Group-2-report.pdf

Group 2: Baladad, Trisha Kieth E. Cayas, Mark Angelo C. Mabulac, Ian Joshua D  Topics to be discuss 1. Typical Underground 2. Conductor Size 3. Conductor Materials 4. Underground Cable Cable Configuration Designations and Configuration Insulation Mate...

Group 2: Baladad, Trisha Kieth E. Cayas, Mark Angelo C. Mabulac, Ian Joshua D  Topics to be discuss 1. Typical Underground 2. Conductor Size 3. Conductor Materials 4. Underground Cable Cable Configuration Designations and Configuration Insulation Materials 5. Insulation 6. Conductor 7. International Cable Fabrication Shields and Specifications Insulation Shields UNDERGROUND CONFIGURATION  Features: SINGLE-CORE Conductors: Copper/aluminum unless stated CABLES Insulation: Often made of cross- linked polyethylene (XLPE) or Each phase of the electrical ethylene propylene rubber (EPR). system is carried by a separate single-core cable. Shielding: Metallic shields or Commonly used for high- screens to protect against voltage (HV) transmission lines (typically above 33 kV). electrical interference and improve safety. Armor: Steel wire or tape armor to provide mechanical protection.  Features: THREE-CORE Conductors: Copper or aluminum. CABLES Insulation: XLPE or EPR. Screening: Individual phase All three phases of the screening or a combined screen. electrical system are contained within a single Armor: Generally steel wire armor cable. (SWA) for mechanical protection. Typically used for medium- voltage (MV) distribution networks (1 kV to 33 kV) and some low-voltage (LV) applications (up to 1 kV).  Features: Conductors: Copper/aluminum FLAT OR TRIPLEX unless stated CABLE ASSEMBLIES Insulation: Often made of cross- linked polyethylene (XLPE) or ethylene propylene rubber (EPR). Each phase of the electrical system is carried by a Shielding: Metallic shields or separate single-core cable. screens to protect against Commonly used for high- electrical interference and voltage (HV) transmission improve safety. lines (typically above 33 kV). Armor: Steel wire or tape armor to provide mechanical protection.  Conductor Size Designations Metric Sizes (International Electrotechnical Commission Standard, European and International) Conductors are sized by their Typical sizes include: cross-sectional area in square Small Sizes: 1.5 mm², 2.5 mm², 4 mm², 6 mm², 10 millimeters (mm²). mm² Medium Sizes: 16 mm², 25 mm², 35 mm², 50 mm² Large Sizes: 70 mm², 95 mm², 120 mm², 150 mm², 185 mm² Extra Large Sizes: 240 mm², 300 mm², 400 mm², 500 mm², 630 mm², 800 mm², 1000 mm²  American Wire Gauge (AWG) (North American Standard) Used primarily in North America Typical sizes include: for smaller conductor sizes Small Sizes: 18 AWG, 16 AWG, 14 AWG, 12 AWG, 10 (typically below 1,000 kcmil). AWG, 8 AWG, 6 AWG Sizes decrease numerically as the conductor cross-sectional Medium Sizes: 4 AWG, 3 AWG, 2 AWG, 1 AWG area increases. Larger Sizes: 1/0 AWG (0 AWG), 2/0 AWG, 3/0 AWG, 4/0 AWG Circular Mils (kcmil or MCM) (North American Standard) Used for larger conductor sizes Typical sizes include: (typically above 1 AWG or 4/0 Large Sizes: 250 kcmil, 300 kcmil, 350 kcmil, 400 AWG). kcmil, 500 kcmil, 600 kcmil, 750 kcmil, 1000 kcmil, kcmil stands for "thousands of 1250 kcmil, 1500 kcmil, 2000 kcmil circular mils," a unit of area used to describe the cross- sectional area of round conductors. CONDUCTOR MATERIAL AND CONFIGURATION What are Conductors? Conductors are materials that facilitate the flow of electrical current. They play a crucial role in the operation of electrical systems by providing a pathway for the movement of electrons. Characteristics of Conductors: High Electrical Conductivity: Allows free movement of electrons, enabling efficient energy transmission. Low Resistivity: Minimizes resistance, reducing energy loss as heat.  Common Conductor Materials Copper (Cu): Aluminum (Al): Higher conductivity, better Lighter weight and lower cost flexibility, and resistance to compared to copper but requires a corrosion. Often used in situations larger cross-sectional area to where superior electrical achieve the same current-carrying performance is required. capacity due to lower conductivity. Advantages: Lightweight, cost- Advantages: High conductivity, effective, good conductivity. ductility, and durability. Disadvantages: Lower conductivity Disadvantages: Heavier and compared to copper, prone to more expensive than aluminum. oxidation. Factors Affecting Conductor Size Selection Current-Carrying Capacity (Ampacity): The conductor size must support the expected load current without excessive heating. Voltage Drop: Larger conductors reduce voltage drop over long distances, which is important to maintain efficiency in power distribution. Short-Circuit Current Rating: The conductor size must withstand thermal and mechanical stresses during fault conditions. Installation Environment: Factors like soil thermal resistivity, ambient temperature, and cable installation depth affect the cable's thermal management and ampacity. Regulatory Standards: Compliance with local and international standards, such as the National Electrical Code (NEC) in the U.S. or the International Electrotechnical Commission (IEC) standards globally, is essential for safety and reliability. CONDUCTOR CONFIGURATIONS 1. Solid Conductor A single, solid piece of metal, typically used for small conductor sizes. Advantages: Disadvantages: Uses: Simple construction Less flexible compared Common in low-voltage with high mechanical to stranded applications where cable strength. conductors, making flexibility is not a primary Less susceptible to installation in tight or concern, such as corrosion due to the curved spaces more residential wiring. absence of gaps. challenging. 