Substations are essential in the electricity supply system as they work as “links", allowing the connection of the power generating plants with the transmission lines, which, in turn, will connect, also through a substation, with the distribution networks. Thus, energy reaches all consumers.
Construction and operation of substations require specialized knowledge and, due to this, Neoenergia is expanding its technologies by developing a system for measuring the grounding resistance in substations, which reinforces the safety of operations by enabling a more accurate and safe diagnosis of the interconnection condition of the equipment to the substation grounding grid and, thus, generate more efficient maintenance.
Allied to this, the project is a pioneering investment in the development of a national technology that allows specific measurement even with the substation connected, something that is not possible with the systems currently existing in Brazil. The initiative is an achievement of the Research and Development (R&D) program of Neonergia, regulated by the National Electric Energy Agency (Aneel), and is in the stage of applying improvements to the product.
In order to better understand how the instrument under development by Neoenergia works, we need to understand the role of grounding in substations. Similarly to outlets in homes have a third pin, which serves as a ground wire for increased safety in the use of electronics and appliances, substations also have a grounding grid composed of rods and cables. This grid receives the electric current from the substation in the event of any occurrence, such as a short circuit in the equipment, preventing accidents and outages in energy supply. All substation equipment is interconnected to this grounding grid and, due to the amount of energy that flows through it, it is essential that the grid is in good condition so as not to affect the operation of the substation.
What Neoenergia system does is measure the resistance of the ground. If resistance is low, the grid is in good condition to absorb the electric current, as it has a free path to be received. In the case of high resistance, the maintenance team needs to intervene and identify why the grid is not performing as it should. This is usually done with the substation on, which interferes with the measurement equipment and provides an inaccurate diagnosis about the state of the grid, or is done with imported products, which are expensive and not always accessible. “Neoenergia's innovation is suitable for use in powered substations, as it was designed for this purpose, providing an accurate measurement, in addition to having the advantage of being affordable, as it will be manufactured in Brazil", says Neoenergia's project manager, Rogério Sá.
In order for Neoenergia's system to work, the measuring instrument is isolated and operates on a frequency other than the one existing in the substation, so as not to be subject to electromagnetic interference from the network. In addition, the instrument is operated remotely - either through a tablet or cell phone. Current injection is used to carry out the measurement, i.e., the current of electric energy is sent to the grid, where there are some sensors that measure the electrical voltage. Based on the data sent by the sensors, it is possible to make an accurate calculation of the grid resistance.
After a period, the ground suffers from the influence of the soil and the wear and tear of time, which can impair the quality of the grid. Therefore, it is important to measure the resistance on a periodical basis, in order to check it is in good condition, to ensure the balance of all equipment connected to it. This is the time when the role of preventive maintenance comes into play, by making diagnoses that allow identifying the state of the grid and directing efforts to carry out repair actions, such as replacing connectors and cables. "At this point, a specific measurement is very important, as this represents more assertive investments and reduces the cost of replacing damaged equipment, improving the company's indicators and adding safety", highlights Rogerio.
Neoenergia's project will be implemented in the more than 900 substations operated by company throughout Brazil. The initiative has already gone through the prototype stage, when the instrument was tested in several substations, and is now in the phase of improvements, implemented based on what was recorded during the tests. The project is expected to be completed by the end of 2023, when the product may be made available to the market. “We are nationally developing something that meets the needs of the electricity sector at an affordable cost, in addition to adding more features and technologies in a pioneering movement", concludes Neoenergia's corporate manager of Research and Development, José Antônio Brito.