6. The limitation of the validity period has been removed according to protocol N 2-92 of the Interstate Council for Standardization, Metrology and Certification (IUS 2-93)

7. EDITION (June 2011) with Amendments No. 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 switches and other high-voltage equipment as the main electrical insulating material.

1. BRANDS

1. BRANDS

The following brands of transformer oils are installed:

TK - without additive (manufactured according to special orders for general technical purposes), it is not allowed to use for filling transformers;

T-750 - with the addition of (0.4 ± 0.1)% antioxidant additive 2.6 di-tertiary butylparacresol;

T-1500 - with the addition of at least 0.4% of an antioxidant additive 2.6 di-tertiary butylparacresol;

PT is a promising oil.

(Modified edition, Amendments 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 that was 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.

Indicator name	Norm for the brand				Test Method
	TC OKP 02 5376 0101	T-750 OKP 02 5376 0104	T-1500 OKP 02 5376 0105
1. Kinematic viscosity, m / s (cSt), no more:
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, ° С, not lower than
		Absence
6. Pour point, ° C, not higher
7. Soda test, optical density, no more
10. Color on the colorimeter CNT, CNT units, no more
11. Stability against oxidation, no more:
______________ * Probably a mistake in the original. GOST 6581 should be read. - Note from the manufacturer of the database. Notes: 1. For transformer oil of the TK brand, produced from Embensky oils and their mixtures with Anastasyevskaya oil, when tested for stability against oxidation in accordance with GOST 981, a mass of volatile low-molecular acids of 0.012 mg KOH per 1 g of oil is allowed, the acid number of oxidized oil is no more than 0, 5 mg KOH per 1 g of oil. 2. When producing transformer oils from Baku paraffinic oils, it is allowed to use urea dewaxing. 3. (Deleted, Rev. N 2).

(Modified edition, Amendments N 2, 3, Amendment).

3. SAFETY REQUIREMENTS

3.1. Transformer oils are low-hazard products and, in terms of the degree of exposure to the human body, belong to the 4th hazard class in accordance with GOST 12.1.007.

3.2. Transformer oils are, in accordance with GOST 12.1.044, flammable liquids with a flash point of 135 ° C.

3.3. The room in which work is carried out with oil must be equipped with supply and exhaust ventilation.

3.4. The maximum permissible 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 extinguishing means are used: sprayed water, foam; with volumetric quenching - carbon dioxide, composition of SLB, composition 3.5, steam.

Section 3. (Modified edition, Amendment N 3).

4. RULES OF ACCEPTANCE

4.1. Transformer oil is accepted in batches. A batch is considered to be any amount of oil produced in the course of the technological process, homogeneous in terms of quality, accompanied by one quality document containing data in accordance with GOST 1510.

(Modified edition, Amendment N 3).

4.2. The volume of samples is in accordance with GOST 2517.

4.3. If unsatisfactory test results are obtained for at least one of the indicators, repeated tests of a newly taken sample from the same sample are carried out.

Retest results apply to the entire batch.

(Modified edition, Amendment N 3).

5. TEST METHODS

5.1. Samples of transformer oils are taken in accordance with GOST 2517.

For a combined sample, take 3 dm3 of each brand of oil.

(Modified edition, Amendment N 1).

5.2. Soda test for T-750 and T-1500 oils 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 a temperature of 5 ° C should be transparent in transmitted light.

5.4. The sludge 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 determining the sediment and acid number - 14 hours.

The indicator of low molecular weight volatile acids is allowed to be determined under the 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 in accordance with GOST 859;

air consumption - 50 cm / min;

the duration of oxidation is 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 oil - 130 ° С, for Т-1500 oil - 135 ° С,

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,

the catalyst is a copper plate;

oxygen consumption - 50 cm / min;

the duration of the oxidation is 30 hours.

(Changed edition, Rev. N 1, 2, 3).

5.5. The tangent of the dielectric loss angle of transformer oils is determined without preparation or after preparation in one of the following ways:

a) 100 cm3 of oil is kept for 30 minutes at 50 ° C at a residual pressure of 666.6 Pa (5 mm Hg) in a vessel with a free surface equal to 100 cm;

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 disagreements arising in the assessment of product quality, the preparation of the oil before determining the tangent of the dielectric loss angle is carried out according to subparagraph a.