2. Stranded Conductor Made of multiple smaller gauge wires twisted together to form a single conductor. Stranded conductors can have varying numbers of strands depending on flexibility requirements. Advantages: Disadvantages: Uses: More flexible than solid Slightly higher resistance Widely used in both low- conductors, making them than a solid conductor of voltage and medium- easier to install in bends and the same cross- voltage underground confined spaces. sectional area due to air cables, particularly where Better resistance to vibration gaps between strands. flexibility and ease of and flexing, which reduces installation are important. the risk of breakage. 3. Compressed and Compact Conductors Compressed: Stranded conductors that are compressed to reduce the overall diameter of the cable while maintaining the same current- carrying capacity. Compact: Stranded conductors where the individual strands are shaped (often trapezoidal) to fit closely together, reducing the overall diameter even more than compressed conductors. Advantages: Uses: Reduced cable diameter allows Commonly used in medium- for easier installation in ducts or voltage (MV) and high-voltage conduits. (HV) cables, where Improved electrical performance compactness and reduced by minimizing air gaps and installation space are desirable. optimizing the conductor's shape. 4. Segmental Conductor A conductor split into several segments (usually three or four) insulated from each other but bundled together. The segments are designed to reduce the skin effect and eddy current losses in AC applications. Advantages: Uses: Reduces AC resistance and losses Used in high-voltage (HV) and in high-current applications. extra-high-voltage (EHV) Improves overall efficiency for underground cables for long- large cross-sectional area distance transmission and conductors. high-current applications.  Considerations for Material and Configuration Selection Electrical Requirements: The conductor material and size must meet the electrical load's current-carrying capacity and voltage level. Corrosion Resistance: For environments with high moisture or chemical exposure, corrosion resistance is crucial. Copper is inherently resistant, while Mechanical Requirements: aluminum requires additional coatings or The installation environment, such as insulation. bending radius, pulling tension, and mechanical stresses, influences the choice of conductor material and configuration. Cost and Weight: Aluminum conductors are more cost- Thermal Considerations: effective and lighter than copper, making The conductor must dissipate heat them suitable for large-scale installations efficiently to prevent overheating, especially where cost and weight are significant in densely packed underground installations. factors. UNDERGROUND CABLE INSULATION MATERIALS  High Electrical PROPERTIES Insulation: Excellent dielectric properties, making CROSS-LINKED POLYETHYLENE (XLPE) it suitable for various voltage Thermal levels. Stability: XLPE is a thermosetting polymer that Can withstand higher becomes cross-linked through a operating chemical or physical process, temperatures (typically up to 90°C for improving its thermal and continuous operation Mechanical mechanical properties. Strength: and up to 250°C for short-circuit conditions). Resistant to abrasion, cutting, and impact, providing robust protection against Chemical Resistance: mechanical damage. Highly resistant to moisture, chemicals, and oils. USES Widely used in LV, MV, and HV underground cables due to its excellent overall performance and durability. ADVANTAGES Low dielectric Enhanced Improved resistance to loss, improving thermal aging electrical stress and energy characteristics, partial discharge, efficiency. leading to a making it suitable for longer lifespan. medium-voltage (MV) and high-voltage (HV) applications.  