For a typical radiation type 220-110-10kV grid, the neutral point of the 110kV side transformer is a direct grounding system, but not the neutral point of each transformer is directly grounded. If the ground fault occurs on the 110kV transmission line, the neutral point voltage of the 110kV transformer will rise. Even the neutral point voltage breakdown will happen. This article will draw out the sequence network including photovoltaic power and calculate formula of distributed power and network voltage theory. Aiming at the typical power grid, respectively the main changes from the neutral breakdown occurred will be discussed at the same time. By analyzing the formula, the main factors affecting the voltage are obtained. The conclusion is of practical value. At the same time, the accuracy of the conclusion is verified by PSCAD simulation. The distributed power and the operation of point voltage are compared considering work condition of the main transformer.#$NLKeywords: asymmetric faults, distributed power supplies, neutral point voltage breakdown, point of common coupling