The Study On Suppression Of Fundament Ferroresonance In Neutral-Grounded System

Ferroresonance is an internal overvoltage in power system. It is a huge threat to the safetyand operational stability of power system. Many useful measures to inhibit ferroresonance hadbeen obtained after the long time research. But because of the complex of grid connection, thecharacters in different grids wouldn’t be the same. And the measure to eliminateferroresonance cannot be used general. And the ferroresonance in neutral-grounded systemusually happened at the high voltage side. It’s more harmful. According to the runningexperience, the fundamental ferroresonance in neutral-grounded system had happened most.So, this thesis only discussed the fundamental resonance to prevent and inhibit fundamentalresonance.This thesis analyzed the basic theories of ferroresonance, and then induced the constraintequation of the circuit. Then introduced the characteristic of jump phenomena, confirmed thenecessary conditions of ferroresonance. This thesis adopts power-frequency excitationcharacteristic of non-linear inductance to analyze fundamental resonance, and deduced theexpression of power-frequency excitation characteristic. Take a non-linear inductanceparalleling a linear resistance as the model of PT in EMTP. And then the U-I characteristic hadbeen converted into i-φ characteristic with the program SATURATION in EMTP.In the area of theory study, according to power-frequency excitation characteristic, thisthesis induced the criterion for fundamental ferroresonance, obtained equation of the criticaldamping resistance. Then it took the wiring diagram of the ferroresonance substation forexample to analyses the two conditions that open the breaker and open the isolation breaker tojudge whether the ferroresonance would happen, and then to analyses another two conditionsthat paralleling a small resistance on the Y windings of transform secondary side and cut downthe resistance in theoretically. Next it built the simulation model of110kV system by usingEMTP for checking above analysis one by one.Through the Theory analyses and simulation checked, although it can inhibit ferroresonance effectively by using the method that paralleling small resistance. But when cutit down, ferroresonance would happen again. So, this thesis had improved the method by add aelectrolytic capacitors after a full bridge rectifier circuit. It can absorb the power of resonance,and also can prevent the capacitor voltage to influence the system. Then two situations thatopen the break and cut off the resistance had been simulated by using EMTP.