Table of Contents
Overview of HV Cable Current Rating Calculations
Accurately calculating high voltage cable current ratings is critical to electrical engineering design, ensuring power systems’ safe, reliable and efficient operation. The IEC 60287 standard series provides equations for calculating cable current ratings. This standard continues to be widely adopted because: 1. It is adapted for common cable types and installation methods. 2. It is reasonably accurate, which leads to reliable, current ratings for new and existing cable circuits. 3. It ensures consistency, dependability, and comparability of current ratings determined by different bidders, providers, or suppliers for stakeholders.
New methods (that are less conservative than those from IEC 60287) to calculate the cable losses in three-core armoured cables was introduced with CIGRE Technical Brochure 908 (2023). This technical brochure provides improvements to the IEC 60287-1-1 loss factor empirical equations, which are based on early research performed on cables with small conductor cross sections and common sheath. The effect of outer metallic layers on the electrical properties of inner layers is discussed and elaborated with examples. In general, for three-core armoured cables the current rating is increased by approximately 10 %.
Introduction to ELEK Cable HV Software
To meet the needs of industry, Electrotechnik developed a specialised software, ELEK Cable HV, designed to accurately calculate high voltage cable current ratings in accordance with the internationally recognised IEC Standard 60287, and whose results have been validated with CIGRE TB 880. The software also incorporates the finite element technique for performing calculations beyond IEC 60287 limitations.
ELEK Cable HV is powerful and easy-to-use software widely adopted worldwide. To read about the full range of technical features or download the software, visit the product page.
Validation Process
The validation process undertaken to compare the results of ELEK Cable HV with the seventeen (17) case studies in CIGRE TB 880 involves the following detailed steps:
- Understanding CIGRE TB 880: Gain a deep understanding of the forty-nine (49) guidance points, methodologies, equations, and case studies presented in the brochure, as they serve as the benchmark for validation.
- Selection of case studies: We have chosen to validate against all case studies.
- Modelling of the cables: Eleven (11) different cable types require detailed models. The cable layer dimensions, material types, and properties must be matched. Special custom layers were required, including those for water-blocking tapes, semi-conductive outer coatings, copper woven fabric tapes, polyethylene sheaths around each core, custom filler materials, polypropylene yarn, hollow or Milliken conductors, double steel wire armour, metal pipes with coatings, multi-layered (with different thermal resistivities) paper insulation, and sector-shaped conductors.
- Calculation execution: We used an iterative calculation process with an optimisation algorithm. To match the results of the technical brochure, we have used the same strict convergence criteria of 10-10 for final temperatures and final current ratings. Furthermore, for the HVDC case studies, the temperature drop across the insulation was also considered a dictating factor for current ratings.
- Result comparison: There is no reason for any differences in the final current rating or the intermediate results of the calculations of the case studies (Section 3 of CIGRE TB 880). The final and the intermediate results must match exactly.
Results and Findings
Case study 0.1.1: Direct buried 132 kV cables. This case study consists of 132 kV cables in direct buried trefoil formation. Sheath is single point bonded.
Case study 0.1: Direct buried 132 kV cables. This case study consists of 132 kV cables in direct buried trefoil formation. Sheath is solidly bonded.
Case study 0.2: Buried 132 kV cables. This case study consists of 132 kV cables in direct buried trefoil formation in separate ducts.
Case study 0.3: Buried 132 kV cables. This case study consists of 132 kV cables in direct buried flat and spaced formation in separate ducts.
Case study 0.4: 132 kV cables in air. This case study consists of 132 kV cables in air installed on non-continuous brackets, ladder supports, or cleats. Sheath is solidly bonded.
Case study 0.5: 132 kV cables in air. This case study consists of 132 kV cables in direct buried trefoil formation and direct buried flat formation.
Case study 1: Direct buried 132 kV cables. This case study consists of 132 kV cables in direct buried trefoil formation and direct buried flat formation.
Case study 2: 30 kV submarine array cable. The cable type is a three-core submarine cable with copper round compacted conductors, XLPE insulation, lead alloy sheath, semiconducting polyethylene sheath, polypropylene yarns, galvanised steel wire armour and polypropylene yarns.
The same case was modelled but with the armour losses recalculated according to CIGRE TB 908 and the result was an increase in current rating by 8.89 %.
Case study 4: 33 kV land cable. Buried cable design with less than 50 % cover of screen wires.
Case study 5: 400 kV low-pressure oil-filled cable with a 2000 mm2 copper conductor and corrugated aluminium sheath buried in trefoil and flat formation.
Case study 6: 400 kV single core AC submarine cable circuit. Lead alloy sheath.
Case study 9: 110 kV retrofitted cable. The cable type is a XLPE-insulated three-core cable with round stranded copper conductor, aluminium-polyethylene-laminated sheath and steel wire armour in a PE-covered steel pipe. Case study 9 current rating results differ by 0.68 % because there is a minor mistake in CIGRE TB 880 with their T2 thermal resistance calculation.
Case study 10: 10 kV three core PILC cable. The cable type is a three-core paper insulated cable with aluminium sector shaped compacted conductor, mass impregnated paper insulation (unscreened), common lead sheath with steel tape armour and PVC outer sheath.
Benefits of ELEK Cable HV Software
- Accuracy and Reliability: With matching results obtained during validation, users can trust that ELEK Cable HV delivers precise and reliable current ratings. This accuracy ensures the safety of personnel and equipment while maintaining the reliability of the electricity network.
- Time and Cost Efficiency: By automating the complex calculations required for cable current ratings, ELEK Cable HV streamlines the design process, saving valuable time and effort for electrical engineers. It enables efficient resource utilization, eliminates the need for manual calculations, and minimizes the risk of errors or miscalculations.
- Compliance with Industry Standards: Our software is developed in strict adherence to IEC Standard 60287, ensuring compliance with internationally recognized guidelines for high-voltage cable current rating calculations. This compliance guarantees compatibility with industry practices, regulatory requirements, and project specifications.
- Flexibility and Customisation: ELEK Cable HV offers flexibility and customisation options to accommodate various cable configurations, operating conditions, and project-specific requirements. It allows users to input specific cable and installation details, facilitating accurate calculations tailored to the specific design needs. The finite element technique further extends the capabilities.
- Comprehensive Reporting and Documentation: The software provides comprehensive reporting capabilities, allowing users to generate detailed reports of the calculated results, assumptions made, and input parameters used. This documentation ensures transparency, traceability, and engineering standards and practices compliance.
- Continuous Updates and Support: We are dedicated to continuously improving and upgrading ELEK Cable HV to incorporate the latest advancements in high-voltage cable current rating calculations. We provide ongoing support, ensuring that our users have access to the latest software versions, updates, and technical assistance.
Conclusion - ELEK Cable HV successfully validated
The successful verification of ELEK Cable HV against the CIGRE Technical Brochure 880 is a significant milestone for our software, highlighting its accuracy and reliability in calculating high voltage cable current ratings. The accuracy of the results for three-core armoured cables has been further enhanced with CIGRE Technical Brochure 908.
Achieving exact matching results with the industry-standard Technical Brochure demonstrates the meticulous attention to detail and commitment to excellence in our software development. With the validation process completed, ELEK Cable HV provides electrical engineers and professionals with a trusted and efficient tool for accurate high voltage cable current rating calculations, ensuring power systems’ safe and optimal performance.
