Safety is our top priority at Ningbo Changshi. The best practices for underground cable laying include a multi-faceted approach. First, thorough pre-installation planning is crucial, including a comprehensive utility detection and mapping process using advanced equipment. Second, proper trench design with appropriate depth, width, and shoring is essential to prevent cave-ins. Third, using the correct Personal Protective Equipment (PPE), such as insulated gloves and hard hats, is non-negotiable. Finally, and most importantly, employing specialized equipment like our high-quality cable rollers and pulling machines ensures cables are laid without undue strain or damage, enhancing both worker safety and the integrity of the cable. Our company offers a full range of equipment to facilitate these best practices.

Answer: Choosing the right tools is critical for a safe and efficient cable pulling project. Key considerations include:

1. Cable Pulling Winches/Tensioners: Ensure the equipment has the correct pulling force and tension monitoring capabilities for your specific cable type and project requirements. Our hydraulic puller-tensioners offer precise control.

2. Cable Rollers and Sheaves: These are essential for guiding and supporting cables, minimizing friction, and preventing damage. We offer a variety of high-strength rollers for different applications, including straight and corner rollers.

3. Cable Pulling Accessories: Use appropriate cable lubricants to reduce friction and pulling grips/socks to securely attach to the cable without causing damage. Our accessories are designed to work seamlessly with our equipment for a smooth installation.

Proper installation is critical for an effective grounding system. Key best practices include:

1. Use Quality Materials: Always use high-quality, corrosion-resistant materials, such as copper-bonded steel earth rods and copper conductors, which are proven to withstand environmental stresses.

2. Proper Sizing: The grounding cable must be correctly sized to handle the maximum expected fault current.

3. Secure Connections: All connections must be tight and secure to ensure low resistance. We highly recommend using exothermic welding, which creates a molecular bond for permanent, low-resistance connections that are superior to mechanical clamps.

4. Regular Testing: Periodically test the resistance of the grounding system to ensure its integrity and effectiveness over time.

The pulling process requires careful planning and the use of specialized equipment to prevent damage to the cable's insulation and sheath.

• Pulling Tension: Always calculate the maximum allowable pulling tension and use a hydraulic cable puller with a tension recorder to ensure this limit is never exceeded.

• Minimum Bending Radius: Adhere strictly to the manufacturer's specified minimum bending radius to avoid mechanical stress on the cable. Use appropriately sized cable rollers and sheaves, especially at bends and corners.

• Lubrication: Use a manufacturer-approved, high-quality cable pulling lubricant to reduce friction and minimize pulling tension.

A well-designed grounding system serves two primary functions:

1. Personnel Safety: It provides a low-resistance path for fault currents to safely dissipate into the earth, preventing dangerous electric shocks.

2. Equipment Protection: It stabilizes voltage, dissipates lightning strikes and other surges, and prevents costly damage to sensitive electrical equipment.

By providing a reliable path for excess current, a good grounding system ensures that protective devices, such as circuit breakers, can operate correctly and quickly to clear a fault.

Jointing and termination are critical interfaces and potential points of failure.

• Skilled Technicians: These tasks must be performed by highly skilled and certified jointing technicians with specific experience in 66 kV cable systems.

• Quality Accessories: Only use high-quality, pre-tested, and type-approved cable accessories, such as heat-shrinkable or cold-shrinkable joints and terminations.

• Controlled Environment: The work must be carried out in a clean, dust-free, and moisture-controlled environment to prevent contamination that could lead to electrical failures.

While underground lines are more reliable, their installation and operation present specific challenges at the transmission level:

• Heat Dissipation: At EHV levels, the cables generate immense heat. Unlike overhead lines that are air-cooled, underground cables rely on the surrounding soil to dissipate heat. Special thermally conductive backfill materials must be used to prevent the insulation from overheating and failing.

• High Pulling Tension: The sheer weight of a long, heavy transmission cable means that immense pulling force is required. This necessitates professional-grade hydraulic cable pullers that are capable of delivering several tons of controlled tension without damaging the cable's sensitive core.

• Cable Joints and Terminations: These are the most vulnerable points in an underground transmission system. Splicing a 230kV cable is a highly specialized task that must be performed in a clean, controlled environment to prevent voids and contaminants that could lead to electrical breakdown.

