关于中性点电位偏移的分析与防护

Analysis of the Offset of the Neutral Point’s Electric Potential and It’s Pretection

分析了三相四线制供电系统中,中性点电位偏移的原因、后果及防护措施.当三相负载不平衡度达到一定值时,中性线一旦断开,则中性点电位偏移电压(UN'N)将大于50V;与之相对应的三相负载相电压过、欠电压值将达额定值的20%以上,危及用电设备和人身安全.本文在综合分析的基础上,介绍一种新型“过、欠电压型”中性线断线保护器的原理、特点及应用,它与原有的“电压型”中性线断线保护器不同,避开了原来以UN'N为取样值需单独设置工作接地的难题,具有新颖、实用的特点.

The paper point out how the offset of the neutral point＇s electric potential is formed and what it will be result and what is the protective measure in three -phase four-wire system .When the three-phase loads are not the same seriously the neutral point＇s electric potential will exceed 50V and at the same time the three-phase load voltages will be over or under 20% of the rated value if the neutral conductor is broken. In this situation the electric equipment can be damaged or can not work .And the safety of people is endangered. On the basis of analysis the paper introduces the principle, the characteristics and the applications of a new kind of neutral conductor interrupted protective equipment with “over or under bias -voltage mode” .It is deferent from the old one with “voltage mode”. It is also avoid the difficult problem of the old one which needs an alone grounding for getting the sample voltage UNN. It is new ; besides, it is useful indeed.