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Power transformers convert one voltage to another without changing frequency. The main parameter of transformer is transformation ratio, i.e. the ratio between primary and secondary coil voltages or the number of turns in the windings. To change transformation ratio, a tap changer is used, which changes the number of turns engaged at a given moment. Such devices allow keeping nominal voltage in the coils, if the primary or secondary voltage deviates from the setting. Tap changers operate with the transformer under load.

Tap changer oil system

There are two design types of tap changers depending on the oil system features. In the first case, the contactor of the changer is located in a separate tank on a insulator, while in the second case, the assembly is submerged, when the device is installed either inside the transformer tank or in a separate tank. The oil functions as an arc extinguisher; arcing may occur when the contactor is engaged.

For normal tap changer operation the temperature of the upper oil layers must not drop below -20 ⁰С. If the tank is separate, a special heating system is used to maintain the required oil temperature.

Frequent arcs degrade the oil’s quality. Heating of contactors, which occurs when transit resistance increases, further aggravates the problem. For best performance of the tap changer oil, its dielectric strength must be at least 30-40 kV with moisture content below 0.003%. Other tap changer oil parameters (color, acidity, carbon content) are of less importance and do not influence usability of the liquid in the contactor tank. Moisture content and dielectric strength are measured in oil samples taken every 5000 switches, but at least once a year.

The level of oil in the tank can be seen in the oil indicator. If the level is not maintained, arc burning time increases significantly, which should be avoided.

When selecting tap changer oil, viscosity must also be considered. If the oi lis too thick, the contactor must overcome higher mechanical resistance during switching, which may lead to failure in the long run.

Tap changer oil service life extension

If the analysis indicates that at least one of the parameters is out of specifications (moisture content or dielectric strength), the oil in the tap changer tank must be changed. However, frequent oil changes is not viable economically, which makes oil processing to dehydrate it and increase dielectric strength for oil reuse a reasonable alternative. This task is handled well by GlobeCore CMM-0.6 unit, which performs degassing and dehydration of tap changer oil with the processing rate of 600 liters per hour. This capacity is quite sufficient for servicing of the oil system.

The СММ-0.6 offers the following advantages:

• increasing dielectric strength to 60 kV;
• reduction of moisture content to below 10 ppm;
• a special system to prevent foaming, which is highly probable when processing oil with high moisture content;
• oil leak sensor. If a leak occurs, the unit automatically stops and notifies the operator;
• silent operation;
• powered by a regular power socket.

Mineral oils. Industrial oil, turbine oil, transformer oil and compressor oils are used in difficult conditions of high temperatures, exposure to air, mechanical contamination, contamination with water etc. Over time, these oils lose their performance properties and need to be replaced or regenerated.

As for other petroleum products, for example, diesel fuel may lose its properties in long storage storage under exposure to sunlight, moisture, air and dust. All mineral oils change their color with time.

Based on the current market demand for oil restoration equipment, GlobeCore developed a universal UVR-450/16 unit  for purification, clarification and regeneration of mineral oils and diesel fuels. This equipment fully restores the properties of petroleum products. The recovered oils will not darken and may be used for its purpose, saving money.

The UVR-450/16 unit has the following advantages:

• Manufactured in three versions: general purpose industrial frame, general purpose industrial container, fire and explosion proof;
• Easy switching from one oil to another without structural reconfiguration;
• Compact size;
• Manual or automatic modes;
• Does not require special placement.

The processing rate of UVR-450/16 in regeneration mode varies depending on the type of processed oil. For example, the processing rate of transformer oil is 0.3 m3/h, that of diesel fuel is 0.8 m3/h. Oil loss does not exceed 1.6% of the initial volume.

When using the UVR-0.1 oil cleaning and regeneration unit, the most frequent questions are the average amount of sorbent used and the amount of oil processed by this sorbent.

The UVR units for cleaning and regeneration of oil use a combination of thermal vacuum filtration with a special sorbent

The main feature of this equipment is the ability to work with various types of oil: transformer, turbine and industrial oils, diesel and heating oil, gas condensate, kerosene, etc.

