ENDE Transmisión, a subsidiary of ENDE Corporation, operates as a transmission utility in Bolivia’s National Interconnect System, which provides connections between generating plants, distribution networks and non-regulated customers throughout the country. ENDE Transmisión’s system is, for the most part, made up of overhead lines but it also operates some relatively short underground cables which, although they are more costly to install, are less affected by adverse weather and have superior fault performance.
In the past, the utility used the services of a third-party company for testing and commissioning its EHV and HV underground cables, but it recently became convinced that this was not the best solution. The third-party service was very expensive and the results were not always dependable. For example, commissioning included a 24-hour soak test carried out at the nominal working voltage of the cable, but engineers at ENDE Transmisión considered that the results of this test were not necessarily indicative of the true condition of the cable.
As a result of these concerns, ENDE Transmisión decided to purchase the necessary equipment and carry out its own cable tests. It was hoped that not only would this approach ultimately save money, it would also give the utility’s engineers greater insights into the operation and maintenance of underground cables.
After examining a wide range of cable test options, including resonant-wave and nominal voltage testing and carefully analyzing the requirements of the the IEC 60840 and IEEE400.4 standards, ENDE Transmisión decided that its requirements would best be met by test equipment that used damped AC voltage (DAC) technology. This would be much less bulky than the resonant test system that had been used by the third-party service provider, but would be capable of providing comparable and, in many cases, better results.
This decision was followed by an in-depth survey of currently available DAC test equipment, which concluded that the Megger DAC300 would be the most suitable option, as will would be ideal for commissioning and acceptance testing of new cables. In addition, it would also be useful for locating partial-discharge faults in cable accessories and in the insulation of all types of EHV and HV underground cables, whether those cables were new or service-aged. This was an important benefit as increased partial discharge activity is widely accepted as being one of the best indicators of insulation degradation in cables.
An opportunity for ENDE Transmisión to try out its new cable test equipment and verify its performance in harsh operating conditions came when the utility needed to test a 20 km (12.4 mile) long 115 kV underground cable supplying the Yacimientos de Litio Bolivia (YLB) lithium production plant. This plant is located at an altitude of around 3,700 m (12,000 ft) above sea level in the middle of Salar de Uyuni, which is the world’s largest salt flat and contains between 50% and 70% of the world’s known lithium reserves.
The climate in Salar de Uyuni subjects equipment to severe challenges. The atmosphere is arid, the environment is salt-laden, with strong and unremitting sunshine. These conditions combine to encourage corrosion and, to avoid this, it is highly desirable for all testing to be completed in the minimum possible time.
The Megger DAC300 offers important benefits in this respect, as it produces detailed and reliable results in a much shorter time than is possible with most other test techniques. The DAC300 is also ideally suited for use on site, as it is compact, readily portable, easy to set up, and it requires little power for operation.
As this was the first time the engineers from ENDE Transmisión had carried out tests using the DAC300, on-site support was provided by Hein Putter of Megger to ensure that operations went smoothly. The tests were carried out on April 9, 2018 and were completely successful – the cable under test was found to be in excellent condition and ready to be put into service.
Marcelo Hinojosa, Head of Maintenance and Operation at ENDE Transmisión, was so pleased with the performance of the DAC300 and with the results it delivered that he posted about it on Facebook, with pictures and the caption, “Commissioning test of the 115 kV underground cable at Litio-Salar ENDE’s Transmission Substation – for the first time in Bolivia and South America.” Ben Lavis, Megger’s Director of Sales for Central and South America, added, “Marcelo was delighted that the test went so well, and also that it proved the DAC300 to be an excellent solution for cable testing that delivers big cost savings, now and in the long term.”