In the electrical industry, mastering the basics is just the beginning. True expertise lies in understanding the nuances of modern materials, the precision of mechanical installation, and the specific standards that ensure safety and longevity. Following our previous discussions on cable types and pre-installation checks, this edition dives into advanced topics—from the superiority of heat-shrink accessories to the meticulous process of terminating a 10kV cable.
Here are the answers to the next set of critical field questions.
21. What are the advantages of Cross-Linked Heat-Shrink Cable Accessories?
Heat-shrink technology represents a significant leap forward in cable joining. Compared to traditional options, these accessories offer:
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Superior Electrical Performance: Excellent dielectric properties.
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Compact & Lightweight: Reduced size and weight simplify handling and space management.
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Ease of Installation: Simplified construction process with配套 (matched) material kits.
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Environmental Resilience: High resistance to weather, pollution, and chemicals, coupled with flame-retardant and self-extinguishing properties.
22. What are the mechanical strength requirements for conductor connections?
A connection is often the weakest point in a circuit. To ensure reliability:
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The mechanical strength of a connection point is typically lower than the conductor itself.
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For fixed power cables, the tensile strength of the joint must be no less than 60% of the conductor's own tensile strength.
23. What are the essential properties of cable insulation materials?
The insulation is the heart of the cable. It must possess:
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High Breakdown Strength: To resist electrical puncture.
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Low Dielectric Loss: To minimize energy waste as heat.
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High Insulation Resistance: To prevent leakage current.
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Excellent Discharge Resistance: To withstand corona and partial discharges.
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Mechanical Flexibility: To endure bending during installation.
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Long-Term Stability: Maintaining performance over decades of service.
24. What are the traction strength limits during mechanical cable pulling?
Pulling too hard damages the conductor. Follow these strict limits:
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Copper Core (Head Pulling): Max 70 N/cm
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Aluminum Core (Head Pulling): Max 40 N/cm
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Lead Sheath (Wire Mesh Pulling): Max 10 N/cm
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Aluminum Sheath (Wire Mesh Pulling): Max 40 N/cm
25. What are the rules for cable protection conduits?
When running cables through pipes, adhere to these specifications:
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Inner Diameter: Must be at least 1.5 times the cable's outer diameter. For concrete, ceramic, or asbestos-cement pipes, the minimum ID is 100mm.
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Bend Radius: The pipe's bend radius must match or exceed the cable's minimum bending radius.
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Bends: Limit to three bends per conduit, with no more than two 90-degree bends.
26. How do you accurately measure cable jacket diameter?
Precision matters for calculating pull tensions and clearances. Measure the jacket circumference at five evenly spaced points around the circle. Calculate the average of these five measurements to determine the official outer diameter.
27. How do you connect copper cables with different cross-sections?
Transition joints require special care:
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Method A: Use an open-back (split-barrel) copper connector and secure it using the tin-soldering method.
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Method B: Machine a custom copper connector from a pure copper rod to match the two different diameters, then secure it using the crimping method.
28. Walkthrough: Making a 10kV XLPE Heat-Shrink Indoor Termination
This is a high-precision task requiring a clean environment:
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Prep: Verify all components and check the cable for moisture.
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Cut: Trim the cable to the required length.
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Strip: Remove the outer sheath and shielding layers carefully.
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Ground: Solder the ground wire to the steel tape armor.
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Seal: Fill the "crotch" (where three cores separate) with sealing mastic.
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Branch: Slide the three-core stress control tube over the base and shrink from the center out.
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Clean: Strip back the copper tape and remove the semi-conductive layer (do not nick the insulation).
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Stress Control: Install and shrink the stress relief tubes.
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Terminate: Crimp on the terminal lugs.
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Insulate: Slide and shrink the main insulation tubes over the cores.
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Weatherproof: Install the weather/anti-tracking sealant tubes.
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Finish: Perform phase identification and install the colored phase sleeves.
29. Steps for Installing Indoor/Outdoor Premolded Terminations
Premolded terminations offer speed and consistency:
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Position and clamp the cable. Clean the surface thoroughly.
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Strip the outer sheath according to the manual; typically, leave 20mm of copper tape and prepare grounding leads for both the shield and armor.
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Measure the required length from the sheath edge, trim excess cable, and slide on the premolded stress cone/sleeve.
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Crimp the terminal lug and apply the final sealing mastic or heat-shrink covers.
