Answer: The most critical factor is tension control. Cables have a maximum tension and sidewall bearing pressure they can withstand. A suitable winch must be able to control tension precisely to prevent damage, especially around bends, where tension can increase exponentially. We at Ningbo Changshi offer a range of winches with advanced hydraulic controls and tension monitoring systems to ensure you never exceed the safe pulling limits of your cables.

Answer: The testing and commissioning phase is a crucial step to ensure the long-term reliability of an EHV cable system. This process typically involves a series of rigorous tests:

• Pre-Installation Checks: Verifying the cable's integrity before it is pulled, ensuring there is no damage from transportation or handling.

• Insulation Resistance Test: Using a megger to check the insulation resistance of the cable.

• Partial Discharge (PD) Test: This is a vital test for EHV cables. It detects any minute electrical discharges that could indicate a flaw in the insulation or jointing, which could lead to future failure.

• High Voltage AC/DC Withstand Test: Applying a high voltage to the cable for a specified duration to prove its ability to withstand operational voltage without breakdown.

Answer: For long or complex pulls, a key strategy is to use a winch in combination with a cable pusher or drum drive. These synchronized systems relieve back tension on the cable as it unwinds from the drum, significantly reducing the incoming tension before it hits a bend. This helps to control sidewall pressure and protects the cable from damage.

Answer: Electrical cable laying projects, especially those involving high and extra-high voltage lines, present several serious hazards. The most common include:

• Electrocution: The risk of accidental contact with energized lines is a primary concern. This can be prevented by ensuring a safe work clearance from existing power lines and strictly following lockout/tagout procedures before beginning work. Our overhead tools and accessories are designed to assist in maintaining safe distances and handling conductors with precision.

• Mechanical Damage: Cables can be damaged during pulling, tensioning, or installation, leading to potential future failure. To prevent this, it is essential to use equipment that provides controlled tension and pulling force. Our tension stringing equipment and underground cable laying equipment are engineered to apply precise, measured force, minimizing stress on the cable jacket and conductors.

• Falls and Falling Objects: Working at height on utility poles or towers poses a risk of falls. In addition, dropped tools or equipment can injure workers below. Mitigation involves using high-quality personal protective equipment (PPE), securing all tools with lanyards, and ensuring a designated safety zone around the work area.

Safety is paramount. Key best practices include:

• Regular equipment inspection: Check the winch, rope, and all accessories (like rollers and swivels) for any signs of wear before each use.

• Proper anchoring: Always anchor the winch to a stable point with an anchor weight at least twice the anticipated pulling tension.

• Adhering to safe working loads (SWL): Do not exceed the manufacturer's rated capacity for the winch or the cable's safe tension limits. For underground pulls, a 3:1 ratio of equipment break working load is a common practice, while for overhead lines, it's often 5:1.

• Using the right accessories: Employ high-quality cable rollers, swivels, and grips to minimize friction and prevent cable twisting or kinking.

Answer: Choosing the right equipment is one of the most effective ways to ensure safety and prevent accidents. High-quality tools and machinery from a reliable manufacturer like Ningbo Changshi are designed with safety as a top priority. Our equipment helps improve safety in several ways:

• Precision and Control: Our hydraulic pullers and tensioners allow for a smooth and controlled installation process, preventing sudden jerks or excessive forces that could lead to equipment failure or cable damage.

• Durability and Reliability: All our tools are manufactured to high standards, ensuring they can withstand the rigorous demands of power line construction. This reduces the risk of equipment malfunction or breakage during a critical phase of the project.

• Ergonomic Design: Many of our tools and accessories are designed to reduce physical strain on workers, helping to prevent injuries and maintain focus throughout long workdays.

While both perform a pulling function, they are designed for different applications. A winch for underground cable laying typically focuses on controlled, powerful pulling over a shorter distance through ducts and trenches, often with high friction points. In contrast, an overhead line stringing winch is designed to handle longer spans and different tensioning requirements, and may also be used for conductor recovery. Both require precise tension control, but the specific features and accessories, such as drum size, rope type, and capacity, are tailored to their respective environments.