• Capacitive Effects: Unlike overhead lines, underground cables have a high capacitance, which can create a voltage rise along the line. This requires expensive and complex reactive compensation equipment to manage and maintain stable grid voltage.

The laying of 11 kV underground cables is a multi-step process that requires careful planning and execution. The procedure typically includes:

• Route Survey and Planning: Identifying the precise cable route, avoiding other utilities, and conducting a geotechnical survey to assess soil conditions.

• Excavation and Trenching: Digging a trench according to specified dimensions and safety standards.

• Cable Laying: Using specialized equipment like cable drum jacks, rollers, and winches to lay the cable smoothly into the trench.

• Backfilling and Protection: Covering the cable with a protective layer of fine sand or thermal backfill, followed by brick or tile protection, and then restoring the trench.

• Jointing and Termination: Connecting cable sections and terminating them at switchgear or transformers.

• Testing and Commissioning: Performing insulation resistance, continuity, and high-voltage tests to ensure the integrity of the installed system.

Successful installation of an underground transmission line hinges on the use of specialized, heavy-duty equipment. Our product line is specifically designed to meet these challenges:

• Hydraulic Cable Pullers: Our EHV pullers are equipped with real-time tension monitoring to ensure the cable's maximum pulling tension is never exceeded.

• Hydraulic Drum Stands & Trailers: Given the immense weight of transmission cable reels (often exceeding 20 tons), hydraulic drum stands are essential for safe and controlled unwinding.

• Heavy-Duty Cable Rollers: These rollers are designed to support the immense weight of EHV cables and maintain the specified minimum bending radius at all turns, reducing friction and protecting the cable's outer sheath.

• Duct Rodders: These tools are used to push a pilot line through the conduit before the main cable pull, ensuring the path is clear and ready.

Trench specifications are critical for the thermal performance and mechanical protection of the cable. The standard trench depth and width depend on local regulations and the number of cables. For a single circuit, a common depth is around 1 meter.

• Backfill Material: To ensure proper heat dissipation, a layer of fine sand or a purpose-designed thermal backfill is used directly around the cables. This material has low thermal resistivity, preventing the cable from overheating.

• Protection: After the initial backfill, a layer of protective tiles or bricks is laid to serve as a physical barrier against future excavation damage.

A professional electrical underground construction project is a multi-phase endeavor that requires meticulous planning and precision at every step. The process is broken down into the following key phases:

1. Planning and Surveying: Before any digging begins, a thorough site survey is conducted to map out the exact route and identify existing underground utilities using specialized locators. Engineers determine the appropriate trench depth, cable specifications, and the necessary equipment. This phase also includes obtaining all required permits and ensuring compliance with local codes.

2. Trenching and Conduit Installation: This phase involves excavating a trench along the planned route. For most projects, a protective conduit is laid inside the trench. This conduit is essential as it shields the cables from physical damage and moisture and simplifies future repairs or upgrades.

3. Cable Pulling or Blowing: This is the core installation step where the power cables are deployed into the conduit. A hydraulic cable puller is used to apply a smooth, controlled force to pull the cable through the conduit over long distances. For certain applications, a cable blowing machine can be used to push the cable with compressed air, which is highly efficient for specific types of cables and routes.

4. Splicing and Termination: Once the cable is in place, skilled technicians connect sections of the cable with specialized joints (splices) and connect the ends to transformers, switchgear, or other equipment with terminations. This work is highly technical and critical to the integrity of the entire system.

5. Testing and Backfilling: The completed system is rigorously tested using diagnostic equipment to confirm that there is no damage or signal loss. Once testing is complete, the trench is backfilled with a protective layer (often sand) and then the excavated soil, which is compacted to prevent future ground settling.

Managing pulling tension is crucial to avoid damaging the cable's inner conductors or insulation. We recommend the following:

• Pulling Force Calculation: The maximum pulling tension is calculated based on the cable's size, material, and route. This value must not be exceeded.

• Hydraulic Pullers: Using hydraulic cable pullers equipped with tension recorders ensures a controlled, constant pull and provides a real-time record of the force applied.

• Specialized Equipment: Cable rollers are used at regular intervals to reduce friction, and guide sheaves are installed at bends to maintain the minimum bending radius and prevent excessive sidewall pressure.

• Swivels and Grip: A pulling swivel should be used between the pulling rope and the cable grip to prevent twisting.