To determine the tangent of the dielectric loss angle, electrodes made of stainless steel 12X18H9T or 12X18H10T in accordance with GOST 5632 are used. When manufacturing electrodes from copper in accordance with GOST 859 and brass in accordance with GOST 17711, the working surfaces of the electrodes must be coated with nickel, chrome or silver. The determination is carried out at an electric field strength of 1 kV / mm.

6. PACKAGING, LABELING, TRANSPORTATION AND STORAGE

6.1. Packaging, labeling, transportation and storage of transformer oils - in accordance with GOST 1510.

6.2. On the document certifying the quality of transformer oil of the T-750 and T-1500 grades of the highest category, and on the container, the State Quality Mark must be depicted.

7. MANUFACTURER'S WARRANTIES

7.1. The manufacturer guarantees the conformity of the quality of transformer oil to the requirements of this standard, subject to the conditions of transportation and storage.

7.2. The guaranteed shelf life of transformer oils is five years from the date of manufacture.

(Modified edition, Amendment N 2).



Electronic text of the document
prepared by JSC "Kodeks" and verified by:
official publication
Oil and oil products. Oils.

Technical conditions. Collection of GOSTs. -

M .: Standartinform, 2011

It would seem, where is the oil, and where are the electrical appliances? Moreover, transformers, inside which huge currents wander, and a high voltage is formed. Nevertheless, such electrical installations operate with the use of technical fluids, and this is by no means antifreeze and not distilled water.

Probably everyone has seen huge transformers at substations and power units of industrial enterprises. All of them are equipped with expansion tanks at the top.

It is into these barrels that transformer oil is poured. It looks quite familiar to the layman: the body of the electrical installation (by analogy with 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 it, we are not talking about the lubrication of parts: there are no moving parts in the transformer.

Application area of ​​transformer oil

First, let's dispel some stereotypes. There is a persistent misconception that all fluids are conductors. In fact, far from 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 reason, of course).

Such a characteristic as lubricity is the last interesting thing in electricians. On the other hand, thermal conductivity is very important.

Let's talk about the properties separately, they follow from two areas of application:

The performance indicators of such devices are 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 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 contacts open (accident at a substation) - video

However, problems arise only in the air environment. If the inner cavity is filled with transformer oil, arcing and arcing will not occur.

For your information

For the sake of objectivity, we note: there is another solution. In addition to oil circuit breakers, vacuum switches are actively used. True, they perform only one function qualitatively: arc extinguishing. The dielectric properties of vacuum are comparable to those of ordinary air.

However, this is a topic for another article.

Technical characteristics of transformer oil

As well as 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 diesel distillate remains.

Actually, this substance is the basis for obtaining transformer oil. During cleaning, the saturation of aromatic carbons and non-carbon compounds is reduced. As a result, the stability of the product is increased.

By sublimation and separation of distillate, physical and chemical processes can be controlled. By manipulating the basic raw materials and technology, it is possible to change the properties of the transformer oil. They are determined by the resulting ratio of components:

Interestingly, this product is environmentally friendly. During its production, use and disposal, the impact on nature is not higher than that of the feedstock (crude oil). The composition does not include artificially synthesized additives.

Like oil, oil for transformers and switches is not toxic (as far as it can be said about petroleum products), does not deplete the ozone layer, and decomposes without a trace in the natural environment.

One of the important characteristics is the density of the transformer oil. Typical values ​​are in the range 0.82 - 0.89 * 10³ kg / m³. The numbers depend on the temperature: the operating range is 0 ° C - 120 ° C.

When heated, it decreases, this factor is taken into account when designing a radiator cooling system for transformers.

Since oils are relatively versatile, this characteristic can vary depending on the needs of the customer. Transformer substations are located in different climatic zones, often in the Far North and Siberia.

Not only does density change with temperature

The viscosity of transformer oil can radically change the overall performance of an electrical installation.

Indicators	TKp	Selective refined oil	T-1500U	gk	vr	AGK	Mw
Kinematic viscosity, im2 / s * at temperature
50 ° C	9	9	-	9	9	5	-
40 ° C	-	-	11	-	-	-	3,5
20 ° C	-	28	-	-	-	-	-
-30 ° C	1500	1300	1300	1200	1200	-	-
-40 ° C	-	-	-	-	-	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 lower	135	150	135	135	135	125	95
Freezing, no higher	-45	-45	-45	-45	-45	-60	-65

This parameter is a product of compromise. To ensure the dielectric strength of the oil, the viscosity must be high. Almost like a solid dielectric. But the insulation of conductors is not the only purpose of the liquid in question.

