In a power transmission and distribution network, cables and conductors are among the most critical components. They form the backbone of the power sector. Any failure within this network can disrupt power evacuation and affect end-user power delivery. Therefore, timely, comprehensive and accurate testing of cables and conductors is essential to ensure a stable and reliable power supply. With the growing electricity demand, it becomes even more important to maintain these components in optimal condition through effective testing and measurement (T&M) techniques.
Cables and conductors are not only vital for expanding new transmission networks but also for strengthening existing grids, particularly in areas where space constraints limit the laying of new lines. This situation underscores the need for a robust network supported by adequate T&M practices. The testing and monitoring of power equipment play a crucial role in maintaining operational efficiency and ensuring round-the-clock electricity supply across the country. To achieve optimal performance and prevent equipment failures, utilities must adopt well-defined T&M practices for cables and conductors.
Key developments
In March 2024, the Central Electricity Authority (CEA) has issued an advisory, urging power sector companies to rigorously adhere to quality control orders and established standards for materials such as aluminium ingots, wire rods and wires, crucial for manufacturing conductors and cables. These include compliance with standards such as IS 5484 and IS 2067 for aluminium rods and wires, and IS 4026 for aluminium ingots. The CEA’s guidelines call for conductor and cable manufacturers to implement mandatory processes and quality checks. These standards apply to all tenders issued by transmission and distribution companies nationwide. The Bureau of Indian Standards, along with the mines ministry and the Department for Promotion of Industry and Internal Trade, had issued these quality control orders for aluminium and aluminium alloy products. The move aligns with the government’s aim to enhance product quality in the power sector, promote Indian manufacturing, encourage “Made in India” products and achieve self-reliance. To ensure compliance, the CEA has mandated that suppliers of these raw materials provide quality test certificates before bidding for conductor and cable supply contracts. Additionally, the CEA requires that sampling and inspection of conductors and cables be carried out at the delivery site specified in the contract. This process is to be conducted in addition to the existing inspections and testing at the manufacturer’s or supplier’s facilities.
The CEA also recommends the adoption of high-performance conductors (HPCs) made from diverse materials, including galvanised steel, zinc alloy and fibre-reinforced composites. While India lacks adequate test facilities for HPCs, leading to reliance on international testing centres and increased costs, these conductors provide cost efficiencies over time. Despite being two to three times more expensive than conventional conductors, HPCs reduce losses and associated operational expenses, making them an economically viable choice in the long term.
Additionally, in May 2024, the CEA released guidelines for testing the carbon fibre composite (CFC) core of high-temperature low-sag conductors. The advisory emphasises including a mandatory “galvanic protection barrier layer thickness test” in power sector procurement tenders, aligned with the ASTM B987 standards. It further specifies that the salt spray test is unsuitable for determining the thickness of the galvanic protection barrier layer on CFC cores, as no correlation exists between the two tests.
Emerging trends – conductor and cable testing
- Smart cables: With the increasing demand in power systems, cable testing has evolved to incorporate advanced technologies for better efficiency, accuracy and safety. One of the significant advancements in this domain is the emergence of smart cables. These cables are embedded with sensors and communication modules that enable real-time monitoring of operational parameters such as temperature, mechanical stress and voltage. This continuous data stream not only supports early fault detection but also enables adaptive power management strategies, significantly enhancing grid reliability and performance.
- Use of automation and robotics: The use of automation and robotics is also gaining traction in cable and conductor testing. Automated test systems and robotic arms are being deployed to handle repetitive and high-risk testing activities, ensuring consistency, while minimising human intervention. These systems are particularly useful in hazardous or hard-to-reach environments, reducing exposure risks and improving testing efficiency. Fibre-optic monitoring presents another cutting-edge approach to cable assessment. Fibre optics integrated within or along the cable can detect minute temperature variations and other environmental changes. This allows for precise thermal profiling and condition monitoring even when the conductor is under load, enabling utilities to prevent overheating and optimise load distribution in real time.
- Online and offline test: A combination of online and offline testing methods is used to get a comprehensive understanding of cable health. Online tests are conducted without taking the system out of service and are ideal for routine monitoring. In contrast, offline tests offer deeper diagnostics, but often require the cable to be de-energised, leading to planned outages. Together, they provide a balanced approach for predictive and preventive maintenance. Further, visual inspection techniques remain a key part of cable testing, especially for overhead lines. Ground-based inspections are being enhanced with high-resolution cameras and AI-enabled analysis, while aerial inspections using drones and helicopters are becoming more common. However, environmental factors such as glare, rain, or fog can hinder visibility, making it essential to complement these methods with other diagnostic tools.
