What issues should be noted when using control cables?
Release date:
2022-11-17 11:12
Source:
Control cable These are cables that connect from the control center to various systems, used to manage operational functions or transmit signals. Early control cables primarily handled tasks such as operating relays and switching devices, powering instrument indicators, illuminating indicator lights, and managing alarm interlock systems—functions that were relatively simple. In recent years, however, with the widespread adoption of computer networks and low-voltage electrical systems, new demands have emerged, placing higher and more sophisticated requirements on the selection and application of control cables.
The main series of control cables currently includes natural styrene-butadiene rubber-insulated control cables, polyvinyl chloride-insulated control cables, and polyethylene-insulated control cables. Additionally, there are also ethylene-propylene rubber-insulated and cross-linked polyethylene-insulated products available.
Currently, our country can still produce 600/1000V plastic-insulated control cables, while rubber-insulated control cables have a rated voltage of 300/500V. The conductors in these control cables are made of copper, with nominal cross-sectional areas of 2.5mm² and below—ranging from 2 to 61 cores—and for larger sizes, 4 to 6mm² with 2 to 14 cores, and 10mm² with 2 to 10 cores. The operating temperatures for control cables are as follows: polyvinyl chloride (PVC)-insulated cables come in two grades—70°C and 105°C—while rubber-insulated cables operate at 65°C. Typically, PVC, PE, XLPE, and fluoroplastic-insulated products are used as control cables for computers.
The state mandates that dual protection systems—such as current-voltage systems, DC power supplies, and trip-control circuits—must each be equipped with their own set of control cables. This measure is designed to ensure that, in the event of mechanical damage, insulation breakdown, or fire, the impact on other parts of the system can be minimized. Once the control cables are put into operation, however, electrical interference issues may arise between different cores within the same cable, as well as between adjacent cables laid in parallel. The primary causes of these interferences include: 1) Electromagnetic induction interference caused by current flow. Generally speaking, when high-voltage, high-current sources are located nearby, the resulting electrical interference tends to be more severe. Since the core wires within a single cable are placed relatively close together, the level of interference is significantly greater compared to cables installed separately but running parallel to each other. 2) Electrostatic interference caused by capacitive coupling between cores due to external voltages. For instance, in high-voltage substations, control circuits for phase-operated circuit breakers often share a single cable across three phases. As a result, there was an incident where thyristors in one phase were inadvertently triggered by phase-operation pulses from the other phases, leading to unintended simultaneous operation of all three phases. After switching to independent cables, such erroneous operations no longer occurred.
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