Research On The Novel Low Resistance Grounding System

In the distribution network of our country, such as Guangzhou, Shanghai and Beijing etc, neutral grounding through low resistance has been widely used. In the low resistance grounding systems of our country, the grounding resistors are linear resistors, the accidents of grounding resistors burned up occurred occasionally in the past years. When there is an intermittent or non-metallic grounding fault, the current of fault line is relatively small, if the fault current is smaller than the action value of relay protection, the zero sequence over-current protection of the fault line won't work, and the grounding resistor will burn, most accidents happen at this condition, which has been the main factor restricting the application of neutral grounding through low resistance.To solve this problem, this paper proposes “Novel Low Resistance Grounding System” based on novel grounding resistor, the resistor is a transformer with two SCRs in the secondary side. This system sets a threshold voltage to guarantee the safety of power network, when the neutral point voltage is lower than the threshold voltage, this system will operate in the state of large impedance grounding; but when the neutral point voltage is higher,the system will operate in the state of low resistance grounding. This new grounding model has successfully solved the problem of grounding resistor burns up because of long time heating, and it's a more safe and reliable grounding model.This paper has designed a novel resistor, which can not only meet the requirements of Novel Low Resistance Grounding System, but also has the characteristics of high reliability, economic and applicable etc, and Ansoft has been used to do simulation and calculation for this design. At last, theoretical analysis and simulation has been done to prove this new system can solve the existing problems, which current low resistance grounding systems have, and by comparing the novel low resistance grounding system with the ordinary low resistance grounding system, the result proves that the new system is more safe and reliable.