TGV (Train à Grande Vitesse) 25kV power line transformer North of Lille owned by SNCF.

Off-line filtration, round the clock oil treatment, purification and drying of the oil and eventually the insulators of the transformer. By doing so increasing the breakdown voltage and lifetime of the installation.


Drying of the oil utilizing absorption methods, above photo during pre-filling of the unit with new transformer oil Shell Diala B Dried.

The Buchholz-relay, mounted between the transformer and conservator tank.

----------------------------------------- side note -----------------------------------

Buchholz relay

In the field of electric power distribution and transmission, a Buchholz relay is a safety device mounted on some oil-filled power transformers and reactors, equipped with an external overhead oil reservoir called a "conservator". The Buchholz relay is used as a protective device sensitive to the effects of dielectric failure inside the equipment. A generic designation for this type of device is "gas detector relay".

Two ball-shaped floats and two glass-enclosed reed switches are visible inside this cutaway view of a Buchholz relay. Source:



Above: Suction connection on the transformer, at that time the temperature reading showed 3,2C.


Above: The return line connections to the transformer.


The measured Breakdown Voltage of 75kV of the new oil.

2009 10 05 SNCF Lille installation CJC unit Oct09 018

Purpose of the oil treatment was to restore the Breakdown voltage of the oil in the transformer by reducing the water content, removal of particles and adsorption of oxidation products.

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