Abstract:

In distribution networks in a non-ground neutral system, the phase-mode transformation theory was used to get the 0-mode equivalent network system, and the inner reasons of the over caused potential transformer (PT) ferroresonance were studied. Then, the mathematical model of the 0-mode network was established based on the theory of time-varying vector, according to which the curve of ΔI(φL) was obtained. Through the analysis of the curve the results showed that the existence of the system steady-state resonant point was the reason that caused the occurrence of ferro-resonance. Finally, according to the size of the disturbance, the concept of speed up energy and slow energy was put forth based on the Lyapunov energy function, and the judgment system steady-state resonance standards, such as the happened-area of law was also given. Alternative transient program(ATP) simulations showed that the forward theory was efficient. The analysis of the distribution network PT accidents and subsequent inhibit burn out could provide an important theoretical basis for the research work of ferro-resonance.

Key words: potential transformer (PT), ferro-resonance, over-voltage, time-varying vector