Flow electrification in power transformers: salt-type additive as a potential remedy?

Flow electrification in power transformers has been studied for the last 30 years, since the charge generation phenomenon was suspected to be responsible for power transformer failures. An experimental set-up has been built at the University of Poitiers in partnership with EDF (French utility) to simulate the oil path along the pressboard between transformer windings. The accumulated charge in a pressboard duct can then be estimated by the integration of the measured capacitive current up to infinite time. Among the investigations to reduce the electrostatic hazard, a chemical salt has been injected into new and aged oil at different concentrations. It was found that the accumulated charge was drastically reduced at different salt concentrations for both oils whatever the temperature and the flow rate applied.