*Power cables are one of the important parts of electrical power systems. It is important to know the materials that make up the cable or what the life of the cable will be at a given temperature. Therefore, aging tests are performed for the materials used in the cables. One of these tests is the thermal endurance test of the cable. The curve fitting process is performed to the data obtained as a result of this test and the temperature value (the temperature index) corresponding to the 20000-hour life of the cable is found. Automating the process of curve-fitting and finding the temperature index will be useful for companies or research centers that perform this test. Instead of expensive programs such as Matlab or Mathematica, the easy-to-use and accessible Excel program is a very economical and useful solution to evaluate these test results. In this study, the thermal endurance test was briefly described and a spreadsheet was prepared in Excel to evaluate the results of this test. Using the data taken from the measurements made for the EPR material, it has been checked that the spreadsheet works correctly. Such a spreadsheet can be easily used in cable factories to evaluate thermal endurance test results.*

### 1. Introduction

Power cables are commonly used for electrical power transmission [1, 2]. The cable insulations are susceptible to aging when exposed to the thermal, electrical, environmental, and mechanical stresses experienced under heavy operating conditions [3-5]. The insulation performance of aged cables decreases considerably [6]. That’s why insulation aging is an important issue enough to use the leakage current for its evaluation [7] or radio frequency signals for diagnosis of its location [8]. A review of the aging of extruded dielectric cables is presented in [9]. Aging Models for Electrical Insulation in Power Cables are given in [10, 11]. The aim of the tests is to predict the lifetime of electrical cables operating at elevated temperatures by applying the Arrhenius aging model on thermally aged samples [12]. One of the test properties used for thermal aging tests is the “Elongation at break test” based on two reference standards [13, 14]. The endpoint of the test property can be chosen as 50 % Elongation at break. Arrhenius equation is an exponential function and the least squares method is used to evaluate the test results or to find the parameters of the equation [4, 12]. It is time-consuming to use the least squares method by hand. It is important to automatize such test results. Although programs such as Matlab or Mathematica can be used for the evaluation of the results, they may be expensive for companies in developing countries. Microsoft Excel, part of the Microsoft Office suite, is a popular electronic spreadsheet program that provides a wide range of features for data manipulation, analysis, and visualization. Excel is widely used in business, finance, engineering, education, and many other fields due to its versatility and powerful features. Proficiency in Excel is considered a valuable skill in the workplace. The use of linear algebra in Excel provides various advantages and conveniences, making it a powerful tool for mathematical and analytical tasks. Excel simplifies matrix operations, which form the basis of linear algebra. You can perform matrix multiplication, find the inverse of a matrix, and easily manipulate matrices using built- in functions. Linear algebra is essential for solving systems of linear equations, and Excel provides functions and tools that efficiently solve a system of equations. An Excel spreadsheet is a grid of cells organized into rows and columns, where each cell can contain text, numbers, or formulas. Many engineering and social science problems are solved using writing macros or Excel spreadsheets [15-20]. A power-system analysis has been made with Impedances using spreadsheets [21]. It is shown that a commonly available spreadsheet package is usable to solve a three-dimensional heat flow problem for underground cable rating [22]. To the best of our knowledge, a spreadsheet has not been used to evaluate the aging test results. In this study, an Excel spreadsheet is used to calculate the parameters of the Arrhenius equation using experimental aging data.

The paper is arranged as follows. In the second section, the thermal endurance test is briefly described. In the third section, an Excel spreadsheet is prepared to calculate the parameters of the thermal endurance test. The paper is concluded with the conclusion section.

### 2. Brief Introduction to Thermal Endurance Test and Calculation of the Temperature Index

##### 2.1 Thermal Endurance Test

The experimental procedure of the thermal endurance test is briefly explained in [12]. The flowchart of the test procedure is given in Figure 1. Some results of thermal endurance tests performed on samples of EPR (ethylene-propylene rubber) cables are presented in [23, 24]. However, the endpoint of the test property for Extruded EPR Insulation Material is chosen as 50 % Elongation at break in this study. The properties are monitored under standard IEC 60216-2 [12].