The principle of operation of an oil transformer - video

• Heat removal - possible with a sufficiently liquid heat carrier. That is, for normal cooling of the electrical installation, the viscosity should be as low as possible.
• Electric arc extinguishing. How it works? In a normal air environment, when the contacts open (close) under a high load, an arc similar to a welding one arises.

Thick oil, mechanically will not be able to quickly fill the space when the contacts move. The resulting air pockets will cause arcing. Conversely, a sufficiently liquid filler will maintain a bubble-free environment at all times.

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 products, this is the ignition temperature of the liquid medium upon contact with an open flame source.

However, combustion conditions 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, an increase in the flash point is incorporated into the properties of oils. This value is gradually decreasing due to defects in the transformer equipment. On the other hand, the flash point increases during normal operation. Acceptable value is 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 go into a gaseous state under normal operating conditions.

In addition to the traditional parameter, there is such a concept as the self-ignition temperature, which is characteristic specifically for transformers. In our case, this value is 350 ° C - 400 ° C.

If the windings are heated to such a temperature, uncontrolled combustion and explosion of the transformer occurs. Fortunately, such cases are extremely rare. Of course, provided that the operating conditions are observed.

Therefore, along with the selection of high-quality oil, it is necessary to constantly monitor the condition of electrical installations. When carrying out test fluid withdrawals, you can understand what problems there are in the transformer itself or in the high-voltage switch.

After the research carried out, indicators such as refractive viscosity, density, dielectric properties, etc. are evaluated. The results are compared with the tabular values ​​established by the oil application standard.

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 - specific mass heat capacity, without changing the working pressure;
• λ - thermal conductivity: general coefficient;
• a - thermal conductivity: total coefficient;
• μ is the dynamic coefficient of viscosity;
• ν is the kinematic coefficient of viscosity;
• β - volumetric expansion: general coefficient;
• Pr is the Prandtl test.

Technical fluids to ensure the operation of transformer substations are purchased in huge volumes, it is quite costly. Each batch is tested before use and during operation.

Breakdown test of transformer oil - video

Every year, the technical fluid requires extensive cleaning. This is done by special services. And every 5-6 years, regeneration is required (almost complete oil change 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. The development is handed over to a petrochemical plant, where the oil acquires its original properties. The cost of the added additives is many times lower in comparison with the complete replacement of the material.

Secondary characteristics of transformer oil

The oxidation stability of an oil is nothing more than anti-aging. There are two negative sides to this phenomenon:

1. Binding of active additives by oxygen molecules, which provide the basic parameters of the liquid.
2. Deposition of oxidation products on the surfaces of transformer parts: windings, conductors, contact groups. This leads to a decrease in heat dissipation, with the subsequent boiling of the oil at the points of contact.
3. Ash content is the presence of impurities and the reason for their appearance. After flushing 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 are deposited on the working parts of transformers and switches. To combat this phenomenon, additives are added to the oil to 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 with a cold start of the electrical installation. A working transformer is itself a source of heat and keeps the fluid in working order.

The viscosity of transformer oil is an important physical parameter, it determines the process of heat transfer of windings and magnetic circuits in transformers and the arc-extinguishing capacity of switches.For good oil circulation in transformers, which improves the cooling of windings and magnetic circuits, low viscosity oils are required. In turn, oil, like other liquid dielectrics, viscosity increases strongly with decreasing temperature. At a temperature of 20 ° C, the viscosity of the transformer oil should be no more than 4.2 ° Oe and no higher than 2 ° Oe at a temperature of 50 ° C.

To measure the relative viscosity - VU of oil, an Engler viscometer is used, the diagram of which is shown in Fig. 3. Brass vessel - 2 is placed inside the 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

Schematic diagram of an 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 indicator pins - 5. Simultaneous contact with oil of all three points is a sign of correct installation on the table, inaccuracy of installation is straightened with 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 stirred with a stirrer. Due to the significant heat capacity of water, there are no sharp fluctuations in oil temperature during testing.

Before testing the transformer oil, the Engler viscometer must be thoroughly rinsed and dried. After inserting the plug - 4 into the 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 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 indicated by a thermometer - T 2, the oil is poured into the flask until the mark is 200 ml. In this case, the foam is not taken into account. The time that this volume of oil flows out is measured with a stopwatch.

Oil viscosity in Engler degrees is the ratio of the expiration time of 200 milliliters of oil heated to a temperature of 50 ° C to the expiration time of the same volume of distilled water at a temperature of 20 ° C.

