Informations

Operating and Maintenance Instructions of Transformer Oil

In the transformers, mineral oils are used as insulation and heating. These oils, exidize over time due to air exchange.There are two reason that;

1) May discharge occurs based on several reasons between the active elements of the transformer.

2) May occur temprature differences according to power.

Consequently, The mud occurs to bottom of the transformer. Because, fragmented materials fall down in the transformer. If transformer has not air dryer or if it has never seen maintenance, trasnsformer take maisture from expansion reservair.

For this reason,oil loses insulation properties, therefore, oil should be check acoording to both TS 623 (Neutralization number) and VDE 0370/9.61 (Breakdown Voltage).

Neutralization number of the oil indicates 1g necessary to connect the oil acid (KOH) how many mg amount. This value should not exceed 0,05 mg KOH/gr for nwe oil. According to VDE instructions, if neutralization number is greater than 0.6 this oil must change or must refine.Purification process need to layout so preferre changing the oil. Oil breakdown coltage must be mezsured to determine the degree of moisture in oil. Breakdown voltage of the oil is finding to oil measuring between two containers(20 °C). This value is 2,5 mm and electrode spacing VDE 0370/9.61.

If periodic maintenance is made of a transformer and adequate protection is made of a transformer, breakdown voltage of the oil does not fall below from these values. Nevertheless, if these values are decreasing, oil has absorbed moisture, while oil is taking the sample.

According to VDE instructions, breakdown voltage should be 50 Kv/2,5 mm for new transformers. Oil should be dried, if values are decreasing 40 Kv/2,5 mm.  

DRYING OF TRANSFORMERS

   If a transformer's oil is below of these values, the oil is judged as a moist. In this instance, contrained within in theoil paper,paper bound, paperbound and wood have to moisture. So, these should dry with oil. Generaly, changing the oil of the small transformers is more economical. So, instead of drying, replacement is recommended.

HOT INJECTION METHOD

This method can use to speed up drying in the durable boilers oil is not heating more than 80°C, we can choose pressure according to oil temprature, in which is given below ruler;

If moisture is high in the oil, should clear water and mud from bottom of boiler. Oil from bottom of the transformer, it is pumped to heating and spraging system by oil pump.

Water is dissociate more easily from oil with spray system, water evaporates and it is thrawn out. Also heavy oil passes through the filter then back to the transformer tank.