Viscosity of transformer oil: kinematic and conditional. Big encyclopedia of oil and gas
6. The limitation of the validity period was removed according to protocol N 2-92 of the Interstate Council for Standardization, Metrology and Certification (IUS 2-93)
7. EDITION (June 2011) with Changes N 1, 2, 3, approved in March 1982, March 1985, March 1989 (IUS 7-82, 6-85, 6-88), Amendment (IUS 6-2005)
This standard applies to transformer oils of sulfuric acid and selective purification, produced from low-sulfur oils and used for filling transformers, oil circuit breakers and other high-voltage equipment as the main electrical insulating material.
1. STAMPS
1. STAMPS
The following brands of transformer oils are installed:
TK - without additive (produced by special orders for general technical purposes), it is not allowed to use for pouring transformers;
T-750 - with the addition of (0.4±0.1)% antioxidant additive 2.6 ditertiary butyl paracresol;
T-1500 - with the addition of at least 0.4% of the antioxidant additive 2.6 ditertiary butyl paracresol;
PT is a promising oil.
(Changed edition, Rev. N 1, 3).
2. TECHNICAL REQUIREMENTS
2.1. Transformer oils must be manufactured in accordance with the requirements of this standard, from raw materials and according to the technology used in the manufacture of oil samples that have passed tests with positive results and are approved for use in the prescribed manner.
2.2. In terms of physical and chemical parameters, transformer oils must comply with the requirements and standards specified in the table.
Name of indicator | Norm for the brand | Test method |
|||
TK OKP | T-750 OKP | T-1500 OKP | |||
1. Kinematic viscosity, m/s (cSt), not more than: | |||||
at 50 °C | |||||
at minus 30 °С | 1200 10(1200) | ||||
2. Acid number, mg KOH per 1 g of oil, no more | |||||
3. Flash point, determined in a closed crucible, °C, not below | |||||
Absence | |||||
6. Pour point, °C, not higher | |||||
7. Sodium sample, optical density, no more | |||||
10. Color on the CNT colorimeter, CNT units, no more | |||||
11. Stability against oxidation, not more than: | |||||
______________ Notes: 1. For transformer oil grade TK, produced from Emba oils and their mixture with Anastasyevskaya oil, when tested for stability against oxidation according to GOST 981, the mass of volatile low molecular weight acids is allowed 0.012 mg KOH per 1 g of oil, the acid number of oxidized oil is not more than 0, 5 mg KOH per 1 g of oil. |
|||||
(Revised edition, Rev. N 2, 3, Amendment).
3. SAFETY REQUIREMENTS
3.1. Transformer oils are low-hazard products and, according to the degree of impact on the human body, they belong to the 4th hazard class in accordance with GOST 12.1.007.
3.2. According to GOST 12.1.044, transformer oils are flammable liquids with a flash point of 135 °C.
3.3. The room in which work with oil is carried out must be equipped with supply and exhaust ventilation.
3.4. The maximum allowable concentration of vapors of hydrocarbon oils in the air of the working area is 300 mg / m in accordance with GOST 12.1.005.
3.5. When working with transformer oils, personal protective equipment must be used in accordance with the standard rules approved in the prescribed manner.
3.6. When oils catch fire, the following fire extinguishing agents are used: sprayed water, foam; with volumetric quenching - carbon dioxide, the composition of the SZhB, the composition is 3.5, steam.
Section 3. (Changed edition, Rev. N 3).
4. ACCEPTANCE RULES
4.1. Transformer oil is accepted in batches. A batch is considered to be any amount of oil produced during the technological process, homogeneous in terms of quality, accompanied by one quality document containing data in accordance with GOST 1510.
(Changed edition, Rev. N 3).
4.2. Sample size - according to GOST 2517.
4.3. Upon receipt of unsatisfactory test results for at least one of the indicators, repeated tests of a newly selected sample from the same sample are carried out.
The retest results apply to the entire lot.
(Changed edition, Rev. N 3).
5. TEST METHODS
5.1. Samples of transformer oils are taken according to GOST 2517.
For the combined sample, 3 dm of oil of each brand is taken.
(Changed edition, Rev. N 1).
5.2. A sodium sample for oils of the T-750 and T-1500 brands is determined in a 20 mm cuvette, for TK oil - in a 10 mm cuvette.