Expiration time 200 ml. water at a temperature of 20 0 С is called water number of the device.

Along with the 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 a solid ball.

This force is equal to the weight of the solid ball minus (based on Archimedes' law) the weight of the liquid in the volume of the ball; r, is the radius of the ball, mm; V is the speed of the ball, m / s;

,

where k is a correction factor that takes into account the effect of the vessel walls; r, is the radius of the vessel, 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 ones are used.

Ball viscometers are based on the measurement of the immersion speed of a steel ball in a test liquid.

Rotational viscometers structurally consist of two cylinders: an external fixed one and an internal 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 deceleration of its rotation. With a certain design of the rotary viscometer, it is possible to combine the determination of the viscosity and specific electrical resistance of the test liquid by the leakage current between the cylinders.

Plast viscometers are capable of determining the ultimate strength, along with viscosity.

Electro-rotational viscometers allow you to directly read the value of the viscosity on the scale of the measuring device.

Capillary viscometers are used to measure kinematic viscosity.

From kinematic viscosity (m 2 / s) to conditional viscosity (° Oe) can be passed 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

For> 8. 10 -5 m 2 / s (80 cSt) the transition from one system to another is made according to the formula.

Introduction

Any power engineer knows firsthand what a transformer is and how it works. What is needed for the reliable operation of a transformer? One of the criteria is transformer oil. This work will help you learn more about transformer oil. She will tell not only about the oil itself, but also about the methods of drying it, as well as about the technical requirements for operation.

Transformer oil

Physical indicators

The density of transformer oils ranges from 800-890 kg / m 3 and depends on its chemical composition. The more polycyclic aromatic and naphthenic hydrocarbons in the oil, the higher its density. The molecular weight of transformer oils ranges from 230-330 and depends on their fractional and chemical composition. With a close fractional composition, the more aromatic hydrocarbons in the oil, the lower the molecular weight and density, that is, as the oil purification deepens, the density decreases and its molecular weight increases.

The molecular weight of oils is determined by ebullioscopic or cryoscopic methods. Both methods are based on the laws of dilute solutions: the first is to measure the rise in the boiling point of a pure solvent, and the second is to measure the decrease in the crystallization temperature of a pure solvent. Since polycyclic aromatic and naphthenoaromatic hydrocarbons tend to associate, the molecular weight is determined at different concentrations of oil in the solvent and the true molecular weight is calculated by extrapolation to zero concentration.

The refractive index characterizes the change in the speed of light when passing from one medium to another and is measured by the ratio of the sine of the angle of incidence of light to the sine of the angle of refraction. The refractive index depends on the wavelength of light and temperature and at the given values ​​of these parameters is a characteristic of the substance. Similar to density, the refractive index value decreases as cleaning is deepened. With close fractional composition and viscosity of oils, the refractive index satisfactorily characterizes the content of aromatic hydrocarbons.

Viscosity characterizes the property of a liquid to resist when one part of the liquid moves relative to another (Figure 1).

Usually they use the concept of kinematic viscosity, which is the ratio of dynamic viscosity to density; it is taken as a unit in the SI system 1 m 2 / s.

Viscosity is sometimes expressed in other units - Engler's degrees. Abroad, they use Saybolt and Redwood degrees.

In practice, it is often important to know the viscosity of the oil at low temperatures, the experimental determination of which is difficult. For this purpose, the viscosity is determined at two positive temperatures, the values ​​of their straight line on the nomogram are connected and extrapolated to the desired temperature (Figure 1).

Picture 1

It should be borne in mind that the nomogram is based on the assumption that in the accepted temperature range the oil manifests itself as a Newtonian liquid.

At temperatures close to the pour point, a viscosity anomaly appears. You can use the nomogram up to temperatures 10-15 ° C above the pour point.

In practice, the Dean and Davis viscosity index is widely used. These authors proposed to compare the viscosity of the test oil with the viscosity of oil distillates obtained from American oils from the Pennsylvania and Gulf of Mexico. The viscosity index of the first oil is taken as 100, and the second as 0.

All oils at 98.9 ° C must have the same viscosity.

The density, refractive index and viscosity of oils depend on the chemical and, first of all, the hydrocarbon composition of the oils with a similar fractional composition.

The flash point of transformer oils is determined in a closed crucible in a Martin-Pensky apparatus.

Flash point refers to the temperature at which balls of oil heated under standard conditions ignite when a flame is brought up to them.

