Prepared By:KAMAL DEEP

Roll No.115060

Sem:7th

INUSTRIAL TRANING AT NIT HAMIRPUR

TIFAC CORE means TECHNOLOGY INFORMATION FORCASTING AND ASSCEMENT COUNCIL CENTRE OF RELEVANC AND EXCELLENCE.

Abstract-Centre of Relevance & Excellence (CORE) in “Power Transformer Diagnostics” came into existence since 1 st September, 2004.

National Institute of Technology Hamirpur, Himachal Pradesh, India is one such centre in the area of Power Transformer Diagnostics established in September 2005. The activities of this centre are supported by TIFAC, an autonomous entity under Department of science and technology, Government of INDIA and from the Industry side by Himachal Pradesh State Electricity Board (HPSEB) Ltd.

SURVAY LITERATURE: Transformer failure statistics reported in literature indicate that most failures have occurred before reaching their expected designed life. Transformer failures related to transformer health conditions, such as dielectric problems.

Health Index: A Health Index is a means of combining information related to the physical condition of a transformer such as inspection results, test results or condition related risk factors, to provide a comparable measure of condition for individual transformers in terms of proximity to end of life or probability of failure.

41 % of failures were due to on-load tap changers (O.L.T.C) 19 % were due to the windings. 53 % mechanical and 31% dielectric On transformers without on-load tap changers

26.6 % of failures were due to the windings 6.4 % were due to the magnetic circuit 33.3 % were due to terminals 17.4 % were due to the tank and dielectric fluid 11 % were due to other accessories,

4.6 % were due to the tap changer

TIFAC CORE

TIFAC-CORE IN POWER TRANSFORMER DIAGNOSTICS

Research Areas Transformer Monitoring at site. Aging of solid insulation and improvements. Detection, location& deformation and intensity of winding deformation due to short-circuit. Performance evaluation of transformer feeding steel industry. Partial discharge measurement at site.

Objectives To develop expert manpower to cater to the needs of Industry and Academia in the targeted area, though suitable academic

activities (Elective courses and PG programe on Condition Monitoring of Power apparatus). To meet the training/retraining needs of manpower engaged in Power utilities all over the country in the area of power

transformer diagnostics. To create experimental facilities and infrastructure to carry out quality research through sponsored R & D projects. To establish linkage with pioneer organizations working in the focused area.

Major Facilities Insulation Analyzer (DOBLE) Domino Moisture in Oil Analyzer Portable Dissolved Gas Analyzer ADTR-2K, Automatic Capacitance and Tan Delta Test Set Breakdown Voltage Oil Test Set

High voltage are used for wide variety of applications covering the power systems, industry and research laboratories. High voltage are applied in laboratories in nuclear research, in partical accelerator and van de graaff generator.

Generation and transmission of electric energy The first public power station was put into service in 1882 in London. To produce direct current at low voltage. Its service was limited to highly localized areas. Used mainly for electric lighting. The first major AC power station was commissioned in 1890 at Deptford. To supply power over a distance of 28 miles. To produce alternative current at high voltage of 10 kV. Two principle factors influences the development of power transmission networks. To make full use of economic generation, transmission networks must be interconnected for pooling of generation

in an integrated system. Bulk transfer over long distances.

Generation and transmission of electric energy HVDC permits a higher power density as compared to AC transmission. HVDC provides an economic solution for interconnecting asynchronous AC systems (back-to-back installation). Major DC systems in chronological order of their installations

Introduction to High Voltage Technology

Voltage Stresses The IEC and its national counterparts (IET, IEEE, VDE, etc.) define high voltage circuits as those with more than

1000 V for AC and at least 1500 V for DC. In electric power transmission engineering, high voltages usually considered any voltage over approximately 35

kV. AC systems:

High voltage levels: 35-220 kV Extra high voltage (EHV) levels: ≥330 kV and <1000 kV Ultra high voltage (UHV) levels: 1000 kV and above

DC systems: HVDC levels: 600 kV and below UHVDC levels: above 600 kV

Operating voltage: Normal operating voltage does not severely stress the power system’s insulation. only in special circumstances, for example under pollution conditions, may operating voltages cause

problems to external insulation. operating voltage determines the dimensions of the insulation which forms part of electrical equipment.

