变电站二次电缆屏蔽层接地方式探讨

变电站二次电缆屏蔽层是提高变电站电磁兼容水平的重要措施。二次电缆的屏蔽层采用1端接地还是2端接地目前仍然是一个有争议的问题。文章从抗干扰和防止过电压的角度分析了屏蔽层的作用，认为采用2端点接地后屏蔽层中流过的电流应分为感应电流和噪声电流。感应电流是由外界电磁场感应产生的，其实际作用是抵消外界电磁场的干扰。屏蔽层中的噪声电流对芯线干扰很小。屏蔽层1点接地情况下由于无电流回路，因而屏蔽层无法取得良好的屏蔽效果。在一个良好的接地网中采取均压、分流配套措施后，屏蔽层再采用2端接地则会具有更好的防止电磁干扰的效果，且屏蔽层很难发生烧毁事故。

DISCUSSION ON SHIELDED GROUNDING MODE OF CABLES IN SECONDARY CIRCUITS OF SUBSTATIONS

The shield of the cables in secondary circuits is an important measure to improve the EMC level of substation and it is still a controversial issue in the adoption of oneterminal grounding or both terminals grounding of the cable shield. From the viewpoint of anti-interference andover-voltage protection the action of cable shield is analyzed and it is considered that under the both terminal grounding the current in the shield of the cable consists of induction current induced by external electromagnetic field and noise current. The induction current can counteract the interference fromexternal electromagnetic field and the noise current can only cause slight interference in the core of the cable. When the shield is grounded at one terminal, because of the fact thatthere is no current loop only weak shielding effect can beachieved. In a well grounded network if the measures such as voltage equalizing and shunting is adopted, the two terminals of each cable should be grounded to obtain a better effect of preventing electromagnetic interferences. Besides, it is rare to burn the cable shield with both terminals grounded.