城市微网接地方案探讨

针对低压微电网在不同接地方式下运行的安全稳定性问题,提出了典型微网的接地方案。基于国家/行业标准,结合理论分析和实践应用比较,对低压微电网主变压器接地方式、微源接地方式、低压微网系统接地方式分别进行了比选,给出了不同情况下各种接地方式的适用条件和场合。结合微网系统特点得出了适用低压微网的接地方案,即主变优选用D,yn11连接组别,中性点有效接地,微源并网时中性点不接地,孤岛时仅主电源中性点接地。整个微网系统采用TN-S/TN-C-S与TT混合接地方式,微源和三相用户采用四级开关,单相用户采用两级开关。

Study on grounding arrangement of microgird of city

Different grounding modes in low-voltage microgrid bring a series of security and stability issues. To solve these problems, a grounding arrangement for low-voltage microgrid is proposed. With deeply researching national standards and electric standards, combined with the analysis of theory and application, the grounding modes of the main transformation, distributed generation and low-voltage microgrid system are compared respectively, and applicable condition and occasion of various grounding modes in different circumstances are given. Finally, grounding arrangement in the classical microgrid is given by contacting with character of the microgrid, i.e. the main transformer selects D, yn11 connecting group grade preferentially with neutral grounding. The neutral points of distributed generations are ungrounded when microgrid is on-grid, and only the neutral point of main distributed generation turn into grounded when microgrid is off-grid. The whole microgrid system adopts mixed grounding mode with TN-S, TN-C-S and TT by applying four-grade switch for distributed generations and three phase loads and two-grade switch for single phase loads.