OneLine Engineering carried out a study to determine the cause of a failure of reactive compensation capacitors and the failure of the associated series reactor connected to the tertiary winding. The scope of work included:
• Collection of available data at site
• Setting up a simplified model of the power system to estimate the magnitude of voltage variations due to capacitor switching
• Use of the model to identify possible resonance frequencies
• Development of a Bewley lattice diagram to investigate the possibility of over-voltages due to wave reflections
• Review of data extracted from the existing multifunction relay to determine the possible presence of harmonics
• Determination of the adequacy of surge arresters protecting the transformer delta tertiary circuits and capacitors
• Ascertain the effectiveness of the existing grounding system
• Detailed design for the installation of new reactors
• Detailed equipment and installation estimate