferranti effect but also independent from an over reliance on power electronic technology, which suits China’s actual conditions better. Although CRT is widely concerned and researched in the world, China is still underdeveloped on it. This thesis, taking CRT as major subject, deeply researches its equivalent circuit model, mathematical model, nonlinear core module, electromagnetic transient equivalent network, transient parameter calculation,factors causing transient response and the entire transient process.Based on the structure of CRT, the equivalent circuit model which suits engineering practice is built. In this model, magnetic leakage flux and core saturation characteristics are considered and coupling relations between electric circuit and magnetic circuit is reflected.And the mathematical model of CRT is built which is based on the conception of primary winding. This model and the transient process are researched respectively in the condition of ignoring the core saturation and considering the core saturation. In the condition that the core saturation is ignored, the mathematical model is attained which is based on basic primary winding and the winding inductance coefficient is calculated, the incidence matrix is presented. In the condition that the core saturation is considered, numerical integral is applied to solve the mathematical model of CRT so as to build a pure resistance equivalent electromagnetic transient circuit which contains only current source.Considering that the reliability of CRT could be affected by core saturation during working, function fitting method which has high precision and convenient calculation is adopted to build the mathematical model of core module. By analyzing the fitting results of some common functions, this thesis, describes the nonlinearity of core in the method of piecewise fitting and does tests with MATLAB. The simulation results prove that the fitting method which is adopted in this thesis is able to describe the characteristic of nonlinearity of core module.Transient adjoint parameter equation is built according to the equivalent electromagnetic transient circuit of CRT. And a CRT parameter matrix with the contraction of internal node is obtained. The comparison between the simulation results of ATP-EMTP, the electromagnetic transient simulation software, and the calculation results of the parameter matrix proves that the model is correct and effective.The thesis proposes to divide CRT’s working process into three independent but interactional processes: access, grade change and exit. And the transient processes of the three processes are analyzed and researched respectively. The factors causing transient response in the access process are the initial phase angle of supply voltage at the moment of access and the nonlinearity characteristic of the core. No matter which initial phase angle we adopt, the transient process must inevitably exist. But, when the initial phase angle is ?2/π or 2/π,the instantaneous value of exciting current reaches maximum. The factor causing transient response in the grade change process is the conduction angle of thyristors. The former control windings accessed could be affected by the latter control windings accessed, which makes the decrease of branch current amplitude with the accesses of each latter control winding but intensive instantaneous current with each input. And, whatever the conduction angle of thyristors is, the transition process always exists. The exit process of CRT is controlled by anti-parallel thyristors in series at control windings. Therefore, if the control signal is removed, the component will not be turned off unless zero-cross current appears. And there is a period of transient process after the zero-cross point before the complete exit.