Scenario

3 single-phase transformers installed in a thermoelectric power plant in southern Spain

Technical characteristics of the transformer:

Manufacturer .: xxx
Year: 1977
Power [MVA]: 216
Voltage [KV]: 220/22
Mass of oil [Kg]: 15,650 each.

Problem

Periodic analyzes of the oil showed a condition of hydration of the cellulosic insulation. The estimated water content in solid insulation is between 3 and 4% by weight, a typical condition for equipment with more than 30 years of service.

Solution

Sea Marconi performed the following activity:

Dehydration or drying of transformer (paper/oil)

The process was carried out with the transformer on-load under charge.

Detail of the phases of the intervention

  • Hydraulic connection of treatment equipment with temporary out of service transformer
  • Execution of the dehydration process with the transformer on-load
  • Disconnection of equipment with transformer on-load

 

Criteria for stopping treatment

  • Water in oil <10 mg / kg at t> 40 ° C
  • Breakdown voltage> 70 kV
  • Extracted water <250 ml / 24h

Treatment details

The process was carried out with the transformer on-load.
The temperature of the oil in the tank (top oil) was kept constantly above 70 ° C through the use of an auxiliary heating equipment.
Simultaneously the oil was recirculated through a vacuum dehydration equipment. Overall, about 15 liters of water were extracted from each device.

Duration of the intervention: 6 weeks (2 for each transformer)

Identified Critical issues


Applied solutions

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