Research On Effect And Improvement Strategy Of Photovoltaic Power Generation Grid Connection On Distribution Network Protection

In recent years, as the development of researches on solar cells and related technology, photovoltaic power generation, as one kind of new energy, is under large scale construction year after year. Besides, an increasing number of photovoltaic power stations are put into operation and connected into domestic power grid in China. After power circuits break down, the photovoltaic power generation system will have an influence on relay protection and automatic recloser, especially on three phase current protection based on breaker, which will lead to sensitivity decline, refusing action, false action and selective failure of grid connection circuit protection. At the same time, it will affect the correct operation of automatic safety device, like non-voltage criterion of auto-switching devices, failure operation of back-up power and so on.At first, this paper presented the principle of power grid relay protection and its characteristics and setting principles. Common spare power automatic switching strategies of power grid were introduced as well. Based on that, the influence of photovoltaic power grid connection on protection relay and automatic safety devices were researched systematically. The influence of different connection strategies of photovoltaic power on relay protection and automatic safety devices were analyzed. The problems caused by photovoltaic power grid connection on grid protection were analyzed. This paper also analyzed the effects of photovoltaic power on spare power automatic switching and the malfunction of spare power possibly caused by it. Besides, this paper analyzed the problems of spare automatic switching non-voltage criterion caused by photovoltaic power.Aiming at the photovoltaic power grid connection’s influence on grid protection, this paper provided circuit current protection strategies of grid connection. By using the strategies of power direction, low frequency protection, non-voltage detection recloser strategy was proposed for traditional three-phase one-shot recloser. For the effects of starting failure when non-voltage tripping out, a zero sequence voltage protection strategy by adding transformer neutral point was proposed. In order to preventing the failure of non-voltage breaking off protection, a protection strategy of adding the neutral point of transformer was taken to disconnect all the breakers connected with power source. A low-frequency criterion condition was also used in secondary starting circuit. Reverse power supply was avoided by the combination of the two protection strategies as an OR relationship. In order to prevent asynchronous reclosing, a strategy of connecting in series photovoltaic power contact breakers’ assisting junction in the control circuit of automatic switching devices was proposed. In the case of Miyun photovoltaic power generation grid connection construction, the researching result was verified in terms of feasibility and rationality.