Overvoltage's Voltage stresses on power systems arise from various overvoltage's. External overvoltage's: associating with lightning strokes on lines Internal overvoltage's: generated by changes in the operating conditions of systems, such as switching

operation (switching overvoltage), faults on systems or fluctuations in loads (voltage rise and fluctuation overvoltage).

Testing voltages It is necessary to test HV equipment during its development stage and prior to commissioning. The magnitude and type of test voltage varies with the rated voltage of a particular apparatus. Basic classification of testing voltages

◦ Testing with power frequency voltages

◦ Testing with lightning impulse voltages

◦ Testing with switching impulse voltages

◦ Testing with DC voltages

◦ Testing with very low-frequency voltages

High voltage engineering consists of generation, measurement, and control of high voltages, dielectric discharges and electrical insulation breakdown, over voltages and their protection, and

electrical insulation condition monitoring and diagnosis, et al.

Dielectrics and electrical insulation

Over voltages and Insulation coordination in electric power systems

High voltage testing techniques

I

Insulation

HV testing techniques Overvoltage

Relationships？

Main contents of the course

Electrical insulation Dielectrics or insulating material Properties and phenomenon of dielectrics in high fields. Insulation structures and electric field distribution How to design proper insulation structures to satisfy requirements of field distribution in or around HV equipment. Voltage stresses on electric insulation AC, DC, impulse, and combined voltages should be considered for insulation structure designing.

Over voltages Occurrence, development, propagation of over voltages and their influence factors. Approaches to limit overvoltage on HV systems. Coordination of voltage stresses, insulation, and overvoltage protection devices.

High voltage testing techniques How to generate high voltage Economic and flexible HV testing equipment How to execute high voltage experiment HV testing programs and standards How to measure high voltage Measurement of High field, tiny quantity of parameters of HV equipment of systems, transient parameter measurement.

MECHANISM OF BREAKDOWN OF GASES Gases have dielectric properties comparable or superior to each other. There are two basic reasons for

carrying out such investigations.◦ Firstly, the aims are to develop an insulating medium, which is technically as well as economically

attractive. ◦ The other reason is to obtain a better understanding of the breakdown mechanisms operating in

compressed gases, and their gas mixtures. Where a voltage difference exists between two conductors, it is necessary to keep them apart to prevent the

undesirable flow of electrical current from the one conductor to the other. When the conductors are separated (isolated from each other) a layer of gas (air) fills the space between them, forming the electrical insulation. the field strength in this gap will depend on the voltage difference and the gap size. if the field strength in the gap exceeds a certain threshold, the gas in the gap will seize to act as an insulating material, but will become ionized and break down. Prior to flashover, corona discharges occur in regions of high field strength.

The most commonly used insulating gas is air at atmospheric pressure, as employed on overhead power lines and open air substations.

Breakdown Voltage of Air

The breakdown in air (spark breakdown) is the transition of a non-sustaining discharge into a self-sustaining discharge. The buildup of high currents in a breakdown is due to the ionization in which electrons and ions are created from neutral atoms or molecules, and their migration to the anode and cathode respectively leads to high currents.

Flashover of uniform gaps: The effect of pressure and gap length: In small uniform gaps it has been found empirically that, at standard pressure (1 bar = 101,3

kPa = 760 mm Hg) and temperature (20 °C), that breakdown occurs at a field strength of approximately 30 kV/ cm.

At lower pressures the gas molecules are less densely packed and the mean free path between collisions is longer. The electrons therefore attain higher speeds before colliding with the gas molecules, resulting in a lower flashover stress for the same gap. At very low pressures, such as used in vacuum contactors, the gas atoms are so far apart that the collision probability is low, with the result that ionization and flashover takes place at a much higher value.