5.3. The transparency of transformer oils is determined in a glass test tube with a diameter of 30-40 mm. Oil at 5 °C should be transparent to transmitted light.
5.4. The sediment index and acid number for TK brand oil are determined according to GOST 981 under the following conditions:
temperature - 120 °С,
oxygen consumption - 200 cm / min,
the duration of oxidation in the determination of sediment and acid number - 14 hours.
The indicator of low molecular weight volatile acids is allowed to be determined under the following conditions:
temperature - 120 °С,
catalyst - balls with a diameter of (5 ± 1) mm, one of low-carbon steel, one of copper grade M0k or M1k according to GOST 859;
air consumption - 50 cm / min;
oxidation time - 6 hours.
The stability against oxidation of oils of grades T-750 and T-1500 is determined according to GOST 981 under the following conditions:
temperature for T-750 brand oil - 130 °C, for T-1500 brand oil - 135 °C,
catalyst - copper plate,
oxygen consumption - 50 cm / min,
The oxidation stability of a promising hydrocracking oil is determined according to GOST 981 under the following conditions:
temperature - 145 ° С,
catalyst - copper plate;
oxygen consumption - 50 cm/min;
oxidation time - 30 hours.
(Changed edition, Rev. N 1, 2, 3).
5.5. The dielectric loss tangent of transformer oils is determined without preparation or after preparation by one of the following methods:
a) 100 cm3 of oil is held for 30 minutes at 50°C at a residual pressure of 666.6 Pa (5 mm Hg) in a vessel with a free surface of 100 cm3;
b) the oil is kept in a crystallizer placed in a desiccator with calcined calcium chloride for at least 12 hours with a layer thickness of not more than 10 mm.
In case of disagreement arising from the assessment of product quality, oil preparation before determining the dielectric loss tangent is carried out according to subparagraph a.
To determine the dielectric loss tangent, electrodes made of stainless steel grade 12X18H9T or 12X18H10T according to GOST 5632 are used. In the manufacture of electrodes from copper according to GOST 859 and brass according to GOST 17711, the working surfaces of the electrodes must be coated with nickel, chromium or silver. The determination is carried out at an electric field strength of 1 kV/mm.
6. PACKAGING, LABELING, TRANSPORT AND STORAGE
6.1. Packaging, marking, transportation and storage of transformer oils - according to GOST 1510.
6.2. On the document certifying the quality of transformer oil grades T-750 and T-1500 of the highest category, and on the container, the State Quality Mark must be depicted.
7. MANUFACTURER WARRANTY
7.1. The manufacturer guarantees that the quality of transformer oil meets the requirements of this standard, subject to the conditions of transportation and storage.
7.2. Guaranteed shelf life of transformer oils is five years from the date of manufacture.
(Changed edition, Rev. N 2).
Electronic text of the document
prepared by Kodeks JSC and verified against:
official publication
Oil and oil products. Oils.
Specifications. Collection of GOSTs. -
M.: Standartinform, 2011
In the same connection is the experimental fact that with a decrease in the viscosity of transformer oil when it is heated, the absorption coefficient does not decrease (as it should be for low-amplitude waves), but increases.
As for the change in the viscosity of oils at low temperatures1, then, as follows from Table. 11, borrowed from the same work, a sharp increase in the viscosity of transformer oil is observed already at temperatures below minus 30 C, and for turbine oil at a temperature of minus 5 C.
For use in power transformers in the USSR, Sovtol-10 is mainly used, which is a mixture of 90% pentachlorobiphenyl and 10% trichlorobenzene, which has a viscosity close to that of transformer oil in the operating temperature range. However, in terms of its viscosity-temperature properties, Sovtol-10 is significantly inferior to hexol, which is a mixture of 20% pentachlorobiphenyl and 80% hexachlorobutadiene. Hex-sol does not freeze at temperatures up to - 60 C and is less affected by pollution.
Two series of experiments were carried out. The viscosity of the transformer oil was reduced by adding a solvent - kerosene - and dissolving natural gas in it.
The viscosity of transformer oil is strictly regulated. Transformer oil supplied to enterprises is thoroughly dried in special installations and filtered many times. The breakdown voltage of oil before pouring into the transformer must be at least 50 kV with a distance between two electrodes in a standard punch of 25 mm.
