4 GSU transformer at thermal power plant

Nameplate data of the transformers:

Manufact: xxx
Year: 1997
Power [MVA]: 192
Voltage [KV]: 400
Oil mass [Kg]: 58.000
Oil type: naphthenic

May 2005

The analysis and subsequent diagnosis performed by Sea Marconi on the equipment of the customer showed:

Index of corrosiveness =1 (max level)
ASTM b 48H= 4C
Overall Health index: 0.52 (52%)

April 15, 2006

Failure caused by discharges of high energy

The high voltage windings clearly show the effects of the damage

April 19, 2006

Internal inspection and post failure analysis performed by Sea Marconi experts

Inspection after a failure with discharges of high energy due to corrosive sulfur
Visual map (included in Sea Marconi diagnosis) that shows in two-dimensional form the different levels of corrosion on the windings
Insulating papers on which is highlighted the presence of copper sulfide. Sulfide decreases in the inner layers

November 2006 – Solution

Solution: Selective depolarization treatment (Chedcos) by Sea Marconi performed on the twins transformers.

he treatment guaranteed DBDS < 10 mg/kg and at the same time the restoring of the other parameters according the IEC 60422 ed. 4, 2013

Before treatment

After treatment

DBDS [mg/Kg] 110 < 5
IFT [mN/m] 17 40
TAN [mg KOH/g] 0,133 < 0,01
DF 0,0448 0,0118

Identified Critical issues

Applied solutions

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