Two identical metallic spheres are separated by certain distance form a sphere gap. Also, the gap length between the spheres should not exceed a sphere radius. If these conditions are satisfied and the specifications regarding the shape, mounting, clearances of the spheres

Flashover of non-uniform gaps: the polarity effect If the voltage across a non-uniform field gap is increased, avalanche

activity occurs in the regions where the field is high . If the voltage is increased beyond the corona inception level, some

avalanches develop into streamer discharges, bridging the gap to cause a complete flashover. The flashover voltage of a non-uniform gap is therefore much lower than that of a uniform gap of the same size. The "rule of thumb" of 30 kV/ cm therefore does not apply to non-uniform gaps.

In this arrangement the ground effect also affects the breakdown voltage of

the rod-plate air gaps but in a quite different way than the Polarity Effect.

Corona discharges In the case of a non uniform gap the maximum field strength will occur near electrodes of small radius of curvature.

The ionization threshold is therefore exceeded only in these areas. Partial discharges or corona therefore occurs in these areas. Corona is a self-sustaining discharge, occurring in the parts of the gap where the critical field strength is exceeded. If the voltage is further increased, final flashover develops from the corona.

Apart from being a pre-cursor of flashover, corona is also undesirable on the power system due to the electromagnetic interference caused, the additional corona losses and the material (insulation) degradation due to the ultra violet radiation, emanating from the corona.

Problems caused by corona: Corona can be noticed as a bluish luminous discharge on conductors and ozone is formed. Interference (Radio Interference Voltage, RIV): The rapidly varying corona current pulses, especially the positive

streamer discharges, radiate electromagnetic interference in the range 0.2 to 10 MHz

Losses: The continuous corona current, shown in Figure 3.16, has a 50 Hz component that causes a power loss on the line.

Normally, a well designed transmission line will have a low amount of radio-interference (RI) and therefore also small losses. During rain, however, corona forms on droplets on the conductor and both RI and power losses occur. Under such conditions, losses of tens of MW can occur on a 500 kV line.

Measures to curb Corona: As corona is caused by the field intensification at sharp points, having a small radius of curvature. Sharp edges and points due

to poor workmanship on high voltage hardware must therefore be avoided. Lines are normally designed to limit the surface gradient to low values. For EHV lines it is necessary to use bundled conductors, i.e. each phase consists of a number of parallel conductors as explained in section 2.2.3. On the 800 kV lines 6 conductors are used. The six conductors are equivalent to one conductor with a large radius and the surface gradient and losses are therefore low. Likewise, a corona ring can be fitted to shield stress concentrations

Useful applications of Corona: Besides the nuisance value on the power system, corona has many useful applications, including: photocopying machines,

electrostatic dust precipitators and ozone generators.

INSULATORS An insulator, also called a “dielectric”, is a material that resists the flow of

electric current in it. An insulating material has atoms that has tightly bonded valence electrons. These materials are used in parts of electrical equipment, also called insulators, with the aim to support or separate electrical conductors without passing current through themselves. Some materials such as glass, paper or Teflon, mica are very good electrical insulators.

Solid and Liquid Insulating Materials The electrical performance of liquids and solids will be better than that

of gases. In practice, the electric strength of liquid and solid materials are however less than predicted due to impurities and imperfections.

Liquid and solid materials also classed as dielectrics, i.e. they have the property of polarization, resulting in a dielectric constant that is higher than unity.

Dielectric The dielectric consists of dipoles. The dipoles could be due to the positive and negative

charge carriers of the molecules not coinciding or could be due to the charge distribution in the crystal structure of the material. When not energized, the dipoles are randomly arranged. At the application of a voltage between the electrodes an electric field is established that acts on the dipoles to align them.