It is important to understand that each of these oil products has different physical and chemical properties, and the amount of absorber used for regeneration may be different in each case. In general, the sorbent consumption is 3-17% of oil weight and 1-7% of fuel weight.

The UVR-120 unit is loaded with 120 kg of sorbent and it is possible to calculate the amount of oil cleaned with one load. With 120 kg it is possible to clean 700-4000 liters, which corresponds to 0.7 – 4 m3.

The consumption of absorber also depends on the degree of oil pollution and its acidity. The dirtier the oil and the more is its acid number, the greater amount of absorber is required to achieve the desired result.

Today, the problem of waste oil is quite acute and requires effective methods and approaches to its solution.  To understand the full extent of the problem, it is enough to look at only one fact: the amount of waste oil drained into water bodies and soil significantly exceeds the amount of the same substances entering the environment in case of accidents.  The financial aspect is equally important.  The high cost of lubricants makes their regeneration (at least partially) a reasonable and feasible solution.  Purification and regeneration technologies can significantly extend the service life of petroleum oils.  For example, transmission oil is recovered and sold through trading networks, and then poured back into gearboxes.  There is also the option of converting them into fuel oil.

The origin of waste oil also has a huge impact on the selection of its disposal method.  For example, emulsions for rolled aluminum are purified directly at steel mills and are re-used there for their intended purpose.

In general, the methods of waste oil disposal can be divided into several groups:

• Extending waste oil service life directly in the place of use;
• Partial recovery of lost performance with the extension of oil service life;
• Using waste oil as a part in the process of preparation of new marketable products in refineries;
• Regeneration of waste oil.  The advantage of this method is that it can be repeated many times over. Experts note that regeneration is an ideal way of restoration of the original state of waste oil.  This makes it possible to achieve maximum economy of oil resources.
• Dehydration.  This recycling method involves removal of water from waste oil, followed by its further use as a heat carrier.  In fact, it’s burning of dewatered waste oil for heating of industrial and residential premises.  Since this type of recycling is a one time deal, it is not considered very efficient.  But the obvious advantage of this approach is the opportunity to generate low cost electricity and heat;
• Thermal cracking.  Application of this process does not enable restoration of waste oil. In this case, the waste product is converted into fuel which resembles diesel oil.  The area of application of this material mainly comes down to domestic purposes, including heating.  Cracking is also considered a good recycling option because it yields 85% of the original amount of raw materials;
• Physico-chemical recycling methods.  This group of methods includes a variety of techniques.  We’ll consider the most common ones.

Coagulation is the precipitation of various impurities dissolved in the oil.  To ensure the binding of waste particles, special coagulants are used.  This approach requires strict maintenance of a certain temperature, reagent dosage, as well as heavy oil mixing.  In general, it takes about half an hour for the impurities to settle, and then the oil product undergoes treatment by sedimentation, filtration or separation.

Adsorption treatment is based on the ability of some substances to attract contaminants and then absorb them in their granules.  Natural minerals (clay, bauxites, zeolites) usually act as adsorbents.  It is possible to use substances specifically synthesized by scientists for this purpose: silumin, silica gel, aluminum oxide etc.

Ion-exchange treatment is the removal of foreign impurities that are prone to decomposition into ions in solution.  For this process, oil is mixed with ionite particles, then substitution of ions in the crystal lattice occurs: “pure” ions take the place of “dirty” ones.  The used ion exchangers naturally lose their original properties; therefore they must be restored by solvent treatment, drying and activation with caustic soda solution.  Ion-exchange treatment shows good results in removing acidic components, but it is unable remove resins.

Selective treatment helps clean waste oil from nitrites, oxides, sulfur compounds, thus reducing its viscosity-temperature behavior.  This method of processing oil which has lost its operational properties requires the use of a variety of liquid synthetic solvents.

GlobeCore is one of the leading manufacturers and suppliers of equipment for purification and recovery of various petroleum products, ranging from transformer oil to heating oil.  GlobeCore uses the latest technology to restore the operating parameters of waste oils, which makes it possible to re-use it for its intended purpose.  To meet the needs of its customers, GlobeCore is ready to offer both stock and customized equipment.

