Monday, June 3, 2019
Transformer Oil Or Insulating Oil Engineering Essay
Transformer embrocate Or Insulating embrocate colour Engineering EssayCHAPTER 2LITERATURE go over2.1 IntroductionTransformer is ace of the most useful appliances ever invented. Transformer deal raise or lower the potential or legitimate in change current (AC) ne devilrk, the circuit can be isolated from one another, and to increase or decrease the apparent value of a capacitor, inductor, or resistor. Furthermore, the transformer allows us to transmit electrical energy long distances and to circulate safely in factories and homes. (Electrical Machines, Drives, and ability Systems, 6th Edition).The cost of a transformer is high. The failure of one transformer solvented in a loss in impairment of the price of one transformer or in terms of energy supply disruptions to consumers. thitherfore, to admonisher the transformer fossil vegetable crude anoint is one the right way and good for detecting the causes of damage to transformers.2.2 TransformerTransformer is one of the most important electrical devices. Transformer is wide use in power systems and electronic devices. Transformer can also raise and lower emf levels and the alternating current to suit finishing. Transformer can transfer power from one section to another on the same frequency but different potential levels and currents. Transformer fundamentally consists of two bankrolls of a conductor which acts as an inductor electrically separate but magnetically attached.Transformer consists of two loops wrapped around the core base, core and c anoint which are a part of the transformer structures. strain 2.1 shows the familiar structure of a transformer.When alternating current connected to the transformer primary voluminouss, current will flow through with(predicate) the primary convoluted. Alternating current flows will create an alternating magnetic flux in the transformer core. The magnetic flux can flow to the secondary winding of the transformer through the transformer core.http//w ww.electricityforum.com/images/electrical-transformer-design.jpgFigure 2.1 General Structure of TransformerAccording to the Faraday law, the electromotive force or potential is generate in the c anoint color-winding transformer when the flux is changes in value. Because of the magnetic flux in the transformer core is an alternating flux whose value is constantly changing over time, the electromotive force or voltage is always induced in the c vegetable anoint-winding transformer.Electromotive force in the primary winding is known as the self-induced electromotive force is due to the flux generated by the coil itself. While the electromotive force induced in the secondary winding is known as mutual induction electromotive force due to the induced electromotive force is ca utilize by magnetic flux generated from the primary winding.In an desirel transformer, the induced voltage in the secondary winding (Vs) is in proportion to the primary voltage (Vp), and is granted by the ratio of the enumerate of turns in the secondary (Ns) to the number of turns in the primary (Np) as follows(Equation 2.1)By appropriate selection of the ratio of turns, a transformer thus allows an AC voltage to be stepped up by do Ns greater than Np, or stepped crush by making Ns less than Np.There are many types of transformer are designed to meet the specific industrial applications. These embarrass autotransformer, control, current, distribution, general-purpose, instrument, isolation, potential (voltage), power, step-up, and step-down.To avoid rapid damage of the insulating materials inside a transformer, sufficient cooling of the windings and the core must be provided.Indoor transformers below 200 kVA can be directly cooled by the natural flow of the meet air. The metallic housing is equipped with ventilating louvres so that the convection currents that can flow over the windings and around the core. rangy transformers can be constructed in the same way, but the forced circul ation of fresh air must be provided. Such as a dry-type transformers are used inside the building, away from the hostile atmosphere.Distribution transformers below 200 kVA are usually immersed in mineral oil and sealed in a stain tank. Oil carries the heat away to the tank, which it is lost by radiation and convection to the outside air. Insulating oil is much better than air, consequently, it is often used in high voltage transformers.As the power rating increased, external radiators are added to increase cooling surface of the tank contains oil. Oil circulates around the transformer windings and moving through the radiator, where heat released into the surrounding air. For still higher(prenominal) levels, cooling fans blow air over the radiators.For transformers in the megawatt cast