Good Electrical PROPERTIES Insulation: Provides adequate electrical insulating POLYVINYL CHLORIDE (PVC) properties for low and medium Flexibility: voltage PVC is a thermoplastic polymer applications. Can be made flexible or commonly used as an insulation rigid, depending on material for various electrical additives and formulations. applications. Chemical Resistance: Resistant to chemicals, oils, and acids. Flame Retardant: Inherently flame retardant, providing additional safety in fire-prone environments. USES Commonly used in LV underground cables and wiring applications, particularly where cost and flexibility are priorities. ADVANTAGES Cost-effective Suitable for a Easy to process and and widely range of manufacture. available. environments due to its good all-around performance. DISADVANTAGES Releases toxic fumes Lower thermal stability when burned, which can compared to XLPE be hazardous in (typically up to 70°C for confined spaces. continuous operation).  Excellent Electrical PROPERTIES Properties: ETHYLENE PROPYLENE RUBBER (EPR) Good dielectric strength and low High dielectric losses. Thermal EPR is an elastomeric material used Stability: for insulation in medium and high- Suitable for higher operating voltage cables. temperatures (typically up to 90°C for Flexibility and continuous operation Resilience: and up to 250°C for short-circuit Highly flexible, conditions). maintaining flexibility over a wide range of temperatures. Moisture Resistance: Good resistance to moisture and water ingress. USES Often used in MV and HV cables where flexibility and resistance to thermal and environmental stress are required. ADVANTAGES Superior resistance to Maintains flexibility at low heat, ozone, and temperatures, making it weathering, making it easier to handle and suitable for harsh install. environments.  PROPERTIES Low Smoke Emission: LOW SMOKE ZERO HALOGEN (LSZH OR LSOH) Produces minimal smoke LSZH materials are thermoplastic or in the event of a fire, reducing visibility issues thermosetting compounds designed and aiding in evacuation. Halogen- Free: to emit low smoke and no halogens when exposed to fire. Does not release toxic halogen gases (such as chlorine) when burned, improving Good safety. Electrical Insulation: Provides adequate insulating properties for low and medium voltage applications.  USES Used in LV and MV cables, particularly where fire safety and reduced toxicity are critical considerations. ADVANTAGES DISADVANTAGES Enhanced safety Increasingly Generally more in enclosed or required by safety expensive than PVC and poorly ventilated regulations in may have different environments, public buildings mechanical properties. such as tunnels, and critical subways, and infrastructure. high-rise buildings.  PROPERTIES Good Electrical Insulation: PAPER-INSULATED LEAD-COVERED (PILC) The impregnated PILC cables use layers of paper provides excellent insulating impregnated paper as the insulating properties. Thermal Stability: material, encased in a lead sheath for moisture protection. Can handle moderate operating temperatures. Moisture Resistance: The lead sheath provides excellent protection against moisture ingress. USES Used in older underground cable systems, particularly in HV applications. PILC cables are gradually being phased out in favor of more modern materials like XLPE. ADVANTAGES Historically used Suitable for HV for high- applications reliability where longevity installations due and reliability to excellent are critical. moisture resistance. DISADVANTAGES Bulky and heavy, Lead sheath can Less flexible than making be modern insulation installation more environmentally materials. labor-intensive. hazardous and requires special handling.  PROPERTIES Excellent Heat Resistance: SILICONE RUBBER Can operate at very A flexible, thermosetting elastomer high temperatures (typically up to with high temperature and fire- 180°C). Good Electrical resistant properties. Insulation: Maintains insulating properties across a wide temperature range. Flexibility: Remains flexible at low temperatures and resists thermal aging. USES Primarily used in specialized applications where high flexibility and temperature resistance are required, such as in fire- resistant cables or high-temperature environments. ADVANTAGES Ideal for applications Good resistance to where high weathering, UV radiation, temperatures or fire and ozone. resistance are critical. INSULATION FABRICATION Step 1. Material Preparation Raw Material Selection: The appropriate base materials for the insulation, such as polyethylene for XLPE or polyvinyl chloride (PVC) for PVC insulation, are selected based on the desired properties. Additives and Fillers: Additives, such as stabilizers, antioxidants, flame retardants, and UV inhibitors, may be mixed with the base material to enhance the insulation's performance characteristics. Fillers like talc, calcium carbonate, or silica may also be added to modify mechanical properties or reduce costs. Step 2.Compounding Mixing: The base polymer, additives, and fillers are mixed together in specific proportions to create a homogenous compound. This is often done using high-shear mixers or extruders to ensure even distribution of all components. Melt Compounding: For thermoplastic insulation materials (e.g., PVC), the mixture is heated and melted to achieve a uniform consistency. For thermosetting materials (e.g., XLPE), the