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Several issues that should be paid attention to when selecting and using control cables

Update:2021-06-25
Abstract:

1. Overview of control cables The cables connected from […]

1. Overview of control cables
The cables connected from the control center to various systems to transmit signals or control operating functions are collectively referred to as control cables.

2. Main series of control cables
The main products of today's control cables are: PVC insulated control cables, natural styrene butadiene rubber insulated control cables and polyethylene insulated control cables.

3. Measures to ensure the normal operation of the control cable and prevent interference
"Power Engineering Cable Design Specification" stipulates: current, voltage, DC cable with plug and trip control. Two sets of dual protection circuits that require enhanced reliability should use separate control cables.

After the control cable is put into use, there will be problems of electrical interference between different cores of the same cable and between cables placed parallel to each other. The main causes of electrical interference are: (1) Capacitive coupling between cores due to applied voltage.
(2) Electromagnetic induction interference caused by energized current. Generally speaking, when there is a high-voltage and large-current interference source nearby, the electrical interference will be more serious.

For example, in the control circuit of a high-voltage substation for split-phase operation of circuit breakers, a single cable is used in combination of three phases. Such an accident happened. The pulse of the split-phase operation causes the thyristors of the other phases to trigger, which leads to the misconnection of the three phases. Using a separate cable, there will be no misoperation accidents again. Another example is the computer monitoring system of a power plant. Due to the use of a four-core cable to combine the analog low-level signal line with the power line of the transmitter, an interference voltage of 70V was once generated on the signal line, which was measured in millivolts. The low-level signal loop obviously affects normal operation.

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