| With the development of the country economy, a great change of power distribution network is occurring, especially in the city. On the one hand, distribution circuit is changing from overhead power line to cable line, it lead to reduce electromagnetism pollution, avoid the contravention between pole and tree, add the greenbelt of the city, and beautify the environment. However, capacitance effect resulted from the cable will make the steady-state over-voltage on the power distribution network. On the other hand, because of the fluctuating load, such as arc furnace and railway traction locomotive, the voltage of the network will frequently fluctuate and lead to voltage flash.The change and characteristics above will change the running state of the network. So this paper analyzed the running state by taking account of power over-voltage, resonance over-voltage and voltage flash, and propounded the strategy that voltage flash were controlled by using Static var compensator (SVC).The paper discussed the power over-voltage of the network through central parameter equivalence circuit and distribution parameter equivalence circuit. And analyzed the resonance over-voltage with a typical power-distribution-net model, the result showed that cable length and load value could avoid the resonance over-voltage.The adverse effects of capacitor about voltage flash was discussed in this paper, and attested that fixed capacitor compensation add the voltage flash.The paper propounded that used the SVC to control voltage flash of the network. SVC is a new var generator based on the electric power and electronic technology, which can realize the dynamic var compensation and speed is quick. By simulating, this paper compared the effect of capacitor compensation to that of SVC compensation, the results showed that capacitor compensation add the voltage flash, and SVC was the optimal equipment to restrain the flash. Furthermore, the smaller value of Ks and Tf, the better effect of SVC.
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