The flash point for common commercial oils ranges from 130-170, and for arctic oil - from 90 to 115 ° C and depends on the fractional composition, the presence of relatively low-boiling fractions and, to a lesser extent, on the chemical composition.

The flash points of oils are dependent on their saturated vapor pressure. The lower the vapor pressure, the higher the flash point, the better the oil can be degassed and dried prior to pouring into high voltage equipment. The minimum flash point of oils is regulated not so much for fire safety reasons, but in terms of the possibility of deep degassing.

With regard to fire safety, the autoignition temperature plays an important role; this is the temperature at which oil, in the presence of air, ignites spontaneously without bringing up a flame. For transformer oils, this temperature is about 350-400 ° C.

In domestic transformer oils, the saturated vapor pressure at 60 ° C ranges from 8 to 0.4 Pa. Foreign oils, as a rule, have a lower vapor pressure and range from 1.3 to 0.07 Pa.

Transformer oil is a refined oil fraction, that is, it is a mineral oil. It is obtained by distillation of oil, where this fraction boils at 300 - 400 ° C. Depending on the grade of the feedstock, the properties of transformer oils are different. The oil has a complex hydrocarbon composition, where the average molecular weight varies from 220 to 340 amu. The table shows the main components and their percentage in the composition of transformer oil.

The properties of transformer oil as an electrical insulator are mainly determined by the value. Therefore, the presence of water and fibers in the oil is completely excluded, since any mechanical impurities worsen this indicator.

The pour point of transformer oil is from -45 ° C and below, this is important to ensure its mobility in low-temperature operating conditions. The lowest oil viscosity contributes to efficient heat dissipation, even at temperatures from 90 to 150 ° C in case of outbreaks. For different brands of oils, this temperature can be 150 ° С, 135 ° С, 125 ° С, 90 ° С, not lower.

An extremely important property of transformer oils is their stability under oxidation conditions; transformer oil must maintain the required parameters for a long period of operation.

As for the RF specifically, all grades of transformer oils used in industrial equipment are necessarily inhibited by an antioxidant additive - ionol (2,6-di-tertiary butylparacresol, also known as agidol-1). The additive interacts with active peroxide radicals arising in the chain of the oxidative reaction of hydrocarbons. Thus, inhibited transformer oils have a pronounced induction period during oxidation.

At first, oils susceptible to additives oxidize slowly as the resulting oxidation chains are interrupted by the inhibitor. When the additive is depleted, the oil oxidizes at the normal rate as without the additive. The longer the induction period of oil oxidation, the higher the effectiveness of the additive.

A lot of the effectiveness of the additive is associated with the hydrocarbon composition of the oil, and with the presence of non-hydrocarbon impurities that promote oxidation, which can be nitrogenous bases, petroleum acids and oxygen-containing products of oil oxidation.

When the petroleum distillate is refined, the aromatic content is reduced, non-hydrocarbon inclusions are removed, and ultimately the stability of the ionol-inhibited transformer oil is improved. Meanwhile, there is an international standard “Specification for Fresh Petroleum Insulating Oils for Transformers and Circuit Breakers”.

Transformer oil is flammable, biodegradable, almost non-toxic and does not harm the ozone layer. The density of transformer oil ranges from 840 to 890 kilograms per cubic meter. One of the most important properties is viscosity. The higher the viscosity, the higher the dielectric strength. At the same time, for normal operation in and in circuit breakers, the oil should not be very viscous, otherwise the cooling of the transformers will not be effective, and the circuit breaker will not be able to quickly break the arc.

A compromise is needed here regarding viscosity. Typically, the kinematic viscosity at 20 ° C, for most transformer oils, lies in the range from 28 to 30 mm2 / s.

Before filling the apparatus with oil, the oil is purified using deep thermal vacuum treatment. According to the current guidance document "Scope and Test Standards for Electrical Equipment" (RD 34.45-51.300-97), the air concentration in transformer oil, poured into transformers with nitrogen or film protection, into sealed instrument transformers and sealed bushings, should not be higher than 0, 5 (determined by gas chromatography), and the maximum water content is 0.001% by weight.

For power transformers without film protection and for leaky bushings, a water content of no more than 0.0025% of the mass is permissible. As for the content of mechanical impurities, which determines the oil purity class, it should not be worse than the 11th for equipment with a voltage of up to 220 kV, and no worse than the 9th for equipment with a voltage higher than 220 kV. The breakdown voltage, depending on the operating voltage, is given in the table.