Breakdown Insulators suffer from the phenomenon of electrical breakdown. When the electric field applied across an

insulating substance exceeds the threshold breakdown field for that substance, which is proportional to the band gap energy of the insulating material, the insulator suddenly turns into a resistor, sometimes with disastrous results.

During electrical breakdown, any free charge carrier being accelerated by the strong e-field will have enough velocity to knock electrons from any atom it strikes. These free electrons and ions are in turn accelerated and strike other atoms, creating more charge carriers, in a chain reaction. Rapidly the insulator becomes filled with mobile carriers, and its resistance drops to a low level. In air, the outbreak of conductivity is called "corona discharge" or a "spark." Similar breakdown can occur within any insulator, even within the bulk solid of a material.

The electrical breakdown of an insulator due to excessive voltage can occur in one of two ways:

• Puncture voltage:- is the voltage across the insulator which causes a breakdown and conduction through the interior of the insulator. The heat resulting from the puncture arc usually damages the insulator irreparably.

• Flashover voltage:- is the voltage which causes the air around or along the surface of the insulator to break down and conduct, causing a 'flashover' arc along the outside of the insulator. They are usually designed to withstand this without damage.

Most high voltage insulators are designed with a lower flashover voltage than puncture voltage, so they will flashover before they puncture, to avoid damage.

BREAKDOWN IN SOLID

Solid insulating materials are used almost in all electrical equipments, be it an electric heater or a 500 MW generator or a circuit breaker, solid insulation forms an integral part of all electrical equipments especially when the operating voltages are high. The solid insulation not only provides insulation to the live parts of the equipment from the grounded structures, it sometimes provides mechanical support to the equipment. In general, of course, a suitable combination of solid, liquid and gaseous insulations areused.The processes responsible for the breakdown of gaseous dielectrics are governed by the rapid growth of current due to emission of electrons from the cathode, ionization of the gas particles and fast development of avalanche process. When breakdown occurs the gases regain their dielectric strength very fast, the liquids regain partially and solid dielectrics lose their strength completely.Mechanisms:(i) Intrinsic Breakdown(ii) Electromechanical Breakdown(iii) Breakdown Due to Treeing and Tracking(iv) Thermal Breakdown(v) Electrochemical Breakdown

Intrinsic breakdown: If the material under test is pure and homogeneous, the temperature and environmental conditions are carefully controlled, and the

sample is so stressed that there are no external discharges. With under voltages applied for a short time the electric strength increases up to an upper limit which is called the intrinsic electric strength.

The intrinsic breakdown is accomplished in times of the order of 10-8 sec. and has therefore been postulated to be electronic in nature. The stresses required for an intrinsic breakdown are well in excess of 106 volt/cm.

Streamer breakdown: An electron entering the conduction band of the dielectric at the cathode will drift towards the anode under the influence of the field

gaining energy between collisions and loosing it on collisions. On occasions the free path may be long enough for the energy gain to exceed the lattice ionization energy and additional electron is produced on collision. The process is repeated and may lead to formation of an electron avalanche similar to gases.

Electromechanical breakdown: Substances which can deform appreciably without fracture may collapse when the electrostatic compression forces on the test specimen

exceeds its mechanical compressive strength. The compression force arises from the electrostatic attraction between surface charges which appear when the voltage is applied. The pressure exerted when the reaches about 106 volt/cm may be several KN/m2. This breakdown due to mechanical stresses is called electromechanical breakdown.

Thermal breakdown: When insulation is stressed because of conduction currents and dielectric losses due to polarization, heat is continuously generated

within the dielectric. In general conductivity increases with temperature, conditions of instability are reached when the rate of heating exceeds the rate of cooling and the specimen may undergo thermal breakdown.

Breakdown due to internal discharges: Solid insulating materials, and to a lesser extent liquid dielectrics contains voids or cavities within the medium or at the boundaries

between the dielectric and the electrodes. These voids are generally filled with a medium of lower dielectric strength, and the dielectric constant of the medium in the voids is lower than that of the insulation. Hence the electric field strength in the voids is higher than that across the dielectric. Therefore even under normal working voltages the field in the voids may exceed their breakdown value, and breakdown may occur.

