Magazine | Issue 1 2025 New circuit breaker technologies, particularly vacuum circuit breakers (VCBs) rated from 72,5 kV up to 420 kV, have been launched or are entering the market. They’ve been considered stateof-the-art in medium-voltage grids for decades. However, whether this advancement is also occurring in highvoltage (HV) grids remains an open question without a definitive answer. Vacuum technology promises minimal maintenance, long operational life, and environmental friendliness. The environmental angle has become increasingly vital due to impending updates to the EU F-Gas Regulation, which aims to ban and restrict the use of fluorinated greenhouse insulation gases like SF₆ to reduce greenhouse gas emissions. Phenomena: “pre-strikes” and “multiple re-ignitions” Interactions with vacuum technology in medium-voltage circuit breakers have revealed “pre-strikes” and “multiple re-ignitions”. › “Pre-strikes” occur during closing operations. › “Multiple re-ignitions” occur during breaking operations, accompanied by “current chopping”, where the current is interrupted before the AC current naturally crosses zero. These processes emit steep fronted transient voltages and current impulses, causing non-homogeneous voltage distributions inside adjacent assets and over-voltages that cause higher dielectric stress. What about high voltage grids? Until now, very little is known about combining HV grids with the measured electrical stress caused by vacuum CBs. This knowledge gap has motivated utilities to gain operational experience under realistic conditions throughout a VCBs lifetime. High-frequency transients are particularly undesirable because they can harm insulation systems and affect inductive components such as shunt reactors or current transformers in the grid. These transients can lead to significant internal overvoltages and stress on the electrical infrastructure, resulting in potential equipment failure or reduced lifespan. Utilities looking to apply these new technologies in their standard highvoltage applications usually install pilot installations to gain more confidence. Part of that is evaluating the need for countermeasures, such as adding circuits that dampen transient signals. We’ve supported pilot projects with our knowledge and expertise by specifying required voltage measurement systems, selecting appropriate technology, and generating meaningful reports throughout the one-to-twoyear evaluation period. Voltage measurement system specification Selecting the appropriate instrument transformer is essential when capturing true signals in the electrical grid. Conventional voltage transformers (VTs), which operate on the inductive principle, are designed for grid frequency and are incapable of capturing transient voltage signals. CR-dividers are recommended for measuring transient signals. These devices are capacitive and resistive components connected in series and belong to the low-power instrument transformers (LPIT) class. The capacitive component offers high accuracy across a wide frequency range, from 50 Hz to lightning-impulse voltage frequency, while the resistive component uses 25
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