Transformer Oil Viscosity

turbine oil filtration

Transformer oil is a product obtained from crude oil.  It is used as electrical insulation material, for heat dissipation and arc-extinguishing, as well as the medium protecting solid insulation from air and moisture.  As you can see, the list of tasks is rather large, which poses certain demands to the properties of transformer oil.  In this article, we would like to talk about viscosity.

What is transformer oil viscosity?

Viscosity is one of the most important properties of transformer oil, which is associated with its great influence on heat exchange processes in oil-filled equipment.

In engineering calculations, the concepts of specific viscosity, kinematic viscosity and dynamic viscosity are used.  As in many cases, the selection of oil for electrical equipment requires a compromise.  The thing is that high viscosity affects electrical properties in a good way, while low viscosity reduces the cooling capacity.  Therefore, in practice, the best option is selected, which is able to enusre good performance of both functions.

Since operating conditions of power transformers are quite severe and may be characterized by elevated temperatures, one should take into account the change in oil viscosity when heated.  Raise in temperature decreases its viscosity and vice versa.  Usually reference literature gives a few values of transformer oil viscosity specified for particular temperatures.  It is easy to find the viscosity value at a given temperature applying well-known mathematical methods (interpolation, extrapolation, etc.), even if it is not listed in the directory.  For example, the average value of transformer oil kinematic viscosity is (28-30)∙10-6 m2/s.

Measuring of transformer oil viscosity

Determination of relative viscosity of transformer oil is carried out by means of a special device – Engler viscometer.  It consists of brass and metal vessels, a calibrated tube, cork and register pins.

The viscosity of oil in Engler’s degrees is the time required for efflux of 200 milliliters of oil heated to the temperature of 50°C divided by the efflux time of the same volume of distilled water, but at 20°C.

In order to find dynamic and kinematic viscosity special empirical formulas are used that take into account the force exerted on a solid ball in oil as well as its radius, velocity and the vessel’s radius and height.  Kinematic viscosity is obtained by dividing the known dynamic viscosity by transformer oil density.  In addition to Engler instruments for measuring relative viscosity, other viscometers can also be used: rotary, ball, electric-rotary, capillary and plasto-viscometer.

Maintaining the desired viscosity of transformer oil

Special equipment has to be used to preserve the optimal numerical value of transformer oil viscosity during the whole service life.  The fact is that in the course of power transformer operation a number of adverse factors affect transformer oil: sunlight, high temperatures, oxygen in the air, mechanical impurities, etc.

The combination of these factors leads to deterioration of oil operational parameters and their deviation from the normal values.  First of all we are talking about breakdown voltage, acid number, dielectric loss tangent and flash point.  Viscosity is no exception too.

Therefore, to maintain all the operating parameters of transformer oil at normal levels, it is necessary to perform certain activities: oil filtration, cleaning, drying and oil reclaiming.

GlobeCore offers a wide range of equipment designed to deal with transformer oils. Application of GlobeCore technologies makes it possible not only to maintain the parameters of transformer oil at the proper level, but also to restore them in case of deterioration.

Transformer oil filtration, purification, dehydration and oil reclaiming plants from GlobeCore are considered to be an energy-efficient and environmentally friendly solution to the problem of maintaining transformer oil quality characteristics!  To ensure reliable operation of your oil-filled equipment, simply contact our specialists and use their help to choose a plant with the required performance.