In most cases, dry transformer oil (GOST 982 - 56), which has good electrical insulating properties, is used for this purpose. The viscosity of transformer oil is low, as a result of which its convection and circulation provide good cooling of the equipment, which is especially important for devices with elements that heat up during operation. The oil also protects the equipment from atmospheric influences and from the harmful effects of a chemically aggressive environment.
The main advantage of transformer oil is its high insulating properties and the ability to protect the cooled path from corrosion. However, the viscosity of transformer oil is much higher than the viscosity of water. Therefore, in order to create an oil circulation that is commensurate in efficiency with the circulation of water, large pipeline diameters and a higher head are required. The oil pressure in the pipeline is limited to 3 - 4 kgf / cm2, because due to the good wettability of metal surfaces, at high pressures it is able to seep through minor leaks that almost always occur in pipeline joints.
In technical standards, the value of v20 is indicated as one of the parameters characterizing this oil, however, in Fig. Therefore, the viscosity of the purified transformer oil at 20 C will be determined approximately, using, for example, Gross's formula (I, 56).
| Heat dissipation efficiency. / - organosilicon liquid of high viscosity. 2 - transformer oil. 3, 4 and 5 - organofluorine liquids (C4P9 3M, CSF16O and C6F120. | Application of a refrigeration unit for transformer cooling. |
This can be especially valuable for power-limiting transformers that would otherwise be non-transportable. It should be noted that the viscosity of transformer oil increases with decreasing temperature, so the heat transfer coefficient from the windings to the oil will be lower than in conventional oil transformer systems.
If the stator cavity is filled with transformer oil, then during start-up in winter time it is necessary to create a minimum load or, if it is permissible, start in idle mode and continue to operate the electric motor in this mode to warm up the entire volume of oil to 15 - 20 C without supplying cooling liquids into the cooling system. This is necessary because the viscosity of transformer oil at low temperatures is high and its circulation throughout the circuit will be difficult, which can lead to local overheating and charring of the winding insulation even when the oil temperature at the measurement points has not yet reached the limit values. .
The operation of electric motors, the stator cavity of which is filled with transformer oil or water cooling is used to remove heat, in winter in open areas or in unheated rooms has a number of distinctive features. This is because at low temperatures the viscosity of transformer oil increases and water can freeze in the cooling system if proper precautions are not taken.
The decrease in viscosity at a given flash point is achieved by narrowing the fractional composition; the implementation of this measure is limited, since it reduces the oil yield. In recent years, abroad, there has been a tendency to reduce the viscosity of transformer oils, even with a slight decrease in the flash point.
The viscosity of transformer oil is an important physical parameter that determines the process of heat transfer of windings and magnetic cores in transformers and the arc-extinguishing capacity of circuit breakers. For good oil circulation in transformers, which improves the cooling of windings and magnetic cores, oils with low viscosity are needed. In turn, the oil, like other liquid dielectrics, the viscosity greatly increases with decreasing temperature. At a temperature of 20°C, the viscosity of transformer oil should be no more than 4.2°Oe and no more than 2°Oe at a temperature of 50°C.
To measure the relative viscosity - VU of the oil, an Engler viscometer is used, the scheme of which is shown in fig. 3. A brass vessel - 2 is placed inside a metal vessel 1 so that there is a space between them filled with water. Both vessels in the center have holes through which a calibrated tube is passed - 3
Diagram of the Engler viscometer.
with an inner hole diameter of 2-3 mm. This hole is closed with a stopper - 4. The brass vessel is filled with the test liquid along the index pins - 5. Simultaneous contact with oil of all three points is a sign of correct installation on the table, the inaccuracy of the installation is corrected by the set screws on the legs of the device. The outer vessel 1 serves as a water bath, from where the water heated on an electric stove evenly transfers heat to the oil. The water is mixed with a stirrer. Due to the significant heat capacity of water, there are no sharp fluctuations in oil temperature during testing.
Before testing transformer oil, the Engler viscometer must be thoroughly rinsed and dried. After inserting a plug - 4 into a calibrated tube - 3 and placing a volumetric flask under the drain hole with a mark on the narrow neck of a volume of 200 ml, pour the oil into a brass vessel. After closing the lid, heat the water, stirring it with a stirrer - 5. When the required oil temperature is established, which is noted by a thermometer - T 2, the oil is poured into the flask to the mark of -200 ml. In this case, foam is not taken into account. The outflow time of this volume of oil is measured with a stopwatch.
