保定市伊诺尔电气设备有限公司

1.控制电缆金属屏蔽的接地方式，应符合下列规定： 

1. metal shielding control cable grounding, shall comply with the following provisions:

    ①. 计算机监控系统的模拟信号回路控制电缆屏蔽层，不得构成两点或多点接地，应集中式一点接地。

1. Analog signal loop of computer monitoring and control system of control cable shielding layer shall not constitute two or more points should be centralized grounding, grounding point.

    ②. 集成电路、微机保护的电流、电压和信号的电缆屏蔽层，应在开关安置场所与控制室同时接地。

. the cable shielding layer of integrated circuit, microcomputer protection and current and voltage signals, should be in place and at the same time switch control room ground.

    ③. 除上述情况外的控制电缆屏蔽层，当电磁感应的干扰较大时，宜采用两点接地；静电感应的干扰较大时，可采用一点接地。双重屏蔽或复合式总屏蔽，宜对内、外屏蔽分别采用一点、两点接地。

. the control cable shielding layer in addition to the above, when the electromagnetic induction interference is larger, should adopt two grounding points; electrostatic induction interference is large, the grounding point. Double shielding or composite shielding, the internal and external shielding should be used one point and two points respectively.

     ④ .两点接地的选择，还宜在暂态电流作用下屏蔽层不被烧熔。 

4. Two point to ground, also should be shielded in the role of transient current layer is not melted.  

     ⑤. 强电控制回路导体截面不应小于1.5mm2，弱电控制回路不应小于0.5mm2。

The electrical circuit control section. The conductor shall not be less than 1.5mm2, the weak control loop should not be less than 0.5mm2.

2.控制电缆金属屏蔽为什么要接地： 

Why should the metal shielding control cable grounding: 2.

      金属屏蔽层最在电缆屏蔽接地是为防止电气设备因受电磁干扰造成误动和危害，为避免电磁干扰，控制电缆的屏蔽层均应接地。

Metal shielding layer in the cable shield grounding is to prevent electrical equipment due to electromagnetic interference caused by misoperation and harm, to avoid electromagnetic interference, shielding control cable shall be grounded.

屏蔽电缆的屏蔽层两端接地使电磁感应在屏蔽层上产生一个感应纵向电流，该电流产生一个与主干扰相反的二次场，抵消主干绕场的作用，显著降低磁场耦合感应电压，可将感应电压降到不接地时感应电压的1%以下。当然屏蔽电缆的屏蔽层两端接地也存在以下两个情况：

The shield cable shield grounded at both ends of the electromagnetic induction to generate an induction current in the longitudinal shielding layer, the current one opposite the main interference in the two field, the main offset around the field effect, significantly reduce the magnetic field induced voltage, the induced voltage drop to ground when the induction voltage of 1% the following. Of course, there are two cases in which the shielding layer of the shielded cable is grounded at both ends.

      ①、当接地网上出现短路电流或雷击电流时，由于电缆屏蔽层两点的电位不同，使屏蔽层内流过电流，会引起额外的冲击或干扰电压。

1, when the ground appeared on the short circuit current and lightning current, the potential of two different cable shielding layer, the current flowing through the shielding layer, can cause shock or additional disturbance voltage.

      ②、当屏蔽层内流过电流时，对每个芯线将产生干扰信号。但对应用于继电保护和自动装置回路的屏蔽电缆，由于其输入和输出均有一端在电网的高压或超高压环境中，电磁干扰是主要因数，为防止暂态过电压，故电气继电保护和自动装置的电缆屏蔽层宜在两端接地。

II, when the current flowing through the shielding layer, will produce interference signals on each core wire. But the shielded cable applied to relay protection and automatic device circuit, as its input and output are at one end of the power grid high voltage or extra high pressure environment, electromagnetic interference is the main factor to prevent transient overvoltage, the cable shielding layer of the electric relay protection and automatic device should be grounded at both ends.

二、高压电缆接地

Two. High voltage cable grounding

1.高压三芯电缆接地：35kV及以下电压等级的电缆都采用两端接地方式，这是因为这些电缆大多数是三芯电缆，在正常运行中，流过三个线芯的电流总和为零，在铝包或金属屏蔽层外基本上没有磁链，在铝包或金属屏蔽层两端就基本上没有感应电压，所以两端接地后不会有感应电流流过铝包或金属屏蔽层。

1. high voltage three core cable: cable of 35kV and below voltage are used at both ends of grounding mode, this is because most of these cables is three core cable, in normal operation, the total current flowing through the wire core three is zero, no magnetic chain basically in aluminum package or a metal shielding layer, in aluminum clad metal shielding layer or two ends basically no induction voltage, so there will be a parallel induction current flowing through the aluminum package or metal shielding layer.

2.高压单芯电缆接地：电缆在带负荷运行时，在屏蔽层会形成感应电压，如果两端的屏蔽同时接地，在屏蔽层与大地之间形成回路，会产生感应电流，这样电缆屏蔽层会发热，损耗大量的电能 ，影响线路的正常运行，当电缆线路发生短路故障、遭受雷电冲击或操作过电压时，屏蔽上会形成很高的感应电压。将会危及人身安全，甚至可能击穿电缆外护套。为了避免这种现象的发生，通常采用一端接地的方式，护套中就没有电流通过。但是，感应电压与电缆长度成正比，当电缆线路较长时，过高的护套感应电压可能会危及人身安全，并可能导致设备事故，因此，电缆运行规程规定，单芯电缆金属护套感应电压不得超过50V。对于较长的电缆线路，应用绝缘接头将金属护套分隔成多段，使每段的感应电压限制在小于50V的安全范围以内。通常将三段长度相等或基本相等的电缆组成一个换位段。

2. high voltage single core cable: cable to run with a load, an induced voltage in the shielding layer, if both ends of the shielding and grounding loop formed between the shielding layer and the earth, will produce induced current, so the cable shielding layer may have a fever, large consumption of electric energy, affect the normal operation of the line and when the cable line fault, suffered from lightning or switching over-voltage, shielding will form a high voltage induction. It will jeopardize personal safety and may even break through the outer sheath of the cable. In order to avoid this phenomenon, it is usually used in one end to ground, and there is no current in the sheath. However, induction voltage and cable length is proportional to, when the cable line is longer, the high voltage induction sheath may endanger the personal safety, and may cause accidents, so the operation rules of single core cable, cable metal sheath voltage shall not exceed 50V. For longer cable lines, the insulation joint is used to separate the metal sheath into multiple segments so that the induction voltage of each section is limited to less than 50V. A transposition section is usually composed of three segments of equal or basically equal length.

注：高压单芯电缆在制作电缆头时必须将钢铠和铜屏蔽层分开焊接接地，这样做的目的是为了便于检测电缆内护层的好坏，在检测电缆护层时，钢铠与铜屏蔽间通上电压，如果能承受一定的电压就证明内护层是完好无损。如果无需检测电缆内护层，可以将钢铠与铜屏蔽层连在一起接地（建议分开引出后接地）。

Note: the single core power cable in the production of cable head must be separated from the steel armor and a copper shielding layer welding, the purpose of doing so is to have the protective layer to facilitate testing cable, in the detection of cable sheath, steel armor and copper shield between the voltage, if can withstand voltage proof the inner layer is intact. If there is no need to check the cable sheath, steel armor can be connected together with copper shielding layer grounding (earthing should be separated after the lead).