"We can face the best passive protection and cooling system for underwater power electronics in the world, developed by Brazilians, for a Brazilian company." This is the expectation of Eng. Lucas Militão about the project Development of advanced systems for the protection and cooling of subsea electrical systems under high pressure, the second phase of which is awaiting approval from Petrobras to be carried out by researchers from UFSC (Universidade Federal de Santa Catarina/Federal University of Santa Catarina).

Fig. 1 – Lucas Militão on the laboratory bench

developed to evaluate the concept.

The first phase of the project, completed in September 2018, resulted in a technology that could help Petrobras relocate some equipment from oil platforms to the seabed, which would bring them closer to the extraction systems. "In addition to the fact that the equipment developed is compact and meets the requirements necessary for safe operation, preliminary results of a comparative analysis with commercial solutions have pointed out a considerable advantage for our equipment in terms of energy efficiency and weight", explains Militão. Your doctoral supervisor, Professor Jader Barbosa Jr., adds: “The geometry favors heat dissipation, which makes the system more compact and safer, in addition to being much more economical for assembly and installation on the seabed.”

Fig. 2 – Illustrative image of the annular envelope geometry proposed

in the project.

The application of this technology depends on adjustments and other procedures foreseen for the second phase of the project, under analysis at Petrobras. Although it is essential to test the news in real operating conditions, they are promising. "With some equipment closer to the extraction systems, there will be savings in resources, limitation to environmental damage and greater efficiency in the process", predicts Prof. Carlos R. Rambo, professor at the Department of Electrical Engineering at UFSC and project coordinator.

In addition to the innovation in terms of the cooling system enclosure geometry - which reduces the number of living corners and favors the natural circulation of the thermal fluid inside - the use of nanostructured thermal fluids improves the performance of the electrical systems installed on the seabed through increasing the dielectric protection and the heat exchange capacity of the system, increasing reliability and reducing size and costs.

As the depths at which electrical systems must operate reach 3,000 meters, the challenges imposed on researchers included designing and designing an electronic circuit and a cooling and protection system capable of withstanding high pressures - approximately 300 times atmospheric pressure - as well how to ensure that they do not require frequent maintenance, as this equipment will be installed in a place that is difficult to access.

This requires that the pressure inside the equipment be equalized with the external pressure - which requires the use of a specific device for this - as well as a cooling system without moving components. In addition, electronic components require special preparation to operate at such high pressures.

“Our project was extremely successful in this sense, not only because it shows, from laboratory tests and computer simulations, that it does adequate system protection and adequate thermal management, but also that it does not use moving parts in its design, which gives a high reliability to the group ”, points out Militão, involved in the project since he was doing a master's degree as a fellow at POLO (Refrigeration and Thermophysics Research Laboratories), one of those involved in the research.

One of the most recognized research units in the Department of Mechanical Engineering (Departamento de Engenharia Mecânica) at UFSC and headquarters of the National Institute of Science and Technology - Refrigeration and Thermodynamics, POLO created the cooling system for underwater power electronics. In the Electrical Engineering Department (Departamento de Engenharia Elétrica), INEP (Institute of Power Electronics) developed a power circuit that resisted the adverse conditions of ultra-deep waters, and LAMATE (Laboratory of Electrical Materials at UFSC) was responsible for the characterization and improvement of thermal and electrical properties of the dielectric fluid used in the subsea power circuits. 

All of this was aligned in joint meetings with Petrobras, in Florianópolis and Rio de Janeiro, before and after approval by the company, and the project was conducted under the administration of FEESC (Stemmer Foundation for Research, Development and Innovation).

While phase 1 allowed researchers to build the electrical system disposed inside a containment vessel containing nanofluids and test it under normal pressure and temperature conditions, phase 2, if approved, will aim to build the new steel containment vessel and test the electrical system in real operating conditions, under high pressure. For this, a hyperbaric chamber installed at CENPES (Leopoldo Américo Miguez de Mello Research Center) will be used. In addition, nanofluids will be subjected to long-term tests, in which aspects such as aging, stability and corrosive properties will be evaluated.


Legacy of years of reaserch

Among other contributions, the project has already enabled the training of qualified human resources to work with electrical power systems for subsea applications, nanotechnology and advanced materials, as well as heat transfer processes, aiming at energy efficiency and improving thermal and dielectric protection for these electrical systems. It also increased the research capacity of LAMATE, INEP and POLO, by setting up a basic infrastructure for characterizing materials for the Oil, Gas and Energy sector.

“This infrastructure makes the laboratory network particularly independent and unique in the country. Through a solid integration with Petrobras, the idea is to transform UFSC into a reference pole in the characterization of advanced materials for the Oil, Gas and Energy sector ”, concludes Prof. Rambo, LAMATE supervisor, graduated in Physics from USP (University of São Paulo), with a master's degree in Nuclear Technology-Materials from USP and a sandwich doctorate in the same area, part at USP part at FAU (Friedrich Alexander Universitat Erlangen-Nurnberg), in Germany.

Original article in: Divulgação EMC/UFSC

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