On-Line Transformer Treatment process:

Explanations & Case studies

On-Line Transformers Treatment Process

EN

D

What is the aim our Transformers Treatment Process: Treatment of transformer (dry the insulation materials by oil dehydration and circulation inside the transformer:

Moisture transfer frominsulation material to the oil.

90% of moisture is located inside insulation material and one of the method to remove this moisture is to warm the insulation material at a temperature at least 50°C to have the migration of the moisture from the insulation material to the oil. (CIGRE source)

The insulation material is warmed by the heating process of the oil inside the oil treatment plant. After the heating process, the oil will be dehydrated and after that the hot and dry oil will go back to the transformer, the calorie will be given to the insulation material, when the temperature inside the insulation material will achieve at least 50°C , the moisture from the insulation material will be transferred to the oil.

The moisture will be capture by the oil inside the transformer.

Moreover when the oil is hot, it increase it absorption capacity.

System of vacuum oil treatment without heater cannot perform this job, because the temperature inside the insulation material is not sufficient.

On-Line Transformers Treatment Process

Moreover ARRAS-MAXEI process use a special process of heating:

Advantage of the Gradual Heating Method:The scheme N°2 show the relation between the water in oil and the water in paper.

When we start the MAS 4000 TEC, we will move from point 1 to point 2 up the equilibrium point water/oil. After we will start the gradual heating method by heating the oil by 5° (point 2 to point 3), the water transfer from the paper to the oil start without any risk for the transformer (no free water).

More we heat the oil, more we accelerate the water transfer without any risk for the transformer (no free water).

In our case (transformer having 30 ppm water in oil at 50°C (3.9% in paper)), we are going to increase the temperature up to 85°C (oil) to obtain a water content inside insulation material below 1%.

On-Line Transformers Treatment Process

To be in good health, and avoid the ageing process of the insulation material, the percentage of moisture should be below than 3.3%, if it is more than 3.3% the transformer has to be dry.

On-Line Transformers Treatment Process

Dry transformer AcceptableAgeing paper process start« Flashover » possible at 90°C« Flashover » possible at 50°CLottery

0.5%2%3.3%4.5%7.0%>8%

Transformer characteristics% of moisture inside insulation material

It is difficult to measure the water content inside the insulation material, but we can have a link between water content in oil and water content in paper, you can find hereafter this drawing.

On-Line Transformers Treatment Process

Advantage of the Gradual Heating Method:Curve A: On-line Treatment without oil heating or coalescent cartridges

Curve B: On-line Treatment without gradual heating method

Curve C: On-line Treatment with gradual heating method

The scheme 3 shows that the gradual heating method reduce the time of treatment and the time to dry transformer.

The time will depend of the size of the transformer, weather conditions and water content.

To follow these parameters (temperature and water content in oil, we use online water ppm measurement probe to follow the evolution of temperature and water content in oil. (please see description in DT07.035/AE page number 5)

On-Line Transformers Treatment Process

Equipment : MAS 4000 TECCustomer : AES SONELLocation : Douala CAMEROONOn-line Treatment with MAS 4000 l/hBefore treatment: 30 ppm at 40°C % of moisture inside paper : 5%Gradual Heating Method up to 70 °C (oil)Vacuum 1 mbarTreatment duration: 3 weeksResult after treatment:Around 5 ppm at 50 °C % of moisture inside paper: below 2%

Case Studies

Case Studies

Equipment : MAS 4000 TECCustomer : EDF (French Electricity Board) Power PlantsLocation : Guchen FRANCEOn-line Treatment with with MAS 4000 l/hBefore treatment: 70 ppm at 31°C % of moisture inside paper : more than 15%Gradual Heating Method up to 65 °C (oil)Vacuum 1 mbarTreatment duration: 6 weeksResult after treatment:Around 21 ppm at 68°C% of moisture inside paper: below 2%