Study And Simulation Calculation Of Overvoltage And Overcurrent Caused By Saturated Electromagnetic Voltage Transformers In Power Distribution Networks

Ferromagnetic resonance and very low frequencies oscillations caused by saturated Electromagnetic Voltage Transformers often occur in the system neutral point isolated. They can endanger the voltage stability and safety of electric equipments. In this paper, a systemic simulation using Electro-magnetic Transient Program (EMTP) is presented. It is a simulation about electromagnetic transient caused by saturated electromagnetic voltage transformers in 10 kV isolated neutral system. The conclusion is that: if the transmission lines or cables are short (the equivalent capacitance to ground is correspondingly small), single-phase ground fault caused by an intermittent arc or there-phase closing will excite power frequency resonance or subharmonic ferroresonance, then it bring ferromagnetic resonance overvoltage and overcurrent passing through electromagnetic voltage transformers; contrariwise the transmission lines or cables are long (the equivalent capacitance to ground is correspondingly large), single-phase ground fault caused by an intermittent arc will lead the transient shock, which fault shall engender very low frequencies oscillations in the circuit composed by electromagnetic voltage transformers and capacitance to ground of there-phase transmission lines or cables, that bring very large overcurrent passing through electromagnetic voltage transformers.This paper presents some correlation curves connected system parameters with overvoltage and overcurrent, and some representative wave forms diagrams about overvoltage and overcurrent.Through simulation calculation, the paper discussed all kinds of eliminations may be restrain those overvoltage and overcurrent, and presents a new elimination can effectively restrain those overvoltage and overcurrent. The new elimination resolve the problem of ferromagnetic resonance overvoltage and very low frequencies oscillation overcurrent caused by saturated electromagnetic voltage transformers. Then some high voltage prototypes simulation tests (10 kV) is presented in this paper. The results of tests are consistent with the result of simulation.