Oil viscosity in degrees Engler is the ratio of the expiration time of 200 milliliters of oil heated to a temperature of 50 0 C to the expiration time of the same volume of distilled water at a temperature of 20 0 C.
Expiration time 200 ml. water at a temperature of 20 0 C is called water number of the device.
Along with conditional viscosity, dynamic and kinematic are distinguished. Dynamic viscosity -η is calculated by the formula:
, Pa. with,
where f is the force in (N) acting on the solid ball.
This force is equal to the weight of the solid ball minus (based on the law of Archimedes) the weight of the liquid of the volume of the ball; r, - ball radius, mm; V is the speed of the ball, m/s;
,
where k is a correction factor that takes into account the influence of the walls of the vessel; r, - vessel radius, m; l. - vessel height, m; ν - kinematic viscosity, m / s is calculated by the formula:
,
where ρ is the density of the test liquid, kg/m 3 . Kinematic viscosity is often measured in stokes (St) = 10 -4 m 2 /s.
To measure viscosity, in addition to the Engler viscometer, ball viscometers, rotational, plastic viscometers, electrorotational and capillary viscometers are used.
Ball viscometers are based on measuring the rate of immersion of a steel ball in a test liquid.
Rotational viscometers are structurally composed of two cylinders: an outer fixed cylinder and an inner one rotating around a vertical axis under the action of a certain force. The space between them is filled with the test liquid. The viscosity of the liquid is determined by the power consumption for the rotation of the inner cylinder or by the degree of slowing down of its rotation. With a certain design of the rotational viscometer, it is possible to combine the determination of the viscosity and electrical resistivity of the test liquid by the leakage current between the cylinders.
Plastic viscometers are able, along with viscosity, to determine the tensile strength.
Electrorotational viscometers allow you to directly read the viscosity value on the scale of the measuring device.
Capillary viscometers are used to measure kinematic viscosity.
From kinematic viscosity (m 2 /s) to conventional viscosity (°Oe) can be changed using table 2.
table 2
| Kinematic viscosity | Grad E | Kinematic viscosity | Grad E | Kinematic viscosity | Grad E | |||
| m 2 /s | cSt | WU | m 2 /s | cSt | WU | m 2 /s | cSt | WU |
| 0.000001 | 1.00 | 1.00 | 0.000024 | 24.0 | 3.43 | 0.000054 | 54.0 | 7.33 |
| 0.000002 | 2.00 | 1.10 | 0.000025 | 25.0 | 3.56 | 0.000055 | 55.0 | 7.47 |
| 0.000003 | 3.00 | 1.20 | 0.000026 | 26.0 | 3.68 | 0.000056 | 56.0 | 7.60 |
| 0.000004 | 4.00 | 1.29 | 0.000027 | 27.0 | 3.81 | 0.000057 | 57.0 | 7.73 |
| 0.0000045 | 4.5 | 1.34 | 0.000028 | 28.0 | 3.95 | 0.000058 | 58.0 | 7.86 |
| 0.000005 | 5.0 | 1.39 | 0.000029 | 29.0 | 4.07 | 0.000059 | 59.0 | 8.00 |
| 0.0000055 | 5.5 | 1.43 | 0.000030 | 30.0 | 4.20 | 0.000060 | 60.0 | 8.13 |
| 0.000006 | 6.0 | 1.48 | 0.000031 | 31.0 | 4.33 | 0.000061 | 61.0 | 8.26 |
| 0.0000065 | 6.5 | 1.53 | 0.000032 | 32.0 | 4.46 | 0.000062 | 62.0 | 8.40 |
| 0.000007 | 7.0 | 1.57 | 0.000033 | 33.0 | 4.59 | 0.000063 | 63.0 | 8.53 |
| 0.0000075 | 7.5 | 1.62 | 0.000034 | 34.0 | 4.72 | 0.000064 | 64.0 | 8.66 |
| 0.000008 | 8.0 | 1.67 | 0.000035 | 35.0 | 4.85 | 0.000065 | 65.0 | 8.80 |
| 0.0000085 | 8.5 | 1.62 | 0.000036 | 36.0 | 4.98 | 0.000066 | 66.0 | 8.93 |
| 0.000009 | 9.0 | 1.76 | 0.000037 | 37.0 | 5.11 | 0.000067 | 67.0 | 9.06 |
| 0.0000095 | 9.5 | 1.81 | 0.000038 | 38.0 | 5.24 | 0.000068 | 68.0 | 9.20 |
| 0.000010 | 10.0 | 1.86 | 0.000039 | 39.0 | 5.37 | 0.000069 | 69.0 | 9.34 |
| 0.000015 | 15.0 | 2.37 | 0.000045 | 45.0 | 6.16 | 0.000075 | 75.0 | 10.15 |
| 0.000020 | 20.0 | 2.95 | 0.000050 | 50.0 | 6.81 . | 0.000080 | 80.0 | 10.8 |
At > 8 . 10 -5 m 2 / s (80 cSt), the transition from one system to another is carried out according to the formula.
