Cross-linked cables typically refer to cables where the insulation is made from cross-linked materials, with the most common being cross-linked polyethylene (XLPE). This material is created by transforming the linear molecular structure of polyethylene (PE) through a specific processing method, resulting in a three-dimensional network structure. This transformation significantly enhances the cable’s thermal performance, raising the long-term allowable operating temperature from 70°C to 90°C or higher, and increasing the short-circuit temperature resistance from 140°C to 250°C or more. As a result, the cable maintains its excellent electrical properties under more demanding conditions.
**Identifying False Breakdowns in Cross-Linked Cables:**
During partial discharge and high-voltage testing of medium-voltage cross-linked power cables using a series resonance test system, false breakdowns can occur due to various reasons. Accurately distinguishing between a real breakdown and a false one is crucial for improving the efficiency of factory testing.
These tests are usually conducted in a shielded room, with each section tested individually. If a core passes the test after replacement, it suggests that the original cable may have had an issue. If the breakdown voltage gradually decreases, this could indicate a real fault in the cable. However, if the breakdown voltage remains constant, it might point to a breakdown at the end of the cable. At this stage, manually closing the partial discharge switch and opening the shielded room door can help observe the breakdown and quickly locate the fault. If no breakdown occurs at the end, replacing multiple insulated cores or retesting the cable—either with a load or without—can help confirm whether the issue was a false breakdown. If the voltage remains consistent, it's likely a false reading, and the equipment should be checked before further troubleshooting.
For longer single-core medium-voltage cables, it's also important to check if the test equipment is within its capacity. If the system detunes during the test, it shouldn’t be immediately assumed that the cable has failed. There are also special cases where internal insulation may short-circuit, causing the series resonance system not to reach the resonant step. In such cases, simply replacing the faulty core with a good one for testing can confirm the issue.
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