The causes of a number of explosions of EHV current transformers in service on the Hydro-Québec 765 kV network have been investigated. Thermal runaway related to unexpectedly high dielectric losses in one of the oils used was diagnosed. Electrical instability of the oil was related to dissolved-metal content rather than to oxidation. A new way of stabilizing the oil is proposed, consisting in the...
Some discharging effectiveness was found in the oil tank system equipped with 100 or 200 mesh stainless screen fixed on top of the diffuser at the oil inlet. To study the discharging mechanism in detail, the potential distribution along the axis of the cylindrical oil tank, the earth current in each part of the oil-flow system, and surface potential of the oil tank were measured.
Financed by the National Centre for Research and Development under grant No. SP/I/1/77065/10 by the strategic scientific research and experimental development program:
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