off, cooling can be effected by the oil-water system heat money changer. Hot oil drawn from the transformer tank is pumped into the heat exchanger where it flowing through the pipes that are in conta ct with cold water. Such as heat exchanger are very effective, but also very expensive, because water itself must continuously cool and recirculated.Some large transformers are designed to have triplex ratings, depending on the cooling method used. Thus, the transformer whitethorn have triple ratings depending on whether it is cooled bythe natural circulation of air (AO) for 18000 kVA, orforced-air cooling with fans (FA) for 24000 kVA, orthe forced circulation of oil accompanied by forced-air cooling (FOA) for 32000 kVA.These elaborate cooling systems are nevertheless economical because they enable a much greater output from the transformer of a given size and weight. The type of transformer cooling is designated by the following symbolsAA dry-type, self-cooledAFA dry-type, forced-air cooledOA oil-immersed, self-cooledOA/FA oil-immersed, self-cooled/forced-air cooledAO/FA/FOA oil-immersed, self-cooled/forced-air cooled/forced-air, forced-oil cooledThe temperature rise by the r esistance of oil-immersed transformers is either 55C or 65C. The temperature must be kept low to pre see the oil quality. By contrast, the temperature rise of dry-type transformer may be as high as 180C, depending on the type of separation used.TEMCo offers the largest selection of soaring Voltage Transformers.GE Ventilated Dry-type TransformerFigure 2.2 Dry-Type Transformer Figure 2.3 Oil-Immersed Transformer2.3 Transformer OilTransformer oil or insulating oil is usually a highly-refined mineral oil that is still at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers. Transformer oil is likened to be the blood within the transformer body. It must be periodically rilled to monitor condition of the transformer.Transformer oil serves three prefatory functions which are to insulate, to cool and maintain the transformer functions at all times. To keep these functions the industry has agreed on certain standards. The two leading transformer oil specifications in the world are IEC 60296 and ASTM D 3487. In these standards there are many specific requirement and limits based on physiological and chemical properties.Many of these properties and their limitations stem from the chemistry of refined mineral oils in combination with application specific requirements of electrical insulation. In an age when alternative to mineral oil being developed, it is important both to know what is desirable and what is likely to achieved in technical terms. Whereas some brands of transformer oil could solitary(prenominal) meet the specifications, the others excel.In the end, transformer oil consumers should decide which properties are most important to their intended use. Technical specifications also have an impact on issues such as asset management, maintenance training and investment budget. To aid decisions in these lands it is helpful to have a basic understanding of the science underlying specifications and limitat ions.In Malaysia, mostly used transformer oil is mineral crude oils (uninhibited mineral oils) which contains Paraffic, Naphteric or mixed. It is supplied by Hyrax Oil Sdn. Bhd.2.3.1 Transformer Oil PropertiesThe main function of transformer oil is insulating and cooling of the transformer. It should have the following propertiesHigh dielectric readiness and good dielectric properties resulting in minimum power loss.Low viscosity improves cooling.Freedom from inorganic red-hots, alkali, and corrosive sulphur.Resistant to emulsification.Rapid subsidence of arc products.Low pour loony toons.High flash crest resulting in low evaporation losses due to high thermal stability.High resistivity gives better insulation set mingled with windings.Excellent interfacial tension for quick water separation.Proven resistance to electrical stresses.High electrical dexterity. unusually low sludge and acidity formation in both ageing and oxidisation mental tests gives longer flavour to o il and equipment during storage and service.2.3.2 Theory of Transformer Oil Parameters pissing ContentThe standard for measuring water contain in oil is IEC 60814. (Marcel Dekker, 1990). The important function in transformer oil is to provide electrical insulation. When oil has higher moisture content, it can reduce the insulating properties of the oil, which may result in dielectric breakdown. This is the particular importance with fluctuating temperatures because, transformer will cools down if any dissolved water will become free and this oil become poor insulating power and fluid degradation. (Azliza binti Mohd Jelan,2009).Breakdown VoltageDielectric strength is one of the important properties in insulation