Answer: The direct cable laying method is a common and cost-effective technique for installing underground electrical cables. In this method, the cable is placed directly into a trench that has been dug in the ground. The process is executed in several key steps:

1. Trench Excavation: A trench of a specific width and depth is dug along the planned cable route.

2. Cable Bedding: A layer of soft, fine material like sand or sifted soil is laid at the bottom of the trench to provide a protective, level bed for the cable.

3. Cable Laying: The armored cable is carefully laid on top of the bedding.

4. Backfilling and Protection: Another layer of sand is placed over the cable. A warning tape, clearly marked with "CAUTION: ELECTRICAL CABLE BELOW," is then laid to provide a visual warning for any future excavation work.

5. Final Backfill: The remainder of the trench is filled with the excavated soil, and the ground surface is restored.

This method is popular because it is simple and has a high heat dissipation rate, which is crucial for a cable's performance. Our specialized underground cable laying equipment ensures that this process is executed efficiently and with minimal stress on the cable.

Here is a diagram explaining the process:

The most common methods for installing 132kV underground cables are direct burial, laying in ducts or conduits, and laying in trenches. The selection of the method is a critical decision that depends on several factors, including:

• Location: Densely populated urban areas often require duct-laying to minimize disruption and allow for future maintenance without re-excavation. In contrast, direct burial is a cost-effective option for open areas.

• Soil Conditions: Direct burial is suitable for stable soil, while rocky or unstable ground may necessitate trenches or ducts.

• Environmental Impact: Trenchless methods like Horizontal Directional Drilling (HDD) are increasingly used to cross rivers, roads, or other obstacles to reduce environmental disturbance.

• Maintenance Requirements: Laying cables in ducts or troughs allows for easier repair, inspection, and future expansion.

Answer: The formation of cables refers to the physical arrangement in which single-core cables are laid in a trench. The two primary formations are trefoil and flat. The choice of formation is critical because it directly impacts the cable's performance, safety, and lifespan. The formation influences:

• Heat Dissipation: The ability of the cable to dissipate heat generated by the current.

• Electromagnetic Fields: The strength and balance of the magnetic fields created by the cables.

• Induced Voltage and Current: The amount of circulating current and induced voltage in the cable's metallic sheath, which can cause significant losses.

The correct formation, combined with our high-quality underground cable laying equipment, ensures optimal performance and reliability for the entire cable system.

A successful 132kV cable installation requires a full suite of high-quality tools and equipment. Key items include:

• Cable Drum Handling Equipment: Heavy-duty cable jacks and drum trailers are essential for safely transporting and unwinding large, heavy cable drums.

• Cable Laying Equipment: Cable winches with controlled pulling force are crucial to prevent over-tensioning and damage to the cable. Cable rollers are used to support the cable and reduce friction during pulling.

• Duct and Trenching Tools: Duct rods and duct brushes ensure a clear path for the cable, while trench shoring systems provide safety for the ground crew during excavation.

• Cable Accessories: Cable pulling socks and swivel links are vital for connecting the cable to the pulling rope and preventing twisting.

Answer: The trefoil formation is created by laying three single-core cables in a triangular configuration, held together by specialized cable cleats. This formation is commonly used for Medium Voltage (MV) and High Voltage (HV) applications.

The main advantages of the trefoil formation are:

• Reduced Induced Currents: The close proximity of the three phases balances the magnetic fields, significantly reducing induced currents and losses in the cable sheaths.

• Minimal Electromagnetic Interference: This balanced formation minimizes external magnetic fields, making it the preferred choice when laying cables near sensitive control or communication lines.

• Compact Installation: It requires less trench width compared to a flat formation, which can be advantageous in constrained or congested areas.

High-voltage cable projects present significant challenges that require careful planning and execution. The main challenges are:

• Heavy and Bulky Equipment: The size and weight of 132kV cables and accessories demand robust and reliable equipment to prevent accidents.

• Complex Logistics: Route planning, managing traffic, and working in crowded urban environments require precise coordination.

• Technical Precision: Proper cable bending radius, pulling tension, and jointing procedures are critical to the long-term reliability of the cable. Any deviation can lead to system failure.

• Safety: The primary safety risks include electrical hazards, excavation collapses, and accidents from handling heavy machinery. Proper training, risk assessments, and the use of high-quality, certified safety equipment are paramount.