Oil switches and reactor equipment. In reactor equipment, they serve as a medium for extinguishing the arc.
Requirements
The electrical insulating qualities that transformer oils possess depend on dielectric losses. The dielectric strength of transformer oils can be greatly reduced by water and a variety of fibers. Therefore, these substances should not be in its composition. An important parameter is the pour point. To maintain mobility in the cold, this indicator for the working fluid should be -45 ° C and below. In order to remove heat with maximum efficiency, the liquid must have a minimum viscosity at a flash point, which for various grades should not be less than 150-95 ° C.
The most important parameter that transformer oils have is oxidation stability, or the ability to maintain a constant performance over a long period of time. Most of the grades of transformer oils used are stabilized with anti-oxidation additives such as ionol or agidol-1. Their action is based on the ability to react with active peroxide radicals formed during the chain reaction of hydrocarbon oxidation. Ionol-stabilized transformer fluids most often oxidize with a pronounced induction period.
In the initial stage, oils that remain susceptible to additives oxidize very slowly, since all oxidation sites that appear in the oil are suppressed by the inhibitor. As the additive is depleted, the rate of oxidation approaches that of the original oil. The additive is the more effective, the longer the induction cycle of oxidation. The effect of the additive is determined by the hydrocarbon composition of transformer oil and impurities of other non-hydrocarbon compounds that enhance oil oxidation (these are nitrogenous bases, naphthenic acids, oxygen-containing oxidation products).
Transformer oils are designed to isolate parts and assemblies of power transformers that are under voltage, to remove heat from parts that are heated during their operation, and to protect the insulation from moisture.
Options
Transformer oil, the characteristics of which are completely determined by its content, in turn, largely depends on the chemical composition of the feedstock and the cleaning methods used. In the used grades of transformer oils, there are differences in chemical composition and performance characteristics, and they are intended for different purposes. New oil-immersed transformers only require completely fresh oils that have never been used before. Each batch of liquid used for filling must have a manufacturer's certificate. Before pouring transformer oil from the refinery into a power transformer, it must be cleaned from moisture, gases and mechanical impurities.
Moisture can be contained in transformer oil in various forms. It can be a precipitate, an emulsion and a solution. Transformer oil before filling is subjected to complete purification from the moisture contained in the oil in the state of emulsion and in the form of sludge. As a solution, moisture does not significantly affect the loss tangent and dielectric strength, although it contributes to an increase in the oxidizability of the liquid for transformers and a deterioration in the stability of its composition. In this regard, obtaining the values of the breakdown voltage and the loss tangent that meet the standards cannot serve as a criterion for complete cleaning.
An important parameter is the density of the transformer oil. It must be known in order to calculate the mass of the product received by the enterprise. The density of transformer oil allows you to find out its hydrocarbon composition.
At a pressure value equal to atmospheric, there can be up to 10% air in the dissolved state in the transformer oil. If the power transformers are equipped with film and nitrogen protection, the special oil must be degassed before filling in order to achieve a residual gas content not exceeding 0.1% by weight.
After cleaning is done, there should be no mechanical impurities in the oil.