field. Breakdown voltage in insulating material is the maximum electric field strength that it can be withstand intrinsically without breaking down and without experiencing failure of its insulating properties, dielectric strength also means that a certain configuration and e lectrode dielectric material that produces minimal damage to the electric field. (Rohaina bt Jaafar, 2003).Breakdown strength in swimming according to various factors influenced in the experiment which is electrode material and surface state, geometry electrode, the strawman of chemical pollutants, the presence of physical pollutants, oil molecular structure, temperature and pressure. There also various factors in the theory of voltage breakdown which is like electronic theory, suspended particle theory, cavitations theory and bubble theory were postulated. (Olive Oil from the channelise to the Table).Dielectric strength is also very dependent on the time and method of tension, purity materials, the type of tension as well as data-based and environmental parameters, until set of dielectric strength unique to the specific material is difficult, a range of values can be found and used for application purposes. (Noraniza binti Toriman, 2003).Figure 2.4 Heating / Cooling Curve of Oi l (Ahmad Norhakimi bin Ibrihim Ibrahim, 2010)2.3.3 Types of Transformer Oilmineral Transformer Oil (mineral Based Oil)A mineral oil or liquid petroleum is a liquid by-product of the distillation of petroleum to produce gasoline and other petroleum based products from crude oil. A mineral oil in this sense is a transparent, colourless oil composed mainly of alkenes (typically 15 to 40 carbons) and cyclic paraffin, related to petroleum jelly (also known as white petrolatum). It has a density of around 0.8 g/cm3. Mineral oil is a substance of relatively low value, and it is produced in very large quantities. Mineral oil is available in light and heavy grades, and can often be found in drug stores. There are three basic classes of refined mineral oilsParaffinic oils, based on n-alkenes.Naphthenic oils, based on cycloalkanes.Aromatic oils, based on aromatic hydrocarbons (not to be confused with essential oils).Table 2.1 Properties of Mineral Transformer Oil (http//www.substech.com)Prope rtyValue in metric unitValue in US unitDensity at 60F (15.6C)0.880 *10kg/m54.9lb/ftKinematic viscosity at 68F (20C)22cSt22cStKinematic viscosity at 212F (100C)2.6cSt2.6cStFire point170C338FPour Point-50C-58FFlash point160C320FAuto ignition point280C536FSpecific heat capacity1860J/(kg*K)0.444BTU/(lb*F) thermal conduction at 20C (68F)0.126W/(m*K)0.875BTU*in/(hr*ft*F)Thermal expansion at 20C (68F)7.5*10-4C4.2*10-4in/(in* F)Breakdown strengthmin.70kVmin.70kVDielectric dissolution factor at 90C (194F)max.0.002max.0.002Permittivity at 20C (68F)2.22.2Silicon Transformer Oil (Polydimethylsiloxane based fluid)Polydimethylsiloxane (PDMS) belongs to a group of polymeric organosilicon compounds that are commonly referred to as silicones. PDMS is the most widely used silicon-based organic polymer, and is particularly known for its unusual rheological (or flow) properties. PDMS is optically clear, and, in general, is considered to be inert, non-toxic and non-flammable. It is occasionally called dimethicone and is one of several types of silicone oil (polymerized siloxane). Its applications range from contact lenses and medical devices to elastomers it is present, also, in shampoos (as dimethicone makes hair shiny and slippery), caulking, lubricating oils, and heat-resistant tiles.Table 2.2 Properties of Silicon Transformer Oil (http//www.substech.com)PropertyValue in metric unitValue in US unitDensity at 60F (15.6C)0.960 *10kg/m59.9lb/ftKinematic viscosity at 68F (20C)55cSt55cStKinematic viscosity at 212F (100C)15cSt15cStFire pointmin.350Cmin.662FPour Pointmax.-50Cmax.-58FFlash pointmin.300Cmin.572FAuto ignition point435C815FSpecific heat capacity1510J/(kg*K)0.360BTU/(lb*F)Thermal conductivity at 20C (68F)0.15W/(m*K)1.019BTU*in/(hr*ft*F)Thermal expansion at 20C (68F)10.4*10-4C5.8*10-4in/(in* F)Breakdown strength50kV50kVDielectric dissipation factor at 90C (194F)max.0.001max.0.001Permittivity at 20C (68F)2.72.7Synthetic Transformer Oil (Organic Esters Based Fluid)Synthetic oil is a lubricant consisting of chemical compounds which are artificially made (synthesized) using chemically modified petroleum atoms rather than unanimous crude oil. Synthetic oil is used as a substitute for lubricant refined from petroleum when operating in extremes of temperature, because it generally provides superior robotlike and chemical properties than those found in traditional mineral oils.Table 2.3 Properties of Synthetic Transformer Oil (http//www.substech.com)PropertyValue in metric unitValue in US unitDensity at 60F (15.6C)0.970 *10kg/m60.6lb/ftKinematic