mixture is prepared without initiating the cross-linking reaction. Step 3. Extrusion Application of Insulation: Primary Extrusion: The melted compound is extruded around the conductor, forming a uniform layer of insulation. The thickness of the insulation layer is controlled by the die size and extrusion speed. Screening or Shielding (if required): For cables that require additional layers for electrical shielding (such as medium- and high-voltage cables), a conductive or semi-conductive layer may be extruded over the primary insulation. Step 4. Cross-Linking (for XLPE and EPR Insulation) Heating Process: For cross-linked materials like XLPE or EPR, the insulated conductor passes through a high-temperature curing or vulcanization process. This can be done using various methods, such as steam curing in a catenary line, a continuous vulcanization (CV) tube, or a nitrogen gas environment to avoid oxidation. Cross-Linking Reaction: The heat triggers a chemical reaction in the insulation material, causing the polymer chains to form cross-links. This process converts the thermoplastic into a thermoset material, which enhances its thermal and mechanical properties. Cooling and Quenching: After the cross-linking process, the cable is cooled quickly using water or air to solidify the insulation and stabilize the dimensions of the cable. Step 5. Quality Control and Testing Dimensional Checks: The insulation thickness and uniformity are checked using precise measuring instruments to ensure compliance with design specifications. Electrical Testing: The insulated cable undergoes electrical tests to verify its insulating properties, including dielectric strength tests, insulation resistance tests, and partial discharge tests for high-voltage applications. Mechanical Testing: The insulation is subjected to mechanical tests to assess its tensile strength, elongation, impact resistance, and flexibility. For cables that need to withstand specific environmental conditions, additional tests for abrasion resistance, crush resistance, and moisture ingress may be performed. Thermal Testing: Thermal tests, including heat aging and thermal endurance tests, are conducted to ensure that the insulation material can withstand the operating temperatures and thermal cycling without degradation. Step 6. Final Quality Control and Packaging Final Inspection: The finished cable undergoes a final round of quality control checks, including visual inspection, electrical testing, and dimensional verification, to ensure it meets all specifications and standards. Coiling and Packaging: The cable is coiled onto drums or reels, labeled, and packaged for transport. Protective coverings and markings are applied to identify the cable type, size, voltage rating, and manufacturing details. CONDUCTOR SHIELDS AND INSULATION SHIELDS 1.Conductor Shield Functions: The conductor shield, also known as the conductor screen or conductor Smooth Electric Field: The conductor shield ensures that the electric field within semiconductor, is a semi-conductive layer the insulation is uniform, preventing localized high-stress applied directly over the conductor. Its points that could lead to insulation failure. primary purpose is to provide a smooth Surface Irregularity Mitigation: interface between the conductor and the It fills in any surface irregularities or voids around the conductor, ensuring a smooth transition between the insulation, reducing electrical stress conductor and the insulation. concentrations. Stress Relief: By eliminating sharp points and unevenness on the conductor surface, the shield reduces electrical stress at the conductor-insulation interface, minimizing the risk of partial discharges, which can damage the insulation over time. Material: Application: Semi-Conductive Compounds: Typically Extruded Layer: The conductor shield is made from a semi-conductive material, such usually extruded directly onto the as a carbon black-filled polyethylene or conductor during the cable manufacturing ethylene-propylene rubber (EPR) compound. process. This extrusion ensures uniform These materials have a controlled electrical thickness and intimate contact with the conductivity that allows them to conduct a conductor, which is essential for effective small amount of electrical current without stress management. fully insulating or fully conducting, providing a gradual transition of the electric field. 