Power utility Eletrobras Furnas had no way of accurately measuring the heat in their HVdc converter station, and it was affecting their ability to provide reliable power.
Consequences could include damaged equipment and instability to the Brazilian power grid. Furnas wanted to proactively address the issue, but a solution didn't exist.
The Paraná River carves a vein-like, 3,000-mile path through Brazil, Paraguay, and Argentina. Along its path, the river joins the countries of Brazil and Paraguay and passes through the Itaipu dam before continuing its journey south.
Itaipu is an impressive power source. It produces the largest amount of hydroelectricity in the world, setting a world record in 2016 of over 103 million MWh in annual generation.
Itaipu has 20 generator units—10 that produce energy for Paraguay at 50 Hz and 10 that produce energy for Brazil at 60 Hz. Paraguay’s modest power requirements result in a large portion of unused energy from their generators. Paraguay transmits the energy to Brazil through short ac (50Hz) transmission lines, where it is converted to dc in a substation close to Itaipu. Once converted, the energy is transported via HVdc transmission lines 810km to the Ibiúna substation in Brazil, where it is inverted from dc to ac (60 Hz). The inversion process introduces harmonics which have the potential to destabilize the power system. Stabilizing this inversion process was crucial for Eletrobras Furnas to reliably transmit energy for more than 2 million households.
Harmonics are a natural part of any inversion process. However, they must be filtered out before that energy is injected into the power system. Harmonics raise the level of heat, interfere with communications and control, cause bad power quality, and lead to loss of life in motors. Eletrobras Furnas installed filter banks at Ibiúna in an effort to remove these harmonics (and to provide reactive power to the conversion process), but the filters were unable to operate as designed, and the continuity of service was being jeopardized.
The problem was in the protection scheme. For years, Eletrobras Furnas used a root-mean-square (rms)-based scheme as overload protection for the filters. While an rms scheme associates all currents, fundamentals, and harmonics, flowing into a filter, they do not separate load levels at different harmonic frequencies. The inability to accurately measure heat generated by the harmonics in the filter banks jeopardized the HVdc converter. If there is no harmonic filtration, the inversion process shuts down. If there is no inversion process, there is no transmission of energy.
After analyzing the filtering process, their equipment, and other system requirements, a potential solution became clear to Eletrobras Furnas. They needed protective devices with logic that could separate out load levels at different harmonic frequencies and accurately calculate the heat generated within the filter banks. The only problem was that an off-the-shelf solution wasn't available from any company. But when they reached out to SEL with the specifications of their proposed solution, they learned about the beauty of SELogic control equations.
SELogic equations are flexible. SEL engineers created new SELogic functions tailored just for Eletrobras Furnas and implemented the solution in the SEL-734 Revenue Meters and SEL-451 Protection, Automation, and Bay Control System Relays.
Instead of compromising, Eletrobras Furnas got a solution that can calculate the load levels based on each harmonic frequency and accurately measure the heat generated by each fundamental and harmonic current. Now, harmonic filtration is smooth, overcurrent and overload protection is reliable, and Brazil and Paraguay benefit from a truly unique solution—proposed by Eletrobras Furnas, designed by SEL.
With this new protection scheme, we were able to predict the overload in the reactor really precisely, which solved the problems Eletrobras Furnas had in the past.