Oil measurement
Checking the parameters of oils is carried out by analyzing their electrical insulating and physico-chemical characteristics:
- electrical strength;
- loss tangent;
- measurement of moisture content;
- measurement of the gas content in oil by means of an absorbciometer consists in determining the degree of change in the residual pressure in a certain container after samples of the test liquid are poured into it;
- measurement of the quantitative composition of mechanical impurities by passing a sample dissolved in gasoline through a paper filter without ash content.
The method for determining the moisture content of oil is based on the fact that hydrogen is released during the reaction of moisture in the oil with oxygen hydride.
Transformer oil tests
Before the transformers are put into operation, the transformer oil is tested.
For transformer equipment, all rated voltages, oil tests from the on-load tap-changer tank are carried out in full accordance with the manufacturer's manual. Oil for equipment with a power of up to 630 kVA, which is installed in electrical networks, is allowed not to be tested.
Transformer oil is tested by customers in a certified laboratory, which is certified for the right to test it.
centrifugation
This method of processing transformer oil is to remove moisture and suspended particles under the influence of centrifugal forces. In this way, only moisture, which is in the form of an emulsion, and particles in the solid state are removed. The specific gravity of the particles during centrifugation must be greater than that of the transformer oil being processed. This method is mainly used to purify liquid for power transformers with voltage up to 35 kV, or to pre-treat it.
Filtration
The method consists in passing the oil through porous partitions, which retain all impurities contained in it.
adsorption treatment
The method of purification of transformer oil by adsorption is based on the absorption of water and other impurities by various adsorbents. They are used as synthetic zeolites, which have a high absorption capacity, especially in relation to water particles. Purification of transformer oil with zeolites makes it possible to remove moisture from its composition, which is in a state of solution.
vacuum processing
The degasser became the basic element of the cleaning method. Crude oil is first heated to a temperature of 50-60 °C. After that, oil is sprayed into the degasser at its first stage. Further, it flows in the thinnest stream along the surface of the Raschig rings. In this case, the first stage is subjected to evacuation by means of a vacuum pump. The released water and gas vapors are pumped out through an air filter and a zeolite cartridge. From the tank of the degasser of the first stage, the oil passes by gravity into the second stage, where it is finally dried and degassed. At the final stage, the transformer oil passes through a fine filter and is fed into the transformer.
used oil
Waste transformer oil is regenerated at serial oil recovery plants using silica gel.
Transformer oil GK
The technical fluid received the indicated marking on the basis of the method of its production. Transformer oil GK is obtained by hydrocracking technology. The raw material for its manufacture are paraffinic sour oils. This type of oil has high insulating properties and is recommended for use in a variety of high voltage equipment. Transformer oil GK contains the additive ionol and has the best antioxidant properties.
It would seem, where is the oil, and where are the electrical appliances? Especially transformers, inside which huge currents roam, and high voltage is formed. Nevertheless, such electrical installations work with the use of technical fluids, and this is by no means antifreeze or distilled water.
Probably everyone has seen huge transformers at substations and power units of industrial enterprises. All of them are equipped with expansion tanks in the upper part.
It is in these barrels that transformer oil is poured. It looks quite familiar to the layman: the body of the electrical installation (similar to the crankcase of a car engine), inside there are working units. And all this wealth is filled with oil to the very top. As we understand, we are not talking about the lubrication of parts: there are no moving parts in the transformer. 
Scope of transformer oil
First, let's dispel some stereotypes. There is a persistent misconception that all liquids are conductors. In fact, not all, and not as obvious as metals.
An important property of transformer oil is its high resistance to electric current. So high that the liquid is actually a dielectric (within reasonable limits, of course).
Such a characteristic as lubricity is the last thing interesting in electrics. But thermal conductivity, on the contrary, is very important.
We will talk about properties separately, they follow from two areas of application:
The performance of such devices is amazing: the voltage is several hundred thousand volts, and the current strength is up to 50 thousand amperes.
The oil in these devices has two functions. Of course, insulating properties, as in transformers. But the main purpose is the effective extinguishing of the electric arc.
When opening (closing) contacts on electrical switching devices with such parameters, an electric arc occurs that can destroy the contact group in several cycles.
Electric arc when opening contacts (incident at a substation) - video
However, problems arise only in the air. If the internal cavity is filled with transformer oil, sparks and arcs will not occur.
