| Ferroresonance is an overvoltage phenomenon existing in the power system,which seriously threatens the safe and stable operation of the entire power grid system.In order to eliminate the ferromagnetic resonance,nowadays,the neutral point of the high-voltage side of the electromagnetic voltage transformer is mainly equipped with a resonance eliminator(non-linear resistance)and a high-resistance resistance;resonance elimination measures such as 4PT are adopted,but these resonance elimination methods will lead to The voltage at the end of the PT rises,the zero-sequence voltage of the open triangle is too low,and the circulating current is generated.In order to effectively suppress the ferromagnetic resonance caused by the busbar PT of the distribution network,this paper proposes a method of eliminating resonance in the distribution network by adding a gap and a series combination of resistors at the neutral point of the primary side of the electromagnetic voltage transformer.In this paper,Based on the analysis of the mechanism of ferromagnetic resonance in the distribution network and comparing the advantages and disadvantages of the existing resonance elimination measures,this paper proposes a resonance elimination method in which a series combination of gaps and damping resistors are installed at the neutral point of the bus PT high voltage side.By reasonably setting the gap discharge voltage,the neutral point insulation can be effectively protected,and when the ground fault occurs and disappears,the neutral point’s potential offset can be used to suppress the development of resonance and break the resonance state through the gap.The resistance method prevents the problem of excessive neutral point current due to gap breakdown.Through the principle and function of the device,the selection method of gap and resistance is given.Taking the 10kV busbar PT as the application object,the 10kV distribution network distributed parameter circuit model is built using electromagnetic transient analysis software.According to the selection principle of gap and resistance,the discharge voltage of the gap is 2500V and the best resistance is obtained through simulation calculation.The value is 2000Ω.Using the simulation model,the proposed method of eliminating the resonance of the gap and the resistor in series is compared with the traditional PT high-voltage side with high-resistance resistance,non-linear resistance,and PT neutral point grounded by single-phase PT(4PT)..The results show that the method of installing a gap and a damping resistor on the primary side of the PT has the characteristics of shorter elimination time and lower voltage level at the PT end compared with the method of connecting a large damping resistor to the neutral point of the PT primary side;Compared with the method of connecting the neutral point of the PT primary side with the non-linear resistance,the method of installing the gap and the damping resistor combination has the characteristics of shorter elimination time;the method of installing the gap and the damping resistor on the PT primary side is compared with the method of 4PT It has the characteristics of short harmonic elimination time,does not affect the PT open triangle zero sequence voltage measurement,and the ground point capacitive current is small,and has a better comprehensive resonance elimination effect.The neutral point of the primary side of the electromagnetic voltage transformer is installed with a gap and a resistance series combination of the distribution network harmonic elimination method,which can maintain the safe and stable operation of the distribution network,suppress the overvoltage and overcurrent generated by the ferromagnetic resonance,and protect the voltage transformer.Improving the reliability of the system is of great significance. |
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