核电厂中压厂用电中性点不接地系统对地电容电流的研究

Research of Grounding Capacitive Current of Neutral Non-Grounding Auxiliary System in Nuclear Power Plants

在国内外标准中,不接地厂用电系统对地电容电流的限值数值为≤10 A。标准中限制电容电流是为了加快电弧熄灭,降低电弧过电压的持续时间,而并不是防止电弧的产生。电弧过电压的危害与过电压的倍数、发生频率和持续的时间有关。当系统设备存在绝缘薄弱点时,电弧过电压可能导致电气设备中绝缘薄弱点击穿,造成多点短路事故。电缆接头、附件以及电动机的绕组都是绝缘薄弱点。设置消弧线圈可中和系统的电容性接地电流,达到快速消弧的目的;使用浇注母线可显著降低输电线路的对地电容电流值,对设备更安全。

In the domestic and abroad standards, the grounding capacitive current limitation in the non-grounding electric auxiliary system is less than 10 A. Limiting capacitive current in the standard aims to speed up the arc extinguishing, to reduce the duration of arc over-voltage, but not to prevent the arc producing. The arc over-voltage harm is related to the multiple, frequency and duration of the over-voltage. When the insulation vulnerabilities appear in the 6quipment, the arc over-voltage may result in insulation vulnerabilities of the electrical equipment breakdown, which leads to multiple short-circuit accidents. The cable connector, accessory and electromotor winding are all insulation vulnerabilities. Setting the arc suppression coil which can counteract the grounding capacitive current makes the are vanish quickly. Using the casting bus which remarkably reduces the ground capacitance of the electric transmission line makes the equipment safer.