Cables and conductors form the backbone of power transmission and distribution network. Their reliability and safety are paramount, necessitating rigorous testing to ensure optimal performance, durability and adherence to safety standards. The precise testing of cables and conductors is crucial for maintaining a stable power supply and meeting the rising power demand. Effective testing and measurement (T&M) practices are essential for developing new networks and strengthening existing grids, ensuring efficient operation and continuous power supply.
Testing methods for cables and conductors assess critical parameters such as resistance, voltage and impedance to ensure quality and performance. Insulation resistance tests identify potential electrical leakage, while dielectric strength tests ensure cables can handle high voltage. Continuity tests check for breaks or open circuits, and capacitance tests prevent signal distortion by evaluating charge storage. Impedance and attenuation tests assess signal integrity, which is essential for high-frequency applications.
Underground cables are commonly tested using the tan delta method to assess insulation quality and analyse long-term ageing. This test measures phase shifts caused by impurities or stress in the insulation, indicating potential temperature breakdown risks. Accurate testing of key insulation parameters is essential to gauge deterioration. Adverse installation conditions can damage cables, making health diagnostics crucial.
Overhead power lines are inspected periodically through on-ground and helicopter-aided visual inspections. However, factors such as sun glare, cloud cover and proximity to power lines make airborne inspections hazardous. Unlike underground cables, overhead lines are more accessible and can be tested with online methods. Punctured insulator detectors, which move along live wires and send readings to graphic displays, monitor insulation punctures by detecting electrical leaks. Other methods include distributed temperature sensing and sheath current monitoring.
Routine tests are regular checks to maintain consistent quality and performance of electrical cables. Type tests, commonly used as routine testing techniques, encompasses various methodologies such as partial discharge tests, tan delta measurement, conductor resistance tests, tensile tests, hot deformation tests, hot set tests, shrinkage tests and thermal stability tests. A visual examination is crucial, involving a physical inspection of the conductor under the supervision of an inspecting officer during the rewinding of the conductor drums. Apart from this, acceptance tests verify that a batch of cables meets the required specifications through mechanical and electrical tests. Broadly, these tests include annealing tests, tensile tests, conductor resistance tests, high voltage tests and insulation resistance tests.
Recent developments
The Central Electricity Authority (CEA) recently released an advisory for the implementation of the Bureau of Indian Standards’ standards and quality control orders (QCOs) related to aluminium ingots, wire rods and wires used for the manufacture of conductors/cables. These include mandates such as compliance with IS 5484 and IS 2067 for aluminium rods and wires, and IS 4026 for aluminium ingots.
The CEA guidelines suggest using high performance conductors (HPCs) with varied materials, including galvanised steel, zinc alloy and fiber-reinforced composites. Since many test facilities are unavailable in India, tests are often conducted abroad, increasing costs. Despite being two to three times more expensive than conventional conductors, HPCs can be cost-effective when accounting for associated costs and loss reductions.
Further, the CEA has recently issued new guidelines for testing the carbon fibre composite (CFC) core of high temperature low sag conductors. The CEA advises all power sector procurement entities to include the “galvanic protection barrier layer thickness test” as a mandatory requirement in their tenders, in accordance with ASTM B987 standards. It suggested that the salt spray test is not suitable for determining the thickness of the galvanic protection barrier layer on CFC cores, as there is no correlation between the two tests.
Conclusion
Advancements in technology, robotics and autonomous systems are set to improve the monitoring and maintenance of cables and conductors. These innovations will reduce health and safety risks for human operators. The industry and government are driving artificial intelligence and robotics development to gather asset condition data and assist technicians. Machine learning will efficiently process and analyse data on issues like corrosion and cracks. These technologies will enhance safety, reliability and cost-effectiveness, ensuring compliance with regulations. While electrical system errors are unavoidable, effective T&M can detect and fix faults before they become major problems, supporting a robust power network and reliable 24×7 power supply.