Transformer oil viscosity refers to the oil’s resistance to flow and influences the oil’s heat transfer while flowing in small and large transformers. Viscosity is thus an important parameter while choosing the right transformer oil with required dielectric and coolant attributes. It is inevitable to monitor viscosity lest the transformer machinery would fail to protect components when crossing the recommended range.

Factors that affect transformer oil viscosity

The density of transformer oil which in turn is affected by its chemical composition, influences kinematic viscosity and ratio of dynamic viscosity of the oil. Dynamic viscosity is internal resistance to force and kinematic viscosity is internal resistance to flow.

Kinematic viscosity increases when used for longer periods and decreases when the oil is purified. Its value is directly proportional to the aging of transformer oil.

Benefits of low viscosity

When the viscosity is low the speed of circulation is high and provides higher heat dissipation and encourages heat exchange between the surface of the winding and the oil. Low viscosity oils allow the transformer apparatus to be smaller in size, use less amount of oil and operate at low temperature. It also resists deformation which occurs due to shear stress or tensile stress.

Such low viscosity optimizes cooling attributes of the transformer in instances where sludge clogs insulated windings and hampers heat exchange. Low heat exchange is compensated by low viscosity which in turn enhances the oil flow speed and gives a better heat dissipation.

Low viscosity also allows low cooling surface of radiator which reduces manufacturing cost of transformer and supports compact designs. Low viscosity also does not demand more oil for cooling purposes.

Viscosity and transformer oil filtration

Viscosity supports the speed in which the oil is pushed through a filter and enhances removal of contaminants. If the oil has high viscosity, the flow rate must be decreased.

Sludge accumulated in the transformer surface hampers oil circulation and the oil’s dielectric strength. The oil which is thus aged, is purified by removing sludge and moisture and maintaining the acidic degree. Interestingly, adsorbent materials like activated bauxite, carbonated calcium phosphate, chitosan polysaccharide and kaolin clay are gaining popularity for their efficiency in oil purification and removal of pollutants.

Characteristics of ideal transformer oil

Besides low viscosity, good transformer oil must possess high dielectric breakdown, absence of materials which may corrode metallic parts, zero moisture and no polar ionic contaminants, low levels of pour point and flash points.

Hering-The game changer in transformer oil filtration

Hering’s century plus old expertise in transformer maintenance coupled with undeterred focus in quality, retains their leadership in the industry. Hering’s EOK oil purification product line is supported by impeccable German technology with which accentuates the transformer’s capacity.

Besides removing moisture and enabling degasification, EOK series also eliminates volatile acids and enhances insulation. Hering is aware that increased voltages and accumulated stress could be harsh on the transformer and hence offers products in three series namely EOK Basic, EOK Standard and EOK Professional.

Thereby, customers can seek products based on requirements such as simple products for new transformers, onsite transformer service and repair and high end products with high flexibility and short cleaning times.