Note
For the sake of objectivity, we note: there is another solution. In addition to oil circuit breakers, vacuum circuit breakers are actively used. True, they qualitatively perform only one function: extinguishing the arc. The dielectric properties of vacuum are comparable to ordinary air.
However, this is a topic for another article.
Specifications of transformer oil
Just like mineral motor oil, transformer oil is produced by distillation of prepared crude oil (refined), by boiling raw materials. After sublimation at a temperature of 300°C - 400°C, the so-called solar distillate remains.
Actually, this substance is the basis for obtaining transformer oil. During purification, the saturation of aromatic carbons and non-carbon compounds is reduced. As a result, the stability of the product is improved.
During sublimation and separation of the distillate, physical and chemical processes can be controlled. By manipulating the basic raw materials and technology, it is possible to change the properties of transformer oil. They are determined by the resulting ratio of components: 
Interestingly, this product is environmentally friendly. During its production, use and disposal, the environmental impact is no higher than that of the feedstock (crude oil). The composition does not include additives synthesized artificially.
Like oil, oil for transformers and switches is non-toxic (as far as petroleum products are concerned), does not destroy the ozone layer, and decomposes in the natural environment without a trace.
One of the important characteristics is the density of transformer oil. A typical value lies in the range 0.82 - 0.89 * 10³ kg/m³. The numbers depend on the temperature: the operating range is within 0°C - 120°C.
When heated, it decreases, this factor is taken into account when designing the radiator cooling system of transformers.
Since oils are relatively versatile, this characteristic may vary depending on the needs of the customer. Transformer substations are located in various climatic zones, often in the conditions of the Far North and Siberia.
Not only density changes with temperature
The viscosity of transformer oil can drastically change the overall performance of an electrical installation.
| Indicators | TKp | Selective oil | T-1500U | gk | vg | AGK | MW |
| Kinematic viscosity, im2/s* at temperature | |||||||
| 50°C | 9 | 9 | - | 9 | 9 | 5 | - |
| 40°C | - | - | 11 | - | - | - | 3,5 |
| 20°C | - | 28 | - | - | - | - | - |
| -30°С | 1500 | 1300 | 1300 | 1200 | 1200 | - | - |
| -40°С | - | - | - | - | - | 800 | 150 |
| Acid number, mg KOH/g, no more | 0,02 | 0,02 | 0,01 | 0,01 | 0,01 | 0,01 | 0,02 |
| Temperature, °С | |||||||
| Flashes in a closed crucible, not below | 135 | 150 | 135 | 135 | 135 | 125 | 95 |
| Freezing, no higher | -45 | -45 | -45 | -45 | -45 | -60 | -65 |
The principle of operation of an oil transformer - video
- Heat removal - possible with a sufficiently liquid coolant. That is, for normal cooling of the electrical installation, the viscosity should be as low as possible.
- Extinguishing the electric arc. How it works? In a normal air environment, when opening (closing) contacts under high load, an arc similar to welding occurs.
Thick oil, mechanically, will not be able to quickly fill the space when the contacts move. The resulting air cavities will become the reason for arcing. Conversely, a sufficiently liquid fill will constantly maintain a bubble-free environment.
Flash and ignition
An interesting parameter from the point of view of the physics of the process is the flash point of transformer oil. For any petroleum product, this is the ignition temperature of the liquid medium when in contact with an open source of flame.
However, the conditions for combustion are not created inside the transformer, due to the lack of sufficient oxygen. But an open flame is theoretically possible: if a short-term arc is formed when the contacts are opened.
Therefore, the properties of oils are based on an increase in flash point. This value gradually decreases due to defects in transformer equipment. During normal operation, the flash point, on the contrary, increases. Permissible value - more than 155°C.
Electric arc or how transformers burn - video
To understand the mechanism, the flash point is related to the volatility of the oil. That is, it must be sufficiently liquid, but at the same time not pass into a gaseous state under normal operating conditions.
In addition to the traditional parameter, there is such a thing as the auto-ignition temperature, which is typical for transformers. In our case, this value is 350°C - 400°C.
If the windings are heated to such a temperature, an uncontrolled combustion and explosion of the transformer occurs. Fortunately, such cases are extremely rare. Of course, subject to the terms of use.
