TRANSFORMER OIL

TRANSFORMER OIL AND ITS PROPERTIES?DETERIORATION OF INSULATING OIL?

PRECAUTION AT A TIME OF TAKING OIL SAMPLE?

TRANSFORMER OIL: This is a synthetic mineral oil.It is prepare from fractional distillation of crude petrol.This is also known as mineral oil, insulating oil, switch gear oil etc.

Transformer oil

This is used for cooling,insulating, arc suppression in different electrical equipment like transformer, circuit breakers, switch gears etc.

PROPERTIES OF TRANSFORMER OIL: 

The properties of transformer oil is given below,

1.High specific resistance: They should be high specific resistance.Due to this insulating capacity of oil increases.

The minimum specific resistance at 90°C = 13*10¹² ohm–cm

The minimum specific resistance at 27°C = 500*10¹² ohm–cm

→ On increasing temperature the resistance of insulator decreases.

2.High dielectric strength: The dielectric strength of transformer oil means the maximum voltage at which transformer oil works without breakdown.

The minimum dielectric strength of transformer oil before use = 30 kV

The minimum dielectric strength of transformer oil after use = 20 kV

The maximum dielectric strength of new transformer oil = 55 kV

3.High flash point: The flash point of transformer is defined as the minimum temperature at which oil form vapour near its surface and it ignite or produce spark, when it comes near fire.So, the transformer oil should be high flash point.

The minimum value of flash point of transformer oil is 140°C.

4.High fire point: The minimum temperature at which transformer oil catch fire is known as fire point of transformer oil.

According to Indian standard the fire point of transformer oil 25% more than the flash point of transformer oil.

5.High pour point: The minimum temperature at which oil remains in liquid condition is know pour point of oil.

If the pour point of transformer oil will low, Then in winter or hilly area the maximum possibility of freezing the transformer oil.This effects the heat transferring of transformer by transformer oil.

So, the pour point of transformer oil should be -10°C (according to Indian standard).

6.No chemical impurities: The transformer oil should be free from chemical impurities.Because due to presence of chemical impurities it forms sludge that settle down in bottom of the transformer body.The transformer oil should be chemically inert.

7.Moisture less: It should be free from moisture.Because due to presence of moisture the insulating property of oil decrease and it also start the rusting of transformer body.It also effect the insulation of transformer winding.

8.Low viscosity: The transformer oil should have low viscosity.Due to low viscosity of oil it flow easily in transformer body, that is very effective for transformer cooling.

9.Free from dirt and dust: It should be free from dirt and dust.Due to presence of dirt and dust viscosity of transformer oil increases and it effects the heat transferring of transformer by transfer oil and also due to presence of dirt and dust in transformer oil sludge formation in transformer takes place.

10.Suitable permittivity: The permittivity value show the insulating permittivity of material, means higher the value of permittivity higher the insulating property of material and vice versa.So, the transformer oil should have suitable value of permittivity.

The permittivity of transformer oil should be 2.1 to 2.2.

DETERIORATION OF INSULATING OIL:

The decreases of dielectric strength of transformer oil is known as deterioration of transformer oil.

OR

When the standard value of transformer oil decrease, then it is known as deterioration of transformer oil.

The deterioration of transformer oil takes place due to following reasons:

1.Physical Deterioration: When dust, dirt and water mix with oil, then it is known as physical deterioration.The reason of physical deterioration is given below:

• The tank of oil remains open.
• The oil drum does not close properly.
• The installation of electric equipment near the moisture.
• The storage of oil is not proper.

2.Chemical Deterioration: The oxidization of oil is known as chemical deterioration.The reason of chemical deterioration of transformer oil is given below:

• Over load condition of transformer.
• Earth fault at transformer
• Short circuiting fault at transformer.

→When the hot oil comes in contact with water and oxygen, then oxidation of oil takes place.

3.Gaseous Deterioration: When the temperature of oil increase it vapourizes.This is known as gaseous deterioration of oil.Due to this flash point of oil decrease and oil can catch fire easily.

PRECAUTION AT A TIME OF TAKING OIL SAMPLE:

The precaution at a time of taking oil sample is given below:

• The oil sample should be taken from drain cock, that is situated bottom of the transformer oil tank. 

  

  Drain coke

• Drain coke should be clean by clean and dry cloth before taking oil sample.
• The sample of oil should be taken by the transformer when the transformer is on load condition.
• The oil sample should be taken in glass tube or bottle.The sample should not be taken in metal, rubber or plastic tube.
• The glass tube should be clean and dry.
• After taking sample, the oil filled bottle or tube should be covered properly.
• The cover of glass tube or bottle should not be made of rubber.
• The oil sample should be taken in sunny day.

→After taking sample, marking is should be done on oil filled bottle or tube with date and time.

Conclusion: The final conclusion is that transformer oil play a important role in transformer functioning.If we keep the above point regarding transformer oil in mind, then life of transformer increase and it works properly for a long time.

Important links:

What is transformer?Ratio of transformer?Different term in rating of transformer?

Different types of transformer?