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Verification of Dynamic and Cyclic Simulations

In the verification report of Grøft Design® with the Technical Brochure (TB) 8801, the software was proven to reproduce, with a high accuracy, the current ratings of power cables for steady-state operation calculated with the theoretical models based on the IEC 602872. However, no corresponding guidance or verification covering dynamic and cycling rating has yet been released by CIGRE.

As for now, the rating of the power cables with variable load relies on the IEC 60853-23 and the IEC 602872, which cover only limited cable installations and operating conditions, as discussed in verification report of Grøft Design® with TB 880

Scope of the Study

The Grøft Design® software was verified with the IEC 60853-23 standard for the transient current rating calculations. Due to the limitation of the IEC 60853-23 standard for the analysis of more complex loading patterns, apart from the single emergency step-load or 24-hour cycle, the IEC formulas had to be supplemented with the principle of the superposition which enabled the analysis of the cable temperature response to the multiple-step load.

The results obtained with GRØFT were compared with the analytical models. Furthermore, a case study considering real-life cable installation was analyzed. The data gathered from field-measurements (Distribute Temperature Sensing) was compared with a simulation carried out in the Grøft Design® software.

Discussion and Conclusions

The analyses performed in Grøft Design® and presented in this report gives results that are in line with the IEC standards.

The IEC standards are, however, limited to basic cable installations4. Grøft Design® supports analyses of much more complex cable arrangements with a lot of flexibility in defining the boundary condition, both stationary and time-varying. It is worth pointing out, that the user benefits from the increased accuracy of the FEA engine provided by Grøft Design® compared to analytical models.

A key advantage of Grøft Design® is the increased accuracy provided by its full FEA solution, which surpasses analytical models in precision. This is particularly beneficial in scenarios where standard analytical approaches may introduce simplifications that impact the reliability of the results. Furthermore, the dynamic load module opens the possibilities for correlating the models in the software with field measurements considering the varying load and the reference conditions. This will be the main focus of the ongoing INCA research project.

Verification Report

The complete report, “Dynamic rating calculations: Verification of Grøft Design® with the IEC 60853-2 and engineering practice”, is found here.

Sources

Footnotes

  1. ​CIGRE, TB 880: Power cable rating examples for calculation tool verification, WG B1.56, 2022. ↩

  2. NEK IEC 60287-1-1:2006 Calculation of the current rating Part 1-1: Current rating equations (100% load factor) and calculation of losses, Norsk Elektroteknisk Komite. ↩ ↩2

  3. NEK IEC 60853-2:1989 Calculation of the cyclic and emergency current rating of cables ↩ ↩2 ↩3

  4. CIGRE, “A Guide for Rating Calculations of Insulated Cables ” Workin Group B1.35, December 2015. ↩