Tag Archives: oil degassing

Classification of New Transformer Insulating Oil Testing

The conditions in which insulating oil is used in transformers, switches, and other high voltage equipment are rather demanding on the performance characteristics of the insulating oil.  During the service life of the oil, it is heated by currents, contaminated by particles of solid insulation and chemical reactions with the internal surfaces of the equipment.  Each of these separately and together significantly accelerate the aging of transformer oil and can make the oil harmful to the equipment.  This is especially true with regards to the transformer insulating paper.

A sample of transformer oil is taken from the lower part of the transformer oil tank after rinsing the drain opening with oil.  The sampling vessel must be clean and very dry or the testing results will not reflect the true condition of the oil being tested.

Local and international standards define certain parameters by which the oil must comply.  Oil analysis and testing should be performed directly before placing oil into the electric power equipment.

New transformer oil is also tested before being placed into transformers.  The purity and quality guaranteed by the manufacturer of the oil does not prevent water, air and solid particles from entering the oil during handing and storage.  You cannot assume that the new oil is free from contaminates and moisture.  The oil must be properly analyzed immediately prior to use to ensure the proper operation of your electrical equipment

Before a transformer is energized, the oil in the transformer must be briefly tested for minimum dielectric strength levels, solid particulate matter, acidity and flashpoint.  If different brands of oil are used in the transformer, the final blend must be tested for stability.  The blended oil fill should not be inferior in stability to any of the separate oils with the lowest stability value.

Used oil must be tested according to standards that have been set for the operation of industrial equipment that it will be used in.

Before testing, the vessel, containing the oil sample, is inverted and turned slowly around several times to eliminate air bubbles from the oil sample.  A ceramic oil test vessel with electrodes is filled three times.  Oil is poured on the walls of the vessel in a thin stream so as to prevent formation of air bubbles.  The level of oil in the vessel must be at least 15 mm higher than the top of the electrodes.

Transformer oil is allowed to settle in the vessel for 15-20 minutes for air bubble removal.  The voltage is then gradually increased at the rate of 1 – 2 kV per second.  After a breakthrough is achieved (spark between the electrodes), voltage is recorded and then dropped to zero.  Six tests are performed and the average of the last five tests is taken.  The first breakthrough is not averaged in since it was only performed as a guide.

After each breakthrough, carbon particles are removed from the space between the electrodes by clean glass or metal rods.  The liquid is then allowed to settle for 10 minutes before performing the next test.

The transformer oil sampling process will vary from facility to facility depending on the equipment used and purity requirements of the equipment and oil being tested.

At any rate, a timely oil analysis program may well prevent significant costs and losses for your company.

Transformer Oil Storage Tanks

In power transformers and in electric equipment in general, oil is used to insulate and to cool.  The use of various types of oil for power systems is governed by internationally recognized standards.  The purpose of the uniform standards is to keep electric power equipment and systems in good working condition.  Of course, this depends on the performance characteristics and general condition of the transformer insulating oil.

Any business that uses oil must be concerned with the issue of oil storage and disposal.  This is especially important for the energy sector and the electric power generating and transmission industry.

Transformer insulating oil may come from the factory or substation in more than one condition.  Even when the oil is fresh from the manufacturer, it is possible that undesirable amounts of moisture and gases accumulated in the oil during transportation.  Transformer oil delivered from the manufacturer and purified to comply with the performance standards is usually stored in liquid storage tanks at maintenance facilities.  Regardless of the condition of the oil, whether it is new or used, it must be stored in a safe and leak proof container.

For the purposes of fire safety, the manufacturer must strictly adhere to national safety and fire prevention standards.  The actual method of storage however, and the availability of specially equipped buildings, tanks, and service equipment can vary greatly depending on location, climate and country.

A wide range of different oil storage tanks can be found in the local and international markets.  There are soft tanks that can drain and store oil more quickly reducing transformer servicing and possible downtime.  But, these types of tanks are better suited for transporting oil to interim storage facilities.

For actual storage of liquids, the most widely used tanks are vertical cylindrical tanks that are equipped with leveling quality controls, agitation systems, temperature sensors and built-in maintenance systems.

A vertical insulated tank is made of steel with heated circulation pipes below the surface.  For tank maintenance and servicing, a ladder is mounted on the tank with a protective rail along the top. Temperature is monitored by a thermistor installed in the bottom of the tank that displays the temperature on the tank’s control panel.  The heat exchange system is made of an array of pipes and insulation jackets.

Proper oil storage systems should be designed to keep the oil in good condition and preserve the oil’s performance characteristics.   Proper stored oil maintenance will help in eliminating the costs associated with additional purification and regeneration due to premature aging of the oil while being stored before use in your electric power equipment.


Methods of Transformer Oil Purification

Transformer oil serves to insulate the energized parts and components of electric power transformers and also acts as a heat transfer medium.  Additionally, it  protects the solid insulation from damaging moisture.  Besides transformers, insulting oil is used in switches, high voltage capacitors and power cables.  In switches, the oil acts as an arc extinguisher preventing fires and possible explosions.

Over the course of the transformer’s service life, that may span many years of operation, the insulting oil will accumulate various contaminants that adversely affect the oil’s performance characteristics.  Once the insulating oil’s performance characteristics have been diminished, the transformer’s solid insulation will be in greater risk of failure.  In order to restore them, the oil must be purified of foreign substances and contaminates (water, gases and solid particles).  Today, we’d like to look into the methods of transformer oil purification.  Different methods of purification can be used depending on the substance(s) that need to be removed from the oil.