None of the literature on diesel fuel disproves the benefits of filtration.  This process helps to get rid of dust and dirt particles that can penetrate into supply system through nozzles.  It is caused by periodic opening and closing of the fuel tank.  When channels and spray nozzle holes are clogged, insufficient amount of fuel is supplied to the combustion chamber, resulting in reduced engine power.

Purified fuel burns out more efficiently, emits less toxic gases, increases engine power and reduces fuel consumption.

Filtering is necessary to protect friction surfaces and other fuel system components from solid contaminants. Filters that are composed of a housing and a filter element are typically used for this purpose.  Filter elements can be made of synthetic fibers, cellulose or special paper.  Various parameters can be used to describe the effectiveness of a filter.  One of the most significant parameters is the maximum particle diameter that can pass through the filter.  The so-called filtration beta-rate is also used in practice.  It involves estimation of the ratio of certain size particles amount in the fuel upstream of the filter to the amount of the particles downstream of the filter.  The higher the beta-rate, the better the filter efficiency.  The challenge is to select the correct filter to remove impurities of a certain size.  Otherwise the filter will not function.  Currently you can find filters that can remove not only solid particles but also water contained in fuel.

Such devices require constant attention because water overflow can cause the device to lock, as a result of which contaminated fuel will flow past the filter element.

Fuel separation

Separation is, in fact, a form of filtering.  It is used when fuel is contaminated to such an extent that an ordinary filter cannot cope.  The main advantage of separators is the ability to remove impurities, even in high concentration.  There are models that can remove both solid particles and water from fuel. Separators are combined devices by the mode of functioning:  They combine mechanical and chemical principle of operation.  First, the fuel is freed from solids and water in a centrifuge; they are collected at the bottom of the bowl and only then filtered through paper, impregnated with a special substance. Such substances possess the ability to bind water emulsion, which 20-25 times exceeds their own weight.

Separators are a good solution if the fuel is heavily polluted, but they also require very complex maintenance.

Additives

Use of additives is a fundamentally different approach to the improvement of diesel fuel.  Its essence is to improve only some individual characteristics of fuel by addition of special chemicals.  When selecting an additive, one should always remember that even the most high-quality product may still have some negative properties.  That is why the attitude of drivers and managers of large fleets to additives is not unambiguous.

The most useful and effective additive formulations help prevent the proliferation of bacteria and micro-algae in fuel.  They are suitable for use when fuel is stored in a tank for a long time. Bear in mind these additives do not improve indicators such as viscosity, cetane number and lubricity.

Anti-wear additives are used to prolong the life of fuel system, improving the lubrication properties of diesel fuel. These are used with low sulfur diesel fuel.

There is also a group of additives to increase the cetane number which improves engine starting characteristics at low temperatures, as well as vehicle performance.  In general, additives that increase the cetane number do not affect any other properties of fuel, except for lubricity.

At high lubricity the use of such additives is not so critical, but with medium or low lubricity it can cause accelerated wear of engine components, and in some cases nozzle damage.

Depressors are designed to improve the low temperature properties of diesel fuel.  Their effect is based on reducing paraffin solidification temperature, thereby improving the filter point of fuel.  When selecting this type of additives, you should be aware that it is not capable of preventing stratification of fuels during storage at low temperatures.

Other additives are mixed with fuel together with depressants to form very fine paraffin crystals, which do not precipitate, but are uniformly distributed throughout the volume of the fuel.

Detergent additives are the most commonly used.  Their popularity is due to their ability to remove various deposits or impurities.  Older engines have sludge and varnish deposits on the walls, which adversely affect fuel combustion and increases toxic emissions.  Detergent additives help to avoid these effects and slightly reduce the consumption of diesel fuel.

Filter + additives = is peaceful coexistence possible?

