Scenario

Hydro Power Plant

The transformer is located near a river dam with extreme logistical and environmental constraints. The option of changing the oil was discarded immediately because of the enormous difficulties in handling (see. Photo) around the transformer. At the same time the fuller earth techniques would not solve the functional criticalities of the system “oil – transformer”.

Nameplate data of the transformer

Year: 1969
Power [MVA]: 105
Voltage [KV]: 225
Oil Mass [Kg]: 29.000
Oil Type: paraffinic non inhibited

Problem

For this case, Sea Marconi has done a detailed study using multidetection diagnostic tools from which emerged the following critical factors:

  1. PCBs above the threshold due to cross contamination caused by previous treatment performed by unskilled operator in a sensitive environment (water for cultivation)
  2. Corrosion C2 (NON DBDS & Corrosive sulfur) with DBDS equivalent = 70 mg/Kg and CCD test result as corrosive without DBDS
  3. corrosion C4 (NON sulfur corrosion & metal dissolution), due to presence of copper in organ metallic form
  4. dielectric properties of oil non standard

there are no electrical faults, there are thermal defects but only a normal aging of the insulation solid

Solution

Sea Marconi proposed and performed and integrated treatment based on selective depolarization (Chedcos) and dehalogenation of PCB in oil (CDP Process). The treatment was performed on-site and on-load (transformer in service and under load) with a total duration of 22 days, of which 16 for the treatment part.

The solution Sea Marconi won and convinced primarily for the modularity of the treatment unit (DMU), with reduced weight and size and therefore extremely easy to handle in an area with extreme logistical constraints.
Not only, the service Sea Marconi was able to heal, with just one treatment, the problems of corrosivity and the problems of PCB contamination, both the poor dielectric oil.

Before the treatment

After the treatment

Acidity TAN [mgKOH/g]

0,281

< 0,01

Interfacial tension [mN/m]

18,08

33,30

Moisture [mg/Kg]

6

2

Dissipation factor 90 °C

1.023

0,09211

Breakdown voltage [KV]

73,10

75

DBDS [mg/Kg]

< 5

< 5

Corrosive sulfur CCD test

corrosive

Non corrosive

Total corrosive sulfur (DBDS equivalent) [mg/Kg]

69

8

Copper [mg/Kg]

64

2

PCBs [mg/Kg]

71

25

The brilliant results achieved are the result of a mix of excellence:

  • Innovation and technical treatment plants and transformer oil,
  • the use of specific reagents patented,
  • the competence of technicians Sea Marconi,
  • certification of the analytical test results

This case brings together a number of peculiarities that make it unique worldwide. It has required a major effort to research, development and innovation. This has generated a series of advanced methodologies focused to multidetection; moreover this case has allowed us to study new treatment methodologies and instrumental configurations for monitoring entirely new.

Since this case is expected to publish some results in trade magazines from IEEE and Analitcal chemistry.