2.Insulation Shield Functions: The insulation shield, also known as the Electric Field Control: insulation screen or insulation Like the conductor shield, the insulation shield helps semiconductor, is a semi-conductive layer control the electric field within the cable, ensuring it remains within the insulation and does not reach the outer applied over the insulation layer. It serves layers of the cable. to confine the electric field within the Mechanical Protection: insulation and provide a smooth interface The insulation shield protects the insulation from mechanical damage caused by any metallic shield, armor, between the insulation and any metallic or other external layers applied over it. shield or armor. Improved Grounding: It provides a uniform grounding layer, ensuring the outer surface of the insulation is at a uniform potential, which helps in reducing electrical interference and prevents unwanted current flow through the insulation. Material: Application: Semi-Conductive Compounds: Made from Extruded Layer: The insulation shield is similar semi-conductive materials as the also extruded over the insulation layer conductor shield, like carbon black-filled during the manufacturing process, polyethylene or EPR. These materials must ensuring it adheres tightly and uniformly be smooth and free of impurities to avoid to the insulation. It is typically applied in a creating points of high electrical stress. triple extrusion process alongside the conductor shield and the insulation. 1. Metallic Shield (Screen or Armor) Functions: for Cable Protection Electromagnetic Shielding: While the conductor and insulation shields Protects the cable from external electromagnetic are semi-conductive and directly related interference (EMI) and prevents the cable itself from emitting electromagnetic fields that could interfere with to managing electrical stress, a metallic nearby equipment. shield or armor may also be applied over Ground Path: the insulation shield, particularly in MV Provides a path for fault currents and helps in the safe grounding of the cable, reducing the risk of electrical and HV cables. shock or fire in case of insulation failure. Mechanical Protection: In armored cables, the metallic layer (often made of steel tape or wires) provides additional mechanical protection against physical damage, impacts, and external forces. Material: Metallic Tapes or Wires: Often made from copper or aluminum tapes for grounding purposes. In some cases, steel wire armor is used for mechanical protection, especially in harsh environments or when additional strength is needed.  Summary of Conductor and Insulation Shields Note: Component Purpose Material Application Conductor and insulation shields are essential Smooth electric field, Semi-conductive Extruded directly over components of underground Conductor Shield reduce stress compounds (carbon the conductor concentrations black-filled PE or EPR) cables, especially in MV and HV applications. They ensure Control electric field, Semi-conductive the cable operates safely and Insulation Shield mechanical compounds (carbon Extruded over the insulation reliably by managing electrical protection, grounding black-filled PE or EPR) stresses, providing mechanical protection, and enhancing Electromagnetic Metallic tapes overall cable performance. Metallic Shield shielding, grounding, (copper/aluminum) or Applied over the mechanical insulation shield steel wires protection INTERNATIONAL CABLE SPECIFICATION International cable specifications ensure that underground cables meet certain standards for safety, reliability, and performance across different applications and environments. These specifications cover various aspects, including construction, materials, electrical properties, and testing methods. Different international standards organizations have developed specifications for underground cables, such as the International Electrotechnical Commission (IEC), the Institute of Electrical and Electronics Engineers (IEEE), and others.  Here's a table summarizing some key international cable specifications for underground cables: Standard Standard Organizatio Title Key Specifications Typical Applications Number n Defines classes of conductors (Class 1: Solid, Class 2: Stranded, Class All types of power IEC IEC 60228 Conductors of Insulated Cables 5: Flexible, etc.), material properties, sizes, and resistance. cables Power Cables with Extruded Insulation Low Voltage (LV) and and Their Accessories for Rated Specifies construction, materials, test requirements, and dimensions for IEC IEC 60502-1 Medium Voltage (MV) Voltages from 1 kV (Um = 1.2 kV) up to cables with extruded insulation for LV and MV applications. cables 30 kV (Um = 36 kV) Power Cables with Extruded Insulation Covers construction, testing, and requirements for high-voltage power and Their Accessories for Rated High Voltage (HV) IEC IEC 60840 cables with extruded insulation, typically XLPE or EPR, and their Voltages above 30 kV (Um = 36 kV) up cables accessories. to 150 kV (Um = 170 kV) Power Cables with Extruded Insulation Provides specifications for extra-high voltage (EHV) cables with extruded Extra High Voltage IEC IEC 62067 and Their Accessories for Rated insulation, including design, materials, and testing protocols. (EHV) cables Voltages above 150 kV (Um = 170 kV)  Here's a table summarizing some key international cable specifications for underground cables: Standard Standard Title Key Specifications Typical Applications Organization Number Separable Insulated Connector Specifies requirements for connectors and separable