Centrifugal purification is a method for water removal.  It separates unwanted materials, including water and moisture, under centrifugal force.  The main advantage of this method is the relatively high rate of water removal.  There are however, several drawbacks to this method that include; (1) a low degree of overall purification of the oil; and (2) complexity and the necessity for constant presence of service personnel supervising the process.

Another method for water removal is adsorption purification.  The biggest advantage of this method is its simplicity.  The drawbacks are: (1)  the dependency of the purification rate on the type of sorbent used; (2) the need to dispose of used sorbent and the potential environmental risks; and (3) the high quality requirement to input oil and the low rate of processing capacity.

The difference between he boiling point of water and oil is the essence of thermovacuum drying. The oil to be purified goes into a special chamber with low pressure.  In such conditions water evaporates at room temperatures.  The method allows for high efficiency purification.  It is very reliable and requires no complex adjustments.  The main drawback is the relatively low rate of water removal.

The above methods may also be used for removal of gases, solids and acids from transformer insulating oil,  e.g. thermovacuum purification is also a good method for removing unwanted gasses.  Centrifugal purification can also remove solid particles.  Single and multiple use filters with a high degree of purification are also used for the same purpose. Such filters must be replaced from time to time.  Acidity of the oil is decreased by the adsorption method and has become a highly desirable process for a more complete maintenance service for your electric power transformers.

The most modern and cost effective method for performing transformer maintenance is the industry leading GlobeCore Process which uses a Fuller’s Earth sorbent filtering system.  The GlobeCore Process uses the adsorption method to not only purify the transformer insulating oil, but to completely “regenerate” the oil by removing the contaminates and moisture from the entire transformer and not just the oil.

Unlike the older adsorption methods, the GlobeCore Process has eliminated the need to dispose of spent sorbent materials through the development and use of an automatic sorbent reactivation system.  This technological breakthrough has now made the GlobeCore Process of oil purification and regeneration the most efficient and cost effective transformer maintenance system in the world.

It’s time to get with the Process.  The GlobeCore Process!

Transformer oil degassing as a part of comprehensive purification system

While operating expensive power equipment, such as compressors, turbines, hydraulic presses, heat exchangers and power transformers, unforeseen malfunctions will happen. In rare cases failures are caused by overvoltage of the grid or human mistake, since operation of power equipment is a safety issue. Equipment downtime, failures and malfunctions are most often caused by the problems of internal components or insulation. Oil of various kinds are used for servicing of different industrial machinery. As a result of contamination by solid particles or moisture and air, as well as high temperatures, equipment may fail which may stop the whole manufacturing process.

Comprehensive oil purification systems are becoming more used recently; if before industrial oil service life could be extended by separate degassing, drying and filtration systems, with totally spent oil being disposed of, now operation of comprehensive oil purification and regeneration systems becomes preferable.

Removing gas, water emulsions, and harmful oxidation products form the oil extends the service life of the expensive insulation material and ensures the power equipment is adequately protected.

Comparison of purification and regeneration plants made by different companies yields significant differences.

Most of the modern manufacturers emphasize removal of water in all forms and solid particles from turbine, compressor, hydraulic and industrial water. Removal of air, gas and volatile hydrocarbons is a secondary function.

Despite the normal production levels of such systems and their seeming versatility, there are other options with more worth.

The whole range of GlobeCore degassing, purification and regeneration of oil by GlobeCore is focused on all processes at the same time, in one pass and with reactivation of purifying media.

One full regeneration cycle of oil coming directly from power equipment allows to remove gas, water and particulate matter form the oil; it is also possible to use adsorption media to regenerate the oil entirely. GlobeCore’s sorbents offer additional savings due to the reactivation capability.

A complete GlobeCore plant for degassing, filtration and regeneration of oil and other liquids is an optimal choice of service equipment for control of production process and ruling out any unpleasant surprises.

What is better “drought” or “rainy season” – the percentage of moisture in dry transformer oil

Transformer oil aging results in degradation of its properties. The aging process is accelerated by influence of water, air or contaminants. Moisture and air cause the oil to oxidize, which lowers it’s dielectric strength, causes sludge deposits on transformer internal insulation and damages the insulation by the acidic products of oil decay.

Water may be present in transformer oil in various states: solved, emulsified or free. Even new oil contains solved water. Free water mostly accumulates in the lower parts of oil lines and in heat exchange devices. Water is solved in oil under the influence of high temperature. During operation water content in the oil increases, and may be extremely harmful for a transformer.

GlobeCore’s equipment allows removal of contaminants, including water, directly on energized transformers in compliance with the highest international standards.

Complete transformer oil filtration and regeneration systems are designed for full range of services to purify waste oil. The units are equipped with adsorbents for restoration of oil performance and improving its color.

According to international research, various sorbents may be used for drying of oil, as well as for retention of oil aging products. Some of the sorbent may be reactivated, which makes GlobeCore plants not only highly advanced by also very sensible in terms of return on investment.

The UVM type mobile oil plants are designed for the following operations:

  • Dehydration of oil for moisture content of no more than 10 ppm.
  • Degassing of oil to no more than 0.1% of gas content by volume.
  • Increase of dielectric strength to at least 70kV.
  • Drying of electric equipment with simultaneous oil purification.
  • Initial filling of dielectric oil into electric systems;
  • Nitrogenation of oil;
  • Vacuum evacuation of transformer and other electric systems.

GlobeCore’s plants significantly increase oil processing stability and consistency and improve oil performance.