• What is Transformar oil :-
Transformer oil also known as insulating oil is a special type of
oil which has excellent electrical insulating properties and is
stable at high temperatures. Transformer oil is used in oil-filled
electrical power transformers to insulate, stop arcing and
corona discharge, and to dissipate the heat of the transformer
i.e. act as a coolant.
Transformer oil is also used to preserve the transformer’s core
and windings – as these are fully immersed inside the oil.
Another important property of the insulating oil is its ability to
prevent oxidation of the cellulose-made paper insulation. The
transformer oil acts as a barrier between the atmospheric
oxygen and the cellulose – avoiding direct contact and hence
minimizing oxidation. The level of transformer oil is typically
measured using a MOG Magnetic Oil level Guage.
• Types of Transformar oil
There are two types of oils used at present which are-
1)Paraffinic oil
2)Naphthenic oil
Transformer-oil-evr-power
1)Paraffinic oil
It is a mineral insulating oil derived from special crudes and
contains a substantial amount of n-paraffin. Paraffin oil has less
oxidation and has a boiling point of about 530°C. Due to high wax
content, the pour point is high compared to naphthenic oil.
Oxidation products are insoluble within the oil.
2)Naphthenic oil
It is a mineral insulating oil derived from particular crudes which
contain very low n-paraffin. Naphthenic oil has a boiling point of
about approximately 425°C. This oil is comparatively more
readily corroded than paraffinic oil. Due to less wax content, the
pour point is less compared to paraffinic oil. The oxidation
products are soluble within the oil. The paraffin-based crudes
generate an unsolvable sludge due to corrosion to increase
viscosity. Therefore it will reduce overheating, service life and
heat transfer. At relatively fewer temperatures like -40°C,
Naphthenic oils include aromatic components.
• Transformer Oil and its Uses:-
Transformer oil aka insulating oil is a special type of oil that is
stable at high temperatures and has excellent electrical
insulation. Transformer oil is basically used for two purposes –
as an insulating material and a cooling agent.
1. Insulating material :-
Transformer oil plays as an insulator and resists high voltage
because it includes high dielectric strength.
2. Coolant :-
The transformer coils can be designed with copper that carries
a high current so that the coils become hot. Since the coil is an
excellent heat conductor, transformer oil can be used to reduce
the temperature of the copper coil preventing it from burning.
• Properties of Transformer Oil:-
There are certain properties to meet for an oil to be used as
transformer oil. They are listed below:
• High specific resistance to get high insulation resistance.
• High specific heat capacity for better heat conductivity.
• High firing point to avoid catching fire easily.
• Low viscosity offers less resistance to the conventional
flow of oil thereby not affecting the cooling of a
transformer.
• Should not absorb moisture easily
• The electric, chemical and physical properties are
discussed below.
1. Electrical Property:-
• Dielectric strength– It is also known as breakdown
voltage(BDV). It is measured by observing what voltage,
sparking strands between two electrodes are immersed in
the oil, separated by a specific gap. If the value of BDV is
low, it indicates the presence of moisture content and
conducting substances. The minimum BDV or dielectric
strength of the transformer at which the oil can be safely
used is 30 KV.
• Specific oil resistance– It is a measure of DC resistance
between two opposite sides of a one-centimetre cube
block of oil. The resistivity of oil decreases with an increase
in temperature. The unit of specific oil resistance is ohm-
cm. The minimum standard specific resistance of
transformer oil at 90ºC is 35 × 1012 ohm-cm, and at 27ºC, it
is 1500 × 1012 ohm-cm.
• Dissipation factor of dielectric or tan delta- It is also known
as the loss factor or tan delta of transformer oil. Leakage
current will flow when insulating material is placed
between the live part and the grounded part of electrical
equipment. The insulation current ideally leads the voltage
by 90º. The voltage is led by the current through the
insulator with an angle a little bit shorter than 90º since no
insulating material is dielectric in nature. The transformer
oil’s dissipation factor of dielectric or tan delta is the
tangent of the angle by which it is short of 90º.
2 Chemical propertie:-
• Water content- Water content in transformer oil
unfavourably affects the dielectric properties of the
oil, hence it is not wanted. The allowed water content
in an oil is up to 50 parts per million.
• Acidity- The acidity test should be done to check the
acidic constituents of contaminants. It is a harmful
property. The water content in the oil becomes soluble
in the oil if the oil becomes acidic. The acidity of oil is
expressed in mg of KOH required to neutralize the acid
present in a gram of the oi
3)Physical Property
Flashpoint- It is the temperature at which the oil gives
enough vapour to produce a flammable mixture with air.
Pour point- Pour point is the minimum temperature at
which the oil starts flowing under standard test
conditions
