Distinguishing Magnetizing Inrush Based On No-load Closing Power Transformer

As we know, the normal running of power transformer is important to the safety ofwhole power system. In recent years, electricity supply develop rapidly, and theapplication of large-scale power transformer increase continually, the complication oftransformer operational environment and transformer core’s non-linear lead totransformer protection device cannot meet requirement. So it is necessary to in-depthstudy large-sized transformer protection theory and device.The paper introduces the existing transformer models and some principles. Thenthe principle is analyzed. Among which differential protection is used widely. Aproblem affect correctly motion rate of differential protection. It is identification ofmagnetizing inrush current and internal fault. On account of the problem, it studieschange characteristic of instantaneous magnetizing inductance to identifying inrushcurrent and internal fault. When transformer no-load, primary-side inputs transformertripping operation frequently, protection appears error operation. In order to closingsuccessfully by no-load, generally latch-up protection at the moment. Then open upprotection when closing successfully. But if this period appears internal fault, protectionmay refuse operation. The best method is adding protection addition criterion, so thatdistinguishes inrush current or internal fault state. We can use magnetizing inductancevariety to identifying inrush current and internal fault, as protection addition criterion.But it is unknown to secondary-side voltage and current data when no-load closing. Soit only can use primary-side data.The paper comes up with two methods to identifying magnetizing inductance. Theyboth only use primary-side data. One is distinguishing magnetizing inductance based onhysteresis loop. Transformer flux linkage and current have functional relation.According to the transformer primary-side voltage and current data finding hysteresisloop of flux linkage and current. Then solve magnetizing inductance through hysteresisloop of flux linkage and current data point. Finally through ATP and MATLABsimulation software get hysteresis loop and magnetizing inductance. The methodcombines electromagnetic field principle. It is simple and novel. Simulation result isquite good, and corresponded to theory.The other method is firstly practical three phase transformers with Yn/△connectionignores some secondary factor, abstracts mathematical model. Then writing out equation of primary-side by mathematical model. Through algorithm of eliminatingloop current acquires calculation method of magnetizing inductance. Then calculationmethod of magnetizing inductance rewrites matrix form, discrete data of primary-sideby dynamic simulation test substitute matrix. Through least squares method solvesmagnetizing inductance. The method also can get magnetizing inductance preferably.The paper aims at second method goes on the ATP simulation and dynamic simulationtest at the representative running states. And analyses result. Compared with theory, itverifies validity and feasibility.