If a filter is designed to operate with certain types of fuel, using additives does not guarantee fuel properties required for effective filtering.  Sometimes additives are separated from fuel during purification, which makes the use of such additives meaningless.  Therefore, the combined use of additives and filters must be approached wisely and carefully: it can have an unexpected harmful effect.

Restoring marketable condition of the fuel

Companies involved in the sale of petroleum products pay much attention to marketable appearance of diesel fuel.  As a result of long-term storage and exposure to air, diesel fuel can be oxidized and darken, which is not a good thing for sales.

When dealing with medium and large volumes of fuel, use the UVR-type plants by GlobeCore.  They can clarify dark petroleum products, remove odor, water and mechanical impurities.  The plant allows to remove hydrogen sulfide compounds, reduce sulfur concentration, lower wax content and remove unsaturated hydrocarbons.  After purification and clarification the fuel does not oxidize or darken again.

UVR-type plants have the following advantages:

• Mobility.  The equipment can be easily loaded onto a van and moved directly to the storage of oil products for processing;
• automatic or semi-automatic operation capability, minimizing human involvement in the purification process;
• Versatility. The UVR-type plants can be used to clean and restore not only diesel fuel, but gasoline, kerosene, heating oil, light mineral oil etc.

The UVR-L laboratory regeneration unit is designed to purify fuels and regenerate oils with viscosity below 70 cSt at 20ºС.

This equipment is very versatile, capable to treat practically any type of oil products including transformer, industrial and turbine oils, as well as fuel oils, gas condensate and diesel fuels.

The laboratory version of this product can be used by either research facilities or companies which already own larger UVR units.

The potential scope of UVR-L functions is:

• to study efficiency of various adsorbents for purification of oil products;
• to optimize purification of waste oil by larger UVR plants;
• to evaluate the efficiency and the rate of regeneration when shanging initial conditions, to access sorbent consumption depending on the type of oil product.

UVR-L design

The laboratory unit for purification of fuels and regeneration of oil consists of a regeneration pod, a frame, a vacuum chamber, a vacuum pump, a control cabinet, a coalescer dryer and piping.

Operation Principle

Operation principle of the UVR-L unit is based on heating, vacuum treatment and regenerating properties of the adsorbent.

The required amount of adsorbent is filled into regeneration pod. Oil flows through the adsorbent and then fills the vacuum chamber. The vacuum pump creates the required negative pressure. When the regeneration process is completed, a special valve opens and recovered oil is drained from the vacuum chamber.

Structurally, the regeneration pod is a tank, half filled with the adsorbent. There is a lid in the upper part. It is used for oil or adsorbent input.

The lower part of the regeneration pod contains a rubber hose filled with adsorbent and the lower lid, through which vacuum is applied, saturated sorbent is removed and oil is sampled.

The upper surface of the module is equipped with a heater strip and is insulated.

Specifications of the UVR-L unit

#	Parameter	Value
1	Regeneration capacity, l/hour:
	– transformer oils	3-5
	– turbine oils	3-5
	– industrial oils	2-4
	– dark fuel oil	4-10
	– dark diesel fuel	4-10
	– dark gas condensate	6-11
2	Consumption of regenerating powder, % of oil weight:
	– transformer oils	3-17
	– turbine oils	3-17
	– industrial oils	3-17
	– dark fuel oil	5-20
	– dark diesel fuel	1-7
	– dark gas condensate	1-3
3	Regenerating powder load, kg	3
4	Loss of oil in % of initial oil volume:
	– transformer oils	3-5
	– turbine oils	3-5
	– industrial oils	3-5
	– dark fuel oil	3-5
	– dark diesel fuel	2-4
	– dark gas condensate	1-3
5	Heater power consumption, kW	0.16
6	Total power consumption, kW	1.0
7	Voltage of 3–phase of AC, 50 Hz, V	380
8	Overall dimensions, mm:	1,0
	– length	500
	– width	550
	– height	750
10	Weight, kg max	65

Advantages of the UVR-L unit:

• small size;
• simple transportation;
• can be connected to regular power sockets;
• oil samples can be treated directly on site;
• noiseless operation.