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Did you know improper installation causes most MV Power Cable failures? Medium voltage power cables are vital in power distribution systems. Proper installation ensures safety and reliability. In this post, you’ll learn key installation steps, challenges, and best practices for MV power cables.
Choosing the best route for laying medium voltage (MV) cables is crucial. The path should minimize risks and ensure long-term reliability. Look for routes that avoid heavy traffic areas, places prone to digging or construction, and locations with high electromagnetic interference. The route should also allow easy access for future inspections or repairs. Avoid sharp bends or sudden changes in direction, as these can stress the cable and reduce its lifespan.
MV cables are sensitive to external forces. Avoid areas where heavy machinery operates or where the ground may shift frequently. Environmental hazards such as flooding, chemical spills, or extreme temperature changes can damage cables over time. For example, avoid placing cables near water bodies unless the cable is specifically designed for wet conditions. Also, steer clear of areas exposed to corrosive substances or where animals might gnaw on the cables.
Good drainage is essential to prevent water accumulation around buried cables. Water can degrade cable insulation and cause faults. The cable trench or channel must be free from debris and allow water to flow away easily. Ensure the trench bottom is smooth and lined with fine soil or sand to protect the cable from sharp objects. Maintain a clearance of at least 50mm on both sides of the cable when covering it with protective layers like concrete or bricks. This clearance prevents soil pressure from damaging the cable and allows for some movement without stress.
Tip: Always survey the cable route site for hidden hazards and plan drainage systems before installation to protect MV cables from future damage.
When laying medium voltage (MV) cables, temperature plays a crucial role. The ambient temperature should generally stay above 0°C. If the temperature drops below freezing, cables become stiff and prone to damage when bent. In such cases, preheating cables is essential. You can power them on or place them in a drying room until their surface temperature reaches 20-30°C. Once warmed, laying can proceed quickly. Avoid bending cables once they cool below 0°C to prevent cracks or insulation damage.
Physical damage during laying can cause long-term failures. Prevent cables from grazing against trench walls, pipes, or machinery. If you spot any abrasions or scrapes, stop immediately. Identify and remove the cause before continuing. Twisting cables also causes internal damage. Use anti-twisting devices at the pulling head to avoid this. For coiled cables, lay them following the coil’s natural direction. If twisting occurs, release it by turning in the opposite direction. Never hit cables with tools or objects, as this can cause hidden damage.
Proper tools make a big difference. Use pay-off racks and guide wheels designed for cable laying. These help feed the cable smoothly and reduce stress. Depending on site conditions, choose suitable laying methods like end traction, mechanical conveying, or manual-assisted guiding. These methods help control the cable’s movement and prevent damage. Ensure all equipment meets safety and technical standards to protect the cable and workers.
Each cable has limits on how much force it can handle and how tightly it can bend. Exceeding the maximum lateral pressure or traction force during pulling can damage the cable core or insulation. Similarly, bending cables below their minimum allowed radius causes internal stress and weak points. Always check the cable manufacturer’s specifications and follow them strictly. Use measuring tools to monitor bending radius during installation.
For direct burial, the cable must be buried at least 700mm deep. This depth protects cables from surface activities and environmental effects. The trench bottom should be smooth and free from sharp objects. Lay a 100mm layer of fine soil or yellow sand before placing the cable. After laying, cover the cable with another 100mm layer of soil or sand. Then, add protective layers like concrete or bricks, extending at least 50mm beyond the cable on both sides. This prevents soil pressure damage and moisture migration. In cold regions, bury cables below the permafrost layer or use protective measures to avoid frost damage. Mark the cable route on the surface for future reference.
Tip: Always monitor cable temperature and handle cables gently during laying to avoid hidden damage that can cause future failures.
Medium voltage (MV) cable terminal accessories mainly come in two types: cold-shrinkable and heat-shrinkable. Cold-shrinkable accessories are preferred despite higher costs because they offer better safety and ease of installation. These accessories include components like insulation tubes, branch gloves, and terminals that connect the cable’s conductor to other equipment or cables.
The installation process involves several precise steps to ensure a secure and reliable connection:
Strip Outer Sheath: Remove the cable’s outer protective layer carefully.
Remove Armor Layer: If the cable has steel tape armor, remove it cautiously. Check if armor is non-magnetic metal tape for single-core cables.
Strip Insulation Sleeve: Expose the insulation layer without damaging it.
Weld Copper Tape Grounding Wire: Attach a copper tape to act as a grounding shield; mark the wire core clearly.
