Filtration of insulating oil

Filtration of insulating oil

There are mainly following three types of oil filter in common use.

1) Centrifugal purifiers

2) Stream line purifiers (Filter pack - up)

3) Activated earth media : Filter system.

Filtration of insulating oil

      

(1) Transformer

(2) Regulative valve

(3) Strainer

(4) Input pump

(5) Heater chamber

(6) Spray chamber

(7) Centrifugal bowl

(8) Drain valve

(9) Vacuum tank

(10) Vacuum pump

(11) Discharge Pump

(12) Outlet valve

The purpose of oil purification is to remove from it all the impurities or all contaminations such as water, carbon deposits, dirt, sludge, dissolved moisture and gases so as to improve its dielectric strength and give other properties required.

Out of the above the centrifugal purifier gives the best result. So it is explained on the basis of flow diagram.

The specific gravity of such impurities is more than the oil. In this method the oil is admitted into the centre of a bowl having number of conical shaped separating vanes fixed on the vertical shaft.

The shaft is coupled to a electric motor, which moves at very high speed 6000 to 8000 rpm. This causes high centrifugal forces on the heavier particles in comparison with oil particles.

This force is thousand times greater than the force of gravity and they are thrown outwards directly to the bowl wall and gets separated from oil.

When oil is centrifugal at high speeds it leaves the bowl in the form of extremely fine spray due to which evaporation of moisture takes placed and dissolved gases are released.

If high vacuum is maintained in the spray chamber and oil at high temperature is circulated in the chamber the process is accelerated and can be carried out at high rates.

Protection of electrical equipments during the period of inactivity

In the electrical equipments are kept idle or unused for at long time, the moisture condenses on the insulation. The moisture will get condensed at faster rate if the temperature of the machine falls below dew point.

The dielectric strength of machine insulation will decrease. Hence the temperature inside the machine is kept few degrees higher than the ambient temperature. It can be achieved

1. By using space heat.
2. Placing the electric lamps in the housing of machines to provide heat.
3. Cover the machine with water proof cloth during inactivity.
4. The brushes should be raised off the commutator and slip rings which prevents electrolysis between them and pitting the commutator or producing flat spots on metal surface.
5. Pour the insulation into the winding if required.
6. Run the machine during the period of inactivity even if not required.
7. 
   

Methods of cleaning insulation

The failure of insulation takes place due to absorption of moisture. Oil, dust, din. excessive heat, vibration, over voltage and aging are the main reasons for failure of insulation.

Removal of loose dust

The loose dust accumulated over the surface of winding, in the ventilating duct can be removed by applying compressed air at a pressure about 2.1 to 2.8 kg/cm from a portable vacuum cleaner. For this work the person should use mask, safety goggle etc.

Encrusted dirt

The encrusted dirt or sticky dirt can be removed carefully with a hard wood or fiber scraper, because the sticky dirt blocks mainly the ventilating ducts. A metal scrapper should not be used because it can damage the insulation.

Oily viscous film

The oily viscous film can be removed with a piece of cheese cloth. Use approved petroleum solvent. Don't use excess petroleum solvent which may damage insulation. Remove the oily film by cloth.

Cleaning with water

Cleaning of electrical machinery with fresh water and detergent. It is the recommended procedure for cleaning H class insulation. The cleaning should be done as rapidly as possible. The machine should be rinsed with fresh water, excess moisture wiped off with clean dry cloth and the machine should be baked in dry oven.