- Non-invasive testing: Techniques such as online partial discharge (PD) testing, time-domain reflectometry and thermal infrared imaging play a crucial role in modern cable diagnostics. These methods allow utilities to assess the internal condition of cables without physically accessing them, identifying issues such as insulation degradation, water ingress, or joint failure without service interruption. By leveraging such technologies, utilities can ensure proactive maintenance and extend the life of critical cable asset. Several standard tests are widely used to assess cable integrity. PD testing is a vital diagnostic technique used to evaluate the insulation condition of critical electrical equipment. PD occurs due to localised breakdowns within the insulation, causing small discharges of electrical energy. If not addressed, these discharges can progressively damage the insulation, potentially leading to equipment failure. A key benefit of PD testing is its ability to identify insulation defects at an early stage, allowing for timely maintenance and corrective action. Continuity tests verify that electrical paths are intact and properly connected. Insulation resistance tests measure the resistance of the dielectric material to electrical flow, and earth resistance tests ensure the effectiveness of grounding systems. High-voltage tests are used to verify the dielectric strength of the insulation under elevated electrical stress.
- Test for HVDC cables: The need to test longer HVDC cables, often exceeding 200 metres due to complex routing through tunnels and ducts, is growing. This increased length poses challenges for testing equipment, particularly impulse generators. At the same time, there is a rising emphasis on transient overvoltage testing, which evaluates how cables perform under fault conditions in HVDC systems, especially those using voltage source converters. Utilities are now requesting polarity reversal and superimposed impulse tests to ensure the reliability of cable systems under such stresses. These tests are conducted in line with CIGRÉ TB 852 guidelines and require generating specific waveforms such as oscillating discharges and slow or fast-front impulse s. To carry out these advanced tests, laboratories are upgrading their set-ups with components such as rectifiers, reactors and coupling capacitors, enabling testing at voltage levels up to 525 kV. Another emerging trend is the use of full-scale cable loops—including joints and terminations—during type testing, which helps streamline the process and reduce the set-up time. Additionally, labs are enhancing test circuit designs and using simulations to address challenges such as DC offset and reduced testing efficiency.
- Galvanising tests for conductor: Test on steel wires verify the weight and uniformity of zinc coatings as per IS 4826-1979, ensuring corrosion resistance. Surface condition tests are conducted by applying tension equal to 50 per cent of the conductor’s ultimate tensile strength. The surface must remain cylindrical, with strands properly aligned and the measured diameter must meet the required specifications.
- Stress-strain or creep tests: These are used to assess long-term elongation under constant load. A 10-metre sample compressed with dead-end clamps provides critical data for predicting conductor performance over time, aiding in system design and lifecycle planning.
- Others: Key measurements include diameters of individual aluminium and steel wires and the lay ratio of each wire layer, both of which must match design specifications. The breaking load test, conducted using a tensile testing machine, checks the mechanical strength of individual wires. Maintaining the correct rate of jaw separation ensures accurate results. Wrapping tests are carried out to evaluate wire flexibility and ductility. Aluminium and galvanised steel wires are wrapped into helices, then unwrapped and rewrapped. Any signs of cracking or breakage indicate poor material quality. Galvanised wires undergo similar testing with mandrels to ensure coating integrity. Electrical resistance testing, especially for aluminium wires, is performed as per IEC 889, correcting results to 20°C for standardisation.
Conclusion
Overall, testing is carried out to assess the conformity, quality and functionality of components. Given the importance of conductors, proper testing is imperative. Regular testing and maintenance of cables and conductors are necessary, as the failure of even a single component can lead to widespread grid disruptions. A reliable testing procedure enhances the durability and performance of conductors, while preventing costly breakdowns. These tests provide accurate insights into potential issues, help assess their severity and reduce the recurrence of faults—ultimately increasing the overall uptime of the utility network. Moreover, effective T&M not only improves system reliability, but also results in cost savings, as preventive testing is more economical than post-failure repairs.
Akanksha Chandrakar