Strip Insulation Shielding Layer: For 10kV cables, the semi-conductive shielding layer peels off easily, but for 35kV cables, it is non-peelable and requires careful handling.
Clean Insulating Surface: Ensure the surface is free of dust and moisture.
Install Semi-Conductive Tubes and Branch Gloves: These provide insulation and protection.
Strip Insulation Layer and Conductor Shielding: Prepare the conductor for terminal installation.
Install Insulating Sleeves and Terminals: Fit the insulating sleeves and crimp terminals securely.
Firm Grounding: The copper strip ground wire must be welded firmly to avoid loose connections.
Avoid Conductor Damage: Do not nick or scratch the conductor while stripping shielding layers; this can cause partial discharge faults.
Match Terminal Materials: Use copper-aluminum transition terminals for aluminum conductors, filled with conductive paste to ensure good conductivity.
Proper Crimping: Start crimping from the terminal’s end and work inward to secure the connection.
Seal Contact Surfaces: Ensure perfect sealing between cable insulation and terminals to prevent fault points.
Intermediate joints connect two cable ends and require similar care:
Measure Cable Lengths Accurately: Avoid cable ends being too short or long.
Control Stripping Lengths: Keep stripped layers consistent on both cables.
Crimping Sequence: Crimp one cable’s three wire cores first, then the other’s.
Ground Wire Contact: Copper strip ground wires must be solid and clearly marked.
Shielding Contact: Ensure copper wire shielding braids of both cables contact fully at the joint for proper grounding.
Proper grounding prevents induced voltages and circulating currents that cause cable heating and faults. At joints, all metallic shields and ground wires must connect tightly to avoid resistance buildup. This ensures system stability and reduces the risk of failures caused by overheating or electrical faults.
Tip: Always double-check grounding connections and shielding continuity at every joint and terminal to prevent hidden faults and ensure long-term cable reliability.
When medium voltage (MV) cables carry alternating current, they generate an alternating magnetic field around the conductor. This field links to the cable’s metal sheath, such as the shielding or armor layers, inducing a voltage in these metallic parts. If the cable sheath is not properly grounded, this induced voltage creates circulating currents along the sheath. These currents can cause the cable to heat up abnormally, even if the conductor itself is undamaged. Over time, this heating can degrade insulation and lead to faults.
Failing to ground MV cables correctly has serious consequences:
Excessive Heating: Induced currents raise the sheath temperature, risking insulation damage.
Short Circuits: Heat buildup can cause insulation breakdown and cable failure.
System Instability: Uneven grounding may lead to voltage imbalances and interference.
Safety Hazards: Overheated cables increase fire risk and endanger personnel.
Improper grounding is a common cause of cable faults, often mistaken for conductor problems. Proper grounding prevents these hidden dangers.
To avoid these issues, follow these grounding practices:
Solid Ground Connections: Ensure all metal sheaths and armor layers connect firmly to grounding points.
Continuous Shielding Contact: At joints and terminals, maintain full contact between shielding layers to avoid resistance.
Use Copper Tape Grounding: Weld copper tape shields securely to provide a low-resistance path for induced currents.
Multiple Grounding Points: Depending on cable length, ground the sheath at intervals to limit circulating current loops.
Proper Grounding Conductors: Use conductors sized according to standards to handle expected fault and induced currents.
These methods reduce induced voltage and circulating currents, keeping cable temperature within safe limits.
Safe grounding safeguards the entire power distribution system. It:
Enhances Reliability: Reduces cable faults and unplanned outages.
Improves Performance: Minimizes electrical noise and interference.
Protects Equipment: Prevents damage to transformers, switchgear, and other components.
Ensures Safety: Lowers risk of electrical shock and fire.
Grounding is not just a technical requirement but a critical step for stable, safe, and efficient MV cable operation.
Tip: Always verify grounding continuity and resistance after installation to ensure effective dissipation of induced currents and prevent cable overheating.
Medium voltage (MV) cables must match the system’s voltage requirements. The cable’s rated voltage should never be less than the system’s working voltage. Also, the system voltage should not exceed 1.2 times the cable’s rated voltage to avoid insulation breakdown. Temperature ratings are equally important. Typically, the cable’s maximum continuous operating temperature is 90°C. For short circuits lasting about 5 seconds, the conductor temperature must not exceed 250°C. Staying within these limits prevents insulation damage and extends cable life.