viscosity at 68F (20C)70cSt70cStKinematic viscosity at 212F (100C)5.3cSt5.3cStFire point322C612FPour Point-60C-76FFlash point275C527FAutoignition point438C820FSpecific heat capacity1880J/(kg*K)0.448BTU/(lb*F)Thermal conductivity at 20C (68F)0.144W/(m*K)0.98BTU*in/(hr*ft*F)Thermal expansion at 20C (68F)7.5*10-4C4.2*10-4in/(in* F)Breakdown strengthmin.75kVmin.75kVDielectric dissipation factor at 90C (194F)max.0.006 max.0.006Permitivity at 20C (68F)3.23.22.3.4 Transformer Oil TestingRegular sampling and testing of insulation oil interpreted from transformers is a valuable technique in a preventative maintenance program. If a pro vigorous approach is adopted based on the condition of the transformer oil, the life of the transformer can be extended. Hence, transformer oil must be periodically tested to ensure its basic electrical properties. These tests can be divided intoLiquid Power FactorThe IEC standard method for this test is IEC 247. This involves measuring the power loss through a thin film of liquid test. Water, contamination, and the decay products of oil oxidation tend to increase the power factor of oil. The new oil has very low power factor less than 0.1% at 25 C and 1.0% at 90 C. As the oil ages and moisture accumulates, or if the unit is contaminated, the liquid power factor tends to increase. Many owners make the mistake of having this transformer testing at only one temperature. While the test is more sensitive to 90 C, both the temperature should be used. The relationship between 25 and 90 values can assist in making the diagnosis as to whether the problem of moisture, oxidation, or contamination. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY)Dielectric Breakdown StrengthThe dielectric breakdown voltage is a measure of the ability of the oil to withstand electric stress. Dry and clean oil showed the inherent high breakdown voltage. Free water and satisfying particles, especially the latter in combination with high levels of dissolved water, tend to migrate to areas of high electric stress and dramatically reduce the breakdown voltage. The meter of breakdown voltage, therefore, serves primarily to indicate the presence of contaminants such as water or conducting particles. A low breakdown voltage can be indicating that one or more of these are present. However, a high breakdown voltage does not necessarily indicate the absence of all contaminan ts. This test was conducted in symmetry with IEC 156. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY)MoistureThe purpose of dielectric tests are conducted is to ensure the monitoring moisture can be done directly. IEC 733 is a well established and can measure the moisture down to the low part of the million levels. While the acceptable values have been set by the voltage class for moisture, these are somewhat misleading. A truer picture of moisture in the transformer must be taken into account so that percentage saturation of the oil by moisture and percentage moisture by dry weight of the solid insulation can be calculated. A transformer at 20 C that containing 20 ppm moisture in oil is considerably wetter than a same unit, with a similar 20 ppm moisture, but it is operating at 40 C. The new transformer must be less than 0.5% moisture by dry weight. Anything more than 3.0% (or 30% saturation) is considered very wet. Many owners dehydrate transformer when the moisture level expire 1.5 to 2.0% moisture by dry weight. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY)Neutralization Number ( acetousity)This value, measured by IEC standard method IEC 1125A reported as mg KOH / g experiment, reports the relative amount of oil oxidation products, especially acids, alcohol and soap. As oil continues to oxidize, the acid increased gradually, generally over the years. Running the acid number regularly provides guidance as to how far oxidation of the oil has proceeded. The acceptable limit by the test is usually used as general guidelines to determine when the oil should be replaced or reclaimed. Acceptable values for acid number are 0.20 and lower. Unacceptable values are over 0.20.These are the values that are used by TNB. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY)Interfacial TensionThe test methods for interfacial tension (IFT), IEC 6295, measuring the strength in mN/m from the interface that will form between service aged oil and distilled w ater. Because the decay products of oil oxidation are oil and water soluble, their presence would tend to weaken the interface and reduce the interfacial tension value. Brand new oil is often 40-50 mN/m. A value that is acceptable for the in-service oil is greater than 25 mN/m or greater unacceptable results are below 28 mN/m. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY) illusion/VisualField inspection of liquid insulation (IEC 296) includes examination for the presence of cloudy or sediment and the general appearance as well as a colour inspection. As oil ages, it will be darken gradually. Very dark oil or oil that changes drastically over a short period of time may indicate a problem. Any cloudiness or sediment indicates the presence of free water or particles that may be harmful to continued the equipment operation. Taken alone, without considering the past history or other test parameters, the colour is not very important to diagnose transformer problems. If the oil has an acrid or unusual odor, consideration should be given to carrying out further tests. (A Guide To Transformer Oil Analysis, by I.A.R. GRAY) muck/SedimentThe IEC 296 test distinguishes between the sediment and sludge. Sediment is an insoluble substance present in the oil. Sediment may consist of insoluble oxidation or degradation products of solid or liquid materials, solid products such as carbon or metallic oxide and fibres or other foreign matter. Sludge is polymerized oxidation products of solid and liquid insulating material. Sludge is soluble in oil up to a certain limit. At sludge levels above this, the sludge comes out of the solution contributing an additional component to the sediment. The presence of sludge and sediment can change the electrical properties of the oil and prevent the exchange of heat, so encouraging damage to the insulating material. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY)Inhibitor ContentInhibited oil deteriorates more slowly than uninhibit ed oil so long as active oxidation inhibitor is present. However, later the oxidation inhibitor is consumed, the oil can be oxidized at a higher level. Determination of oxidation inhibitor remaining in the in-service transformer oil is based on IEC 666. (A Guide to Transformer Oil Analysis, by I.A.R. GRAY)Dissolved Gas AnalysisIn contrast to the tests and the methods discussed to this point, the dissolved gas analysis (DGA) did not measure the gradual changes in the quality of oil. DGA has a very limited utility in determining the continued suitability of the transformer oil. The purpose and functions of the DGA is to provide an indication as to whether there may be an active or incipient transformer fault affecting the operation and continued health of the equipment. DGA is used to detect and measure nine of dissolved gases which are Hydrogen, Oxygen, Nitrogen, Methane, light speed Monoxide, Carbon Dioxide, Ethan, Ethylene, and Acetylene. (A Guide To Transformer Oil Analysis, by I.A.R. GRAY)Dissolved Metals AnalysisAnalysis of dissolved metals (in particular, for the three metals iron, copper, and aluminium) can be used in further identifying the location of transformer faults discover by dissolved gas analysis. For example, the dissolved metal analysis indicating the presences of conductor metals may indicate a fault is occurring in the winding or at a connection while the presence of iron indicates involvement of the core steel. (A Guide To Transformer Oil Analysis, by I.A.R. GRAY)Furanic CompoundsWhen paper breaks down, the cellulose chains are broken and glucose molecules (which serve as the building blocks of the cellulose) are chemically changed. Each of the glucose monomer molecules that are removed from the polymer chain becomes one of a series of related compounds called furans or furanic compounds. Because these furanic compounds are partially soluble in oil, they are present in both the oil and the paper. Measuring the concentration of the oil c an tell us a petite more about the paper. The standard method typically tests for five compounds that are normally only present in the oil as a result of the paper breaking down. Those five compounds, and their probable causes, are 5-hydroxymethyl-2-furaldehyde, 5H2F (typically organise by oxidation of paper), 2-furyl alcohol, 2FOL (typically formed in connection with a high moisture content), 2-furaldehyde, 2FAL (very common, formed by all overheating and aging conditions), 2-acetyl furan, 2ACF (very rare, may be related to electrical stress), and 5-methyl-2furaldehyde, 5M2F (typically formed as a result of overheating). (A Guide To Transformer Oil Analysis, by I.A.R. GRAY)2.3.4 Instrument / Device for Transformer Oil TestingOil Test Set (Megger OTS 60 PB)The OTS 60PB is a 0 60 kV, battery powered portable dielectric strength oil test set. Its size and weight make it suitable for on-site assessment of insulating oil quality. The dielectric strength test it performs is an importa nt deciding factor in knowing whether to retain or replace the oil. Breakdown voltage is measured, averaged and displayed under the control of built-in programmed sequences. Go/no-go testing is available.Figure 2.4 Oil Test Set (Megger OTS 60 PB)OTS 60PB follows the oil testing