insulated Underground IEC IEEE 386 Systems for Power Distribution connectors used in underground distribution systems, focusing on safety distribution systems Systems Rated 2.5 kV through 35 kV and reliability. Provides guidelines for field testing shielded power cable systems rated 5 Guide for Testing Shielded Power MV and HV shielded IEC IEEE 402 kV and above, including high-potential testing, insulation resistance Cable Systems cables testing, and partial discharge testing. NEMA WC Power Cables Rated 2000 Volts or Specifies requirements for Low Voltage (LV) NEMA 70/ICEA S- Less for the Distribution of Electrical construction, materials, and performance for LV power cables, including cables 95-658 Energy thermoplastic and thermoset insulated cables. NEMA WC Standard for Non shielded Power Outlines specifications for Medium Voltage NEMA 71/ICEA S- Cables Rated 2001-5000 Volts for Use non-shielded MV cables, including insulation types, thickness, and (MV) cables 96-659 in the Distribution of Electrical Energy performance criteria.  Here's a table summarizing some key international cable specifications for underground cables: Standard Standard Title Key Specifications Typical Applications Organization Number Distribution Cables with Extruded Insulation for Rated Voltages from Covers the design, testing, and Medium Voltage CENELEC HD 620 S2 3.6/6 kV (Um = 7.2 kV) to 20.8/36 kV performance of MV distribution cables with extruded insulation used in (MV) cables in Europe (Um = Europe, including materials and mechanical properties. 42 kV) Specification for Power Cables with Extruded Insulation and Their Defines the construction and Medium Voltage BSI BS 6622 Accessories for Rated Voltages from performance standards for MV power cables in the UK, focusing on (MV) cables in the UK 3.8/6.6 kV XLPE-insulated cables and their accessories. up to 19/33 kV LV and MV Polymeric Insulated Provides detailed specifications for LV and MV cables Cables LV and MV polymeric insulated cables, including XLPE, EPR, and PVC BSI BS 7870 for utilities in the for Use by Distribution and Generation insulation UK Utilities materials.  Key Points to Note: IEC (International IEEE (Institute of NEMA CENELEC (European Electrotechnical Electrical and (National Electrical Committee for Electronics Engineers) Manufacturers Electrotechnical Commission) Association) and ICEA Standardization) and BSI (Insulated Cable (British Standards standards are widely standards are Institution) primarily used in Engineers Association) recognized and used globally. They cover North America but standards are also have a global standards provide primarily used in various aspects of guidelines for cable influence, especially Europe and the UK, cable design, design and testing respectively, and are in the testing and construction, in North America, tailored to the performance materials, and focusing on specific requirements evaluation of cable testing. performance and of those regions. systems. safety. 1.Which type of cable is typically used for high-voltage transmission lines? A. Three-core cables B. Single-core cables C. Triplex cable assemblies D. Compressed conductors 2. Which insulation material is commonly used in both low-voltage and medium-voltage applications? A. XLPE (Cross-linked Polyethylene) B. PVC (Polyvinyl Chloride) C. EPR (Ethylene Propylene Rubber) D. LSZH (Low Smoke Zero Halogen) 3. What is the main advantage of aluminum conductors compared to copper conductors? A. Higher conductivity B. Lower weight and cost C. Higher flexibility D. Better resistance to oxidation 4. Which conductor configuration is most commonly used in high-current applications to reduce skin effect losses? A. Solid conductor B. Stranded conductor C. Segmental conductor D. Compressed conductor What is the primary function of a conductor shield in underground cables? 5. What is the primary function of a conductor shield in underground cables? A. To provide mechanical protection B. To reduce electrical stress concentrations C. To improve flexibility D. To increase current-carrying capacity 6. Which standard organization defines the classes of conductors (e.g., solid, stranded, flexible)? A. IEEE B. IEC C. NEMA D. CENELEC 7. What is the key disadvantage of PVC as an insulation material compared to XLPE? A. Lower flexibility B. Releases toxic fumes when burned C. Higher cost D. Poor resistance to moisture 8. What type of armor is typically used in medium-voltage cables for mechanical protection? A. Aluminum tape armor B. Steel wire armor C. Copper wire shield D. Paper-insulated lead covering 9. Which insulation material is known for superior flexibility and resilience over a wide range of temperatures? A. PVC B. XLPE C. EPR D. PILC (Paper-Insulated Lead Covering) 10. What is a key advantage of using XLPE insulation in underground cables? A. Low cost and availability B. High resistance to fire C. Excellent thermal stability and high operating temperature D. Enhanced flexibility in cold environments