The main measures for control cables to prevent or reduce electrical interference include the following three aspects:

1. A spare core of the control cable is grounded

Practice has proved that when the spare core wire in the control cable is grounded, the amplitude of the interference voltage can be reduced to 25% to 50%, the cost of the cable will not increase too much, and the operation is simple.

2. Control cables must not be used in circuits that may cause severe electrical interference

The utility model includes: (1) a weak current signal control circuit and a strong current signal control circuit. (2) Low-level and high-level signal circuits; (3) The same control cable must not be used at each stage of the AC circuit breaker breaking process.

3. Metal shielding and shielding layer grounding

Metal shielding is an important measure to weaken and prevent electrical interference, including full shielding, sub-shielding and double-layer full shielding. The selection of metal shielded control cables should be based on the anti-interference ability and electrical potential of the cable, including comprehensive measures to reduce interference to meet the requirements of reducing interference and voltage. The anti-interference requirements are high and the investment is large. When the steel tape armored steel wire braided shield is full, the price of the cable drops by 10% to 20%.

For the control interference in the strong current loop, due to its strong signal, the control cable without metal shield can be selected except in the ultra-high voltage power distribution device or close to and parallel to the high voltage cable. When the control cable used in the weak current signal control circuit is located in an environment affected by interference, and there is no effective anti-interference measure, the control cable with metal shield should be selected to prevent electrical interference from causing misoperation or misoperation of the low-level signal circuit. Insulation breakdown.

The selection principle of the shielding type of the control cable of the signal loop of the computer monitoring system is as follows:

(1) Switch signal, which can be shielded;

(2) For advanced analog signals, the overall shielding of the cores should be used, and the secondary shielding of the cores can also be used if necessary;

(3) For low-level analog signals or pulse signals, it is better to use the secondary shielding of the wire core, and if necessary, you can also use the composite overall shielding with the secondary shielding of the wire core.

The following points should be noted in the grounding method of the shielding layer:

(1) The shielding layer of the control cable of the analog signal circuit of the computer temporary control system should be grounded at one point. The reason is based on the requirement to ensure the normal operation of the computer monitoring system, because even if the interference voltage is only about 1V, it may lead to errors in logical judgment. Centralized grounding can avoid grounding loops;

(2) Except that the shielding layer of the control cable of the computer monitoring system is only allowed to be grounded at one point, the shielding layer of other control cables shall be grounded at two points when the electromagnetic induction interference is large, and shall be grounded at one point when the electrostatic induction interference is large ;

(3) The inner shielding layer of double shielding or composite full shielding should be grounded at one point, and the outer shielding layer can be grounded at two points;

(4) When choosing two-point grounding, it should also be considered that the shielding layer will not be burnt under the action of transient current.