sequences described in many national and other specifications among which are British BS 148, BS 5730a (automatic proof testing), BS 5874 International IEC 156, American ASTM D877 ASTM D1816, German VDE 0370, French NFC 27, Spanish UNE 21, Italian CEI 10-1, Russian GOCT 6581, South African SABS 555, Australian AS 1767 and Institute of vegetable oil IP 295. Two types of withstand (proof) testing of an oil sample are available. The principle with these tests is to subject the oil sample to a specified voltage for a defined length of time (1 minute) to see if it will withstand that voltage. In one of the tests the voltage is removed after a minute, in the other test, the voltage continues to rise after the minu te until breakdown or the maximum value is reached. confine (proof) tests can be set up to the users own requirements, and then repeatedly called up to quickly test oil under known fixed conditions.The OTS 60PB is used for determining the dielectric strength of liquid insulants such as insulating oils used in transformers, switchgear, cables and other electrical apparatus. It is portable and suitable for testing on site as well as in the laboratory. The test set is richly automatic. The operator has only to prepare the test vessel, load it with sample oil, place it in the test chamber, select the appropriate specification for the tests and then start the test sequence. The test set carries out automatically (and if necessary unattended) the sequence of tests as defined by the pre-selected national specification. Oil testing specifications, for which the set is pre-programmed, are as follows-Figure 2.5 Oil testing specificationsA 5 minute test sequence is also provided so that the operator may quickly obtain an idea of the breakdown value of an oil sample. Two types of semi automatic withstand (proof) testing of an oil sample are available. The principle with these tests is to subject the oil sample to a specified voltage for a defined length of time (1 minute) to see if it will withstand that voltage. In one of the tests the voltage is removed after a minute, in the other test the voltage continues to rise after passing for one minute until breakdown or the maximum value is reached. Withstand (proof) tests can be set up to the users own requirements, and then repeatedly called up to quickly test oil under known fixed conditions. The test results can be reviewed on the LCD or printed via the RS232 interface. An optional, battery operated printer is available to obtain a hard copy of the results. The safety features incorporated in the test sets design include two forced break switches used as described in BS 5304. These are interlocked with the oil vessel fr eightage door.volumetrical titration system Metrohm Titrino SM 702An automatic potentiometric titration system Titrino SM 702 with Exchange Unit 806 made by Metrohm measured the acidity of the oils. Here the Total Acid Number (TAN) was determined by a volumetric titration with potash to neutralize the carboxylic acids. The titration took place as follows At first 10 g of the oil were dissolved in 40 ml of solvent toluene / ethanol in a ratio of 5 to 4. Potash (KOH, 0,1 mol/l) was added as titre with volume increments of 0.001 ml or 0.005 ml depending on the expected acidity. The system detects, when the acid-base-equivalence-point EP is reached by a voltage measurement in the solution. From the volume of potash at the EP equation below calculates the acidity as TANTAN total acid numberEP1 equivalent pointC31 blind value of the solvent toluene/ethanolCO1 0.1 mol/L, concentration of titreCO2 1CO3 56106 g/mol, molar mass of titreCO0 weight of the oil sampleFigure 2.6 Volumetric itration systems Metrohm Titrino SM 702Kelman violate X Portable DGA Unit And Moisture In OilDissolved Gas Analysis (DGA) is an established technique and is recognised as the most important test in monitoring power transformers. It is now being successfully extended to other oil filled equipment such as tap changers and circuit breakers. The TRANSPORT X unit has been designed to be very rugged and user friendly with an emphasis placed on field operation. The unit is used by over 200 companies and utilities and has sold in excess of 600 units oecumenical.Figure 2.7 Kelman TRANSPORT X Portable DGA Unit And Moisture In OilThe TRANSPORT X test uses state of the art infrared measurement technology to give accurate, reliable results in a matter of minutes. The TRANSPORT X product represents an invaluable tool for Asset Management and will increase the power of any DGA program. Extensive field and laboratory use worldwide has proven that the TRANSPORT X test gives highly reliable result s and that it is genuinely suitable for field conditions. The TRANSPORT X equip
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