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New method of core breaking for flame-retardant cable
With the rapid growth of China's economy, the cable industry has also experienced significant development. Cables come in various types depending on their intended use and performance characteristics. There are over 100 different kinds of cables, including computer cables, fire-resistant cables, and control cables. In recent decades, the production capacity of China’s wire and cable manufacturing sector has reached impressive levels. Within key industries such as electric power, rail transit, data communication, automotive, and mining, the scale of operations continues to expand, driving a growing demand for cables. As a result, the future of the cable industry in China looks promising, with plenty of room for further development.
However, during operation, cables can sometimes experience malfunctions, such as insulation breakdown, conductor damage, or core failure. For flame-retardant cables, the conductor often has a smaller cross-sectional area, making it more prone to breaking during the extrusion process. So, how can one detect a break in a flame-retardant cable?
**A: Power Capacitor Method**
Some cable manufacturers have used the capacitive comparison method in the past to locate the approximate position of a break. This involves applying continuous power to identify the fault point. However, this method is very inefficient, often taking about an hour and a half to locate a single break. Moreover, it is nearly impossible to detect a broken core in a finished flame-retardant cable that has already been shielded, armored, and jacketed. If the manufacturing process isn't done properly, the entire cable may be scrapped. As a result, this method is rarely used anymore.
**II: Combination of Capacitance Sensing and Inductive Voltage Method**
This approach is suitable for cables where the core is not covered by a metal layer and the outer sheath hasn’t been extruded yet. The process starts by using a capacitor to locate the general area of the break, followed by the induced voltage method to pinpoint the exact location. This technique is simple, fast, and widely used today. The inductive voltage method involves applying an AC voltage of 650V to one end of the broken core while grounding the other end and the remaining cores. A sensor pen capable of sending optical signals is then used to scan along the cable. When the sensor moves away from the broken section, the signal changes, allowing for precise identification of the break.
**III: Constant Current Source and Bridge Method**
This method is typically used for cables that have a metal layer covering the core or are fully coated. It involves using a constant current source to burn through the insulation at the broken point of the flame-retardant cable, after which a bridge fault locator is used to accurately identify the fault. This is another commonly used technique in the industry.