Diagnostic tests of cable lines are an essential element of ensuring reliability and optimal efficiency of telecommunications systems. As the network infrastructure is becoming more and more complex, and the needs of users are growing, regular and precise monitoring of the condition of cable cables becomes crucial for maintaining the quality of services. In this article, we will discuss the most important methods and tools used in the diagnosis of cable lines, including damage location techniques, analysis of signal parameters and assessment of the technical condition of the cables. We will also present how proper research affects the efficiency of the network, allows early detection of problems and optimizing the costs of maintaining cable infrastructure.
Main assumptions of diagnostic tests of cable lines
The main assumptions of diagnostic tests of cable lines include detailed procedures aimed at assessing the technical condition of power cables, both newly built and existing. The key element is the use of testing tensions, which must be adapted to the value of the rated voltage of the line and a certain test time, in accordance with the adopted standards. The value of the test voltage should not exceed 1.3 UO, although voltages of other shapes and frequencies are allowed.
The tests include measuring the dielectric loss factor (TGδ), which provides information on the state of cable insulation, including the degree of moisture and the aging process of insulation. When laying, naturally use equipment as a corner roll to avoid damage, but further operation is another matter. In addition, measuring incomplete discharges allows you to identify places with weakened insulation parameters. In both cases, the tests should be carried out after laying cables and installation of accessories, with a voltage not higher than 0.7 UO.
Before starting the research, it is necessary to obtain the consent of the owner of the line, which must be informed about the research methodology, expected effects and potential threats to the life of the line. When using voltages exceeding 1.3 UO, additional receiving tests are required in terms of voltage cable insulation test to ensure the safety and integrity of the entire system.
How often is tests of cable lines?
The frequency of cable lines tests is strictly dependent on the technical condition and type of cable line. For new, repaired or rebuilt cable lines, it is recommended to perform basic tests and diagnostic tests, depending on the insulation used. In the case of lines with PE and XLPE insulation, these tests are obligatory, while for pilc insulation cables are recommended after repairs or reconstruction. Overhead lines, made using equipment such as a belt winch, are more exposed to damage, but this does not mean that the cable line does not need to be controlled in terms of technical condition.
After performing the first diagnostic tests, another test should be carried out every 10 years, assuming that at least 40% of the line length is a new cable. Subsequent diagnostic tests should be carried out every 5 years, unless the results of previous tests suggest a shorter period. However, in the case of cables up to 50 meters long, diagnostic tests are not mandatory.
In relation to cable lines in current operation, regular diagnostic tests are necessary, in accordance with the established cycles, and in cases where special circumstances indicate this, such as the significance of objects powered from a given line or the impact of failure on the indicators of the reliability of Saidi and Saifi. Operating measurements for cables that have undergone previous diagnostic tests should also be performed every 10 years or in 5-year cycles, unless previous test results indicate the need for them more often.
Tests of high voltage cable lines
Cable lines tests play a key role in the diagnosis of the technical condition of cable insulation, which is necessary for effective system management and planning preventive activities. Thanks to these studies, the likelihood of failure and effectively plan the modernization of cables can be significantly reduced. These tests should be carried out for all new, rebuilt and repaired after failures of WN cable lines, and their purpose is to assess the condition of the insulation and functionality of cables. With high voltages, cable lines are increasingly used because they are safer compared to overhead lines, which are built using equipment such as a cable lipstick.
The first key test is to measure insulation resistance. Before its execution, thoroughly clean the outer surfaces of the cable heads according to the manufacturer's recommendations. The cable should be unloaded and grounded for at least one minute before the measurement. Measurement of insulation resistance is performed for each cable vein relative to other veins and grounding, using a 2.5 kV meter. The value of resistance in a state set in a 1 km long line should be at least 1000 mΩ for cables with polyethylene or paper insulation. The insulation resistance for other cable length is converted into 1 km long in accordance with the appropriate pattern.
Another important measurement is to measure the resistance of the main and return veins, which aims to check the correctness of cable vein connections. This measurement is performed for new lines and after repairs, using a bridge or technical method using a direct current source. For cables with a voltage of 110 kV, the technical method with an upright current with a value of at least 60 A is used, eliminating the contacts resistance on the outer parts of the cable heads.
The last important test is the voltage test of the main insulation. The voltage value, its course and frequency, as well as the time of application are crucial for the assessment of the electrical strength of the insulation system. Among the available test systems, there is a sinusoidal voltage with a network frequency or oscillating DACs, which are used to thoroughly assess the quality of the cable line.