Overloading cables causes excessive heat, leading to insulation deterioration and premature failure. Ensure the load current stays within the cable’s rated capacity. Avoid long-term overloads, even if the cable can handle short bursts. Thermal overstress causes insulation cracks, partial discharges, and eventual breakdown. Use current monitoring and protective devices to prevent overload. Proper load management ensures safety and reliability.
When multiple MV cables run together in trays or tunnels, heat can build up quickly. Proper ventilation is critical to dissipate heat and maintain safe cable temperatures. Design cable trays with open sides or perforations to allow airflow. Use forced ventilation or cooling fans in tunnels with limited natural airflow. Avoid overcrowding cables; maintain spacing according to standards. Heat buildup reduces cable lifespan and increases failure risk, so good ventilation safeguards performance.
MV cable installation must follow all relevant codes and standards. Maintain minimum clearances between cables and other electrical equipment to prevent electrical faults and allow safe maintenance access. For example, clearance from grounded metal structures, other cables, and power equipment is regulated. Follow local electrical codes and manufacturer guidelines strictly. Compliance ensures safety, prevents interference, and meets legal requirements.
Tip: Regularly inspect cable trays and tunnels to confirm ventilation systems work properly and cables remain within safe temperature limits.
Poor installation can seriously harm MV cable reliability. Faults often arise not from the cable itself but from hidden errors during laying or accessory installation. These faults cause unexpected outages, costly repairs, and reduced system lifespan. For example, improper handling can cause micro-cracks in insulation, which grow over time and lead to breakdowns. Loose grounding or bad joints may cause overheating and faults. Such issues reduce confidence in the power system and increase downtime.
Common faults linked to installation mistakes include:
Insulation Damage: Scratches or nicks during stripping or pulling can create weak spots.
Improper Grounding: Loose or missing grounding connections cause induced currents and overheating.
Incorrect Bending Radius: Bending cables too tightly leads to internal conductor stress and eventual failure.
Poor Joint Installation: Misaligned or poorly crimped joints cause resistance, heat, and partial discharges.
Twisting and Abrasion: Twisting cables or rubbing against trench walls damages insulation and conductor layers.
Overloading During Laying: Excess traction force or pulling beyond limits damages cable cores.
To avoid faults, follow these best practices:
Strictly Follow Manufacturer Specs: Adhere to maximum bend radius, traction force, and temperature limits.
Use Proper Tools: Employ pay-off racks, guide wheels, and anti-twist devices during laying.
Inspect Cables Regularly: Check for abrasions, kinks, or damage before and during installation.
Ensure Proper Grounding: Weld copper tape grounding firmly and verify continuity at all joints.
Train Personnel: Skilled workers reduce errors and improve quality.
Control Environment: Avoid laying cables in unsuitable conditions such as extreme cold without preheating.
Standardize Procedures: Use checklists and supervision to maintain consistency.
Personnel must be well-trained in MV cable technology and installation methods. Training should cover:
Cable structure and materials
Handling and laying techniques
Accessory installation (terminals, joints)
Grounding methods and safety
Use of specialized equipment
Recognizing and preventing faults
Regular refresher courses help maintain skills and update workers on new standards or technologies. Experienced supervisors should oversee work to catch errors early. Investing in training reduces costly failures and enhances system reliability.
Tip: Invest in hands-on training and certification programs to ensure installation teams master MV cable handling, accessory fitting, and grounding techniques, minimizing costly faults.
Proper MV power cable installation requires careful route selection, temperature control, and precise accessory fitting. Following technical standards and using specialized tools ensures cable longevity and safety. Professional training and strict adherence to guidelines prevent common faults and system failures. Future maintenance depends on solid grounding and ventilation practices to sustain performance. Hangzhou Kesheng Packaging Material Co., Ltd. offers products designed to enhance cable protection and installation quality, providing reliable solutions that add value and support long-term system stability.
A: An MV Power Cable is a medium voltage cable designed for power distribution in industrial and utility networks. It transmits electricity safely between 1kV and 35kV systems.
A: Choose routes avoiding heavy traffic, digging, and electromagnetic interference, ensuring easy access and proper drainage to protect the MV Power Cable.
A: Proper grounding prevents induced voltages and circulating currents that cause overheating and faults in MV Power Cables, ensuring system stability and safety.
A: Follow manufacturer specs, use proper tools, inspect cables, ensure firm grounding, and train personnel to reduce damage and faults during MV Power Cable installation.
A: Costs depend on cable length, route complexity, protective measures, accessories like joints and terminals, and labor skill for proper MV Power Cable installation.
