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Electric Energy T&D - Index

Electric Energy T&D - EE Magazine March / April - Index

Circle 40 on Reader Service Card
Then, nitrogen is injected (item 4) to have the whole transformer safe,
cool and ready for repairs. Note that additional DS can be placed in
order to protect the OLTC or the OCB (item 5).
III. THE EXPERIMENTAL CAMPAIGNS
Up to now, two test campaigns have been performed, both under the
worst conditions by creating low impedance faults leading to electrical
arcs inside the transformer tank dielectric oil. In 00 , Electricité de
France performed 8 tests. Then, in 004, a second campaign of
34 tests was carried out by CEPEL, the Brazilian independent High
Voltage Laboratory. This part presents the main conclusions of the
last test campaign performed on large transformer tanks.
A. The CEPEL experimental campaign
The 34 tests carried out in transformer tank dielectric oil by CEPEL
in 004 were performed in order:
• to study the vaporization process induced by an electrical arc and
the resulting pressure wave propagation,
• to evaluate a fast-direct-tank-depressurisation-based method to
prevent transformer tank explosions.
Three standard transformers were used for these tests. The
maximum distance between an electrical arc and the protection
system ranged up to 8.5 meters (28 ft). Various physical parameters
such as pressure, gas temperature, applied current, arc voltage
and tank acceleration were studied in details.
80 I March-April 2008 Issue
1) Experimental settings
Each transformer was equipped with:
• arcing generation devices to master the arc location and make
the tests repeatable,
• temperature probes,
• accelerometers, and
• pressure sensors at different locations in the transformer, in
order to study the pressure wave propagation.
The transformer protection, the TP, was also installed on each
transformer to study the ability to mitigate tank rupture by a tank
depressurization method based on the fast and direct passive
mechanical response of a depressurization set to the pressure wave.
Figure : Life Tests Transformer Principle Drawings