Therefore, along with the selection of high-quality oil, it is necessary to constantly monitor the condition of electrical installations. When conducting test fluid samplings, one can understand what problems there are in the transformer itself or the high-voltage circuit breaker. 
After the studies, such indicators as refraction of viscosity, density, dielectric properties, etc. are evaluated. The results are compared with the tabular values \u200b\u200bset by the standard for the use of oils.
The table shows the main indicators of transformer oil:
| temperature t, °C | Density p, kg/m3 | Cp, kJ/(kgK) | λ, W / (m "K) | a-10**8, m2/s | μ-10**4, Pass | v-10**6, m2/s | ß-10**4, K"1 | Rg |
| 0 | 892,5 | 1,549 | 0,1123 | 8,14 | 629,8 | 70:5 | 6,80 | 866 |
| 10 | 886.4 | 1,620 | 0,1115 | 7,83 | 335,5 | 37,9 | 6.85 | 484 |
| 20 | 880,3 | 1,666 | 0,1106 | 7,56 | 198,2 | 22,5 | 6,90 | 298 |
| 30 | 874,2 | 1,729 | 0,1008 | 7,28 | 128,5 | 14.7 | 6.95 | 202 |
| 40 | 868,2 | 1,788 | 0,1090 | 7,03 | 89.4 | 10,3 | 7,00 | 146 |
| 50 | 862,1 | 1,846 | 0,1082 | 6,80 | 65.3 | 7,58 | 7,05 | 111 |
| 60 | 856,0 | 1,905 | 0,1072 | 6,58 | 49,5 | 5,78 | 7,10 | 87,8 |
| 70 | 850,0 | 1,964 | 0,1064 | 6,36 | 38.6 | 4,54 | 7,15 | 71.3 |
| 80 | 843,9 | 2,026 | 0,1056 | 6,17 | 30.8 | 3,66 | 7,20 | 59,3 |
| 90 | 837.8 | 2.085 | 0,1047 | 6,00 | 25,4 | 3,03 | 7,25 | 50,5 |
| 100 | 831,8 | 2,144 | 0,1038 | 5,83 | 21.3 | 2,56 | 7,30 | 43.9 |
| 110 | 825,7 | 2,202 | 0,1030 | 5,67 | 18.1 | 2,20 | 7,35 | 38,8 |
| 120 | 819,6 | 2,261 | 0,1022 | 5,50 | 15.7 | 1,92 | 7,40 | 34,9 |
- cp is the specific mass heat capacity, without changing the operating pressure;
- λ - thermal conductivity: general coefficient;
- a - thermal conductivity: general coefficient;
- μ is the dynamic coefficient of viscosity;
- ν is the kinematic coefficient of viscosity;
- β is the volumetric expansion: overall coefficient;
- Pr is the Prandtl criterion.
Technical fluids to ensure the operation of transformer substations are purchased in huge volumes, which is quite expensive. Each batch is tested before use, and in the course of work.
Breakdown testing of transformer oil - video
Every year, technical fluid requires large-scale cleaning. This is done by special services. And every 5-6 years, regeneration is required (almost complete replacement of oil in the electrical installation). The procedure is not cheap, but without it, the operation of the transformer will become unsafe.
As a compromise, property restoration is widely used. Mining is delivered to a petrochemical enterprise, where the oil acquires its original properties. The cost of added additives is many times lower in comparison with a complete replacement of the material.
Secondary Characteristics of Transformer Oil
The resistance of an oil to oxidation is nothing more than a resistance to aging. There are two downsides to this phenomenon:
- The binding of active additives by oxygen molecules, which provide the basic parameters of the liquid.
- Deposition of oxidation products on the surfaces of transformer parts: windings, conductors, contact groups. This leads to a decrease in heat dissipation, followed by boiling of the oil at the points of contact.
- Ash content - the presence of impurities and the reason for their appearance. After washing the new oil, chemical detergents remain in its composition (this also applies to the regeneration of the old fluid).
If they are not removed, ash fractions are formed, which settle on the working parts of transformers and switches. To combat this phenomenon, additives are added to the oil that neutralize salt and soap deposits.
The pour point (pour point) characterizes the transformation of a liquid into a grease. This indicator (from -35°C to -50°C) is applicable only during cold start of the electrical installation. A working transformer is itself a source of heat, and keeps the liquid in working condition.