Professional Answer: The term "cable laying factor" refers to the various environmental and installation conditions that influence a power cable's ability to dissipate heat. These factors are critical because they directly determine the cable's ampacity, or maximum current-carrying capacity. During electrical construction, the heat generated by current flow (I²R losses) must be effectively dissipated into the surrounding environment. If heat dissipation is restricted, the cable's temperature will rise, potentially damaging the insulation, shortening its lifespan, and causing system failures. Therefore, correctly assessing and applying these derating factors is essential for ensuring the safety, reliability, and longevity of any power line installation. Ningbo Changshi provides specialized equipment to help technicians manage these factors and achieve optimal installation conditions.

Answer: A flat formation involves laying three single-core cables side-by-side in a trench. It is often used for Low Voltage (LV) and Medium Voltage (MV) applications where balancing electromagnetic fields is less of a concern.

Key reasons to choose a flat formation include:

• Better Heat Dissipation: Because the cables are spaced further apart, the flat formation allows for better heat dissipation from each cable into the surrounding soil. This can increase the current-carrying capacity (ampacity) of the cables.

• Easier Installation: In some cases, a flat formation can be simpler to install without the need for specialized trefoil cleats, especially when the cables are smaller.

At Ningbo Changshi, we provide a comprehensive one-stop supply and service for both overhead and underground power line projects. Our products are specifically designed to meet the rigorous demands of EHV applications like 132kV cable laying. We offer a full range of equipment, from hydraulic pullers and tensioners to specialized cable rollers and drum handling systems. Our expertise and high-quality tools help our clients execute projects with maximum safety, efficiency, and precision, ensuring the integrity and longevity of the power network.

Professional Answer: Soil thermal resistivity is one of the most critical factors for underground cable installations. It measures the soil's ability to resist the flow of heat. A high thermal resistivity means the soil is a poor conductor of heat, trapping the heat generated by the cable and causing its temperature to rise. This requires the cable's ampacity to be "derated," or lowered, to prevent overheating. Conversely, soil with low thermal resistivity (e.g., wet clay) allows for better heat dissipation, permitting a higher current load. Our company offers a range of tools and equipment to prepare trenches and manage backfill materials, ensuring optimal thermal environments for your buried cables.

Answer: At Ningbo Changshi, we understand that selecting the correct installation method is critical for the longevity and reliability of the power system. The primary methods for laying 11kV underground cables include:

• Direct Laying: This is the most common and cost-effective method. It involves burying the cable directly in a trench. A fine sand bed is used to protect the cable from moisture and mechanical damage, followed by a layer of protective bricks or tiles.

• Draw-in System: Cables are pulled through pre-installed ducts or conduits, typically made of concrete or steel. This method is preferred in urban areas with high congestion of other utilities and allows for easier replacement or maintenance in the future.

• Trough Laying: Cables are laid in pre-cast concrete or fiberglass troughs, which are then covered. This method offers excellent protection and is often used in substations or industrial environments.

Professional Answer: When multiple cables are grouped together in a single conduit, trench, or cable tray, they generate mutual heating. This leads to a cumulative temperature rise that restricts the heat dissipation of each individual cable. As a result, the ampacity of each cable must be derated to compensate for the reduced cooling efficiency. The derating factor applied depends on the number of cables, their spacing, and the overall installation method. We supply a variety of cable laying and stringing equipment designed to ensure proper spacing and arrangement, minimizing derating requirements and maximizing system efficiency.

Answer: The installation of 11kV cables requires meticulous planning and strict adherence to safety protocols to mitigate risks. Key challenges include:

• Cable Integrity: Preventing mechanical damage during transportation, handling, and pulling is paramount. Using specialized cable handling and pulling equipment is crucial to avoid bending, twisting, or sheath damage.

• Excavation and Civil Works: Trenching must be carefully managed to avoid existing underground utilities like water, gas, or telecommunication lines. Advanced techniques like vacuum excavation can be employed to navigate complex routes safely.

• Environmental Factors: Unstable ground conditions, adverse weather, and site-specific challenges require careful planning and site-specific solutions.

• Personnel Safety: Working with high-voltage cables demands comprehensive safety training, proper personal protective equipment (PPE), and clear risk assessments to protect workers from electrical hazards.