When oil is filled, the breakdown voltage is 5 kV lower than that of oil before filling into the equipment. A decrease in the cleanliness class by 1 and an increase in the percentage of air by 0.5% is permissible.

Oxidation conditions (method for determining stability - according to GOST 981-75)

The pour point of the oil is determined in a test where a tube of thickened oil is tilted 45 ° and the oil remains at the same level for a minute. For fresh oils, this temperature should not be lower than -45 ° C.

This parameter is of key importance for. However, in different climatic zones, the pour point requirements are different. For example, in the southern regions it is allowed to use transformer oil with a pour point of -35 ° C.

Depending on the operating conditions of the equipment, the standards may vary, there may be some deviations. For example, arctic grades of transformer oil should not solidify at temperatures above -60 ° C, and the flash point drops to -100 ° C (flash point is the temperature at which heated oil produces vapors that become flammable when mixed with air).

In general, the flash point should not be lower than 135 ° C. Also important are characteristics such as the ignition temperature (the oil ignites and burns at it for 5 or more seconds) and the autoignition temperature (at a temperature of 350-400 ° C, the oil ignites even in a closed crucible in the presence of air).

Transformer oil has a thermal conductivity of 0.09 to 0.14 W / (m × K), and it decreases with increasing temperature. The heat capacity, on the other hand, increases with increasing temperature, and can be from 1.5 kJ / (kg × K) to 2.5 kJ / (kg × K).

The coefficient of thermal expansion is associated with the standards for the size of the expansion tank, and this coefficient is in the region of 0.00065 1 / K. The resistivity of transformer oil at 90 ° C and under conditions of an electric field strength of 0.5 MV / m in any case should not be higher than 50 Ghm * m.

As well as viscosity, oil resistivity decreases with increasing temperature. Dielectric constant - in the range from 2.1 to 2.4. The tangent of the dielectric loss angle, as mentioned above, is associated with the presence of impurities, so for pure oil it does not exceed 0.02 at 90 ° C under conditions of a field frequency of 50 Hz, and in oxidized oil it can exceed 0.2.

The dielectric strength of the oil is measured during a 2.5 mm breakdown test with an electrode diameter of 25.4 mm. The result should not be lower than 70 kV, and then the dielectric strength will be at least 280 kV / cm.

Despite the measures taken, transformer oil can absorb gases and dissolve a significant amount of them. Under normal conditions, 0.16 milliliters of oxygen, 0.086 milliliters of nitrogen and 1.2 milliliters of carbon dioxide will easily dissolve in one cubic centimeter of oil. Obviously, oxygen will begin to oxidize a little. If gases are released on the contrary, this is a sign of a winding defect. So, by the presence of gases dissolved in transformer oil, defects of transformers are revealed through chromatographic analysis.

The service lives of transformers and oil are not directly related. If the transformer is capable of operating reliably for 15 years, then it is advisable to clean the oil every year, and regenerate after 5 years. However, to prevent the rapid depletion of the oil resource, quite specific measures are provided, the adoption of which will significantly extend the service life of the transformer oil:

Installation of expanders with filters to absorb water and oxygen, as well as gases emitted from oil;

Avoiding working oil overheating;

Periodic cleaning;

Continuous oil filtration;

The introduction of antioxidants.

High temperatures, the reaction of oil with conductors and dielectrics - all this promotes oxidation, which is intended to prevent the antioxidant additive mentioned at the beginning. But regular cleaning is still required. High-quality cleaning of the oil returns it to a usable condition.

What can serve as a reason for the withdrawal of transformer oil from service? It can be contamination of the oil with permanent substances, the presence of which did not lead to deep changes in the oil, and then it is enough to carry out mechanical cleaning. In general, there are several cleaning methods: mechanical, thermophysical (distillation) and physicochemical (adsorption, coagulation).

If an accident occurs, the breakdown voltage has dropped sharply, carbon deposits have appeared, or chromatographic analysis has revealed a problem, the transformer oil is purified directly in the transformer or in the switch, simply by disconnecting the device from the network.

When regenerating used transformer oil, up to 3 fractions of base oils are obtained for the preparation of other commercial oils, such as motor, hydraulic, transmission oils, cutting fluids and greases. On average, after regeneration, 70-85% of oil is obtained, depending on the applied technological method. Chemical regeneration is more expensive. When regenerating transformer oil, it is possible to obtain up to 90% of the base oil of the same quality as the fresh one.