基于DG并网变压器接地方式及相关零序保护方案选择

Abstract

越来越多的DG通过低压配网并网，如何选择一种可以不依赖于DG性质，并且运行方式可靠的保护方案是工程技术人员面临的一大问题。合理配置并网耦合点保护方案，不仅可以对系统故障进行及时判断，同时在DG孤岛时，在孤岛形成的动态过程及孤岛划分后的运行方式下仍旧保持保护特性，始终保持对孤岛内故障具有足够的选择性是本文着重解决的问题。本文通过对DG并网变压器接地方式的选择，分析出零序电流与零序电压的关系；通过优化保护方案，可实现抑制 DG并网及脱网运行时出现的零序过电压，还可以利用零序量当作故障时稳定判据，制定出了一整套针对DG并网变压器接地系统的保护优化方案。本文最后通过COBASE系统生成一个DG经低压并网的保护方案，验证其在并网及孤岛动态形成过程中的保护优良特性。 More and more DG is interconnected through the low voltage distribution network; how to choose a protection scheme which doesn’t depend on the nature of DG, and find a reliable operation mode are a big issue faced by engineers. The rational allocation of interconnection coupling point pro-tection scheme not only can judge the system fault in time, but also at the same time can maintain the protective properties in the dynamic process of the formation of island and after the operation mode of island division in DG Island. Always keeping the fault with sufficient selectivity within the island is the problem to be solved in this study. This paper analyzed the relationship between the zero sequence current and zero sequence voltage through the selection of the grounding method of the DG interconnection transformer; the optimization of the protection scheme can realize the inhibition of zero sequence over-voltage occurring in DG interconnection and running off network, and at the same time, it can work out a set of the protection optimization scheme in view of DG in-terconnection transformer grounding system by using the zero sequence quantity as a stable cri-terion at fault time. Finally, the protection scheme of DG low-voltage interconnection is generated by the COBASE system, which is proved to be of good quality in the process of interconnection and island formation.