Breakdown of solid insulating materials:

Solid insulator Thickness(mm) Breakdown Voltage (KV)

Dielectric strength(KV/mm

)

Plastic sheet 2 25 13

Rubber sheet 3 35 11.57

Winding paper 0.1 26 26

Glass sheet 3 20 6.66

BREAKDOWN IN LIQUID DIELECTRICS Liquid dielectrics are used for filling transformers, circuit breakers and as impregnants in high voltage cables and capacitors.

For transformer, the liquid dielectric is used both for providing insulation between the live parts of the transformer and the grounded parts besides carrying out the heat from the transformer to the atmosphere thus providing cooling effect. For circuit breaker, again besides providing insulation between the live parts and the grounded parts, the liquid dielectric is used to quench the arc developed between the breaker contacts.

The liquid dielectrics mostly used are petroleum oils. Other oils used are synthetic hydrocarbons and halogenated hydrocarbons and for very high temperature applications sillicone oils and fluorinated hyrocarbons are also used.

The three most important properties of liquid dielectric are The dielectric strength The dielectric constant and The electrical conductivity.

Other important properties are viscosity, thermal stability, specific gravity, flash point etc. Transformer oil is the most commonly used liquid in power apparatus. It is almost colourless liquid Consisting of mixture of

H-C which include parafinns ,isoparafinns,nepthalin,aromatic which is service the liq. In T/F is subjected to prolong heating process with there time the oil darken due to the formation of the acid and resin of sludge in the liquid. Some of the acid are corrosive the solid insulator material and metal part in the transformer liquid dielectric normally are the mixture of hydrocarbons and normally weakly polarised when used for electrical insulator purpose. They should be free from mixture.

Presence of water in oil effect the electrical strength. Presence of water 0.01% reduces the electrical strength about 20 %.

switch on the apparatus. The system is micro-processor based and its take the reading of breakdown and calculate its

average. The printed result came out from the system. Now start the manual mode and repeat it. System take reading.

OBSERVATION TABLE:

Sr no. Sample 1(KV) Sample 2(KV) Sample (KV) Sample 4(KV)

1 57.8 33.8 49.2 21.7

2 84.7 35.7 52.5 26.6

3 66.9 31.0 58.4 26.5

4 92.2 42.0 67.6 35.1

5 91.2 51.7 54.4 48.0

6 83.3 48.3 60.7 40.7

average 79.3 41.4 57.1 33.1

Flash point: The flash point of volatile material is the lowest temperature at which it can vapourised to form an mixture in air. Measuring a flash point require a inition source. At the flash point the vapour may cease to burn when the source of igination

is removed. Flash point is indepdent to the temperature. The flash point is offten use as a discrutive characterstics of liquid fuel. And it also use to help characterise the fire hazzard of

liquid.

Interfacial tension Interfacial tension is the force that hold the surface of a particular phase together and normally measured

in dynes/cm or N/m. the surface tension between gas crude oil ranges from 0 to 34 dynes/cm. it is function of temperature and pressure.

The molecules at the surface of both of these liquids experience unbalanced forces of attraction. These unbalanced forces at the surface of separation between the two immiscible liquids (i.e., at the interface) give rise to interfacial tension. It can be defined in the same way as the surface tension.

CONCLUSION

In this report, we conclude that the transformer is very critical and expensive Equipment. So various tests are used to protect the transformer from damage. Here we included the introduction of transformer, its faults location, causes and diagnosis. In this report we did Domino on-line test, Breakdown Voltage test, Solid Insulation test, Oil Insulation test, Insulation Analyzer test, Flash point test, Interfacial test, Dissolved Gas Analysis, Sweep Frequency Response test, Thermal images camera and include their result. We should successfully did all the practical’s and find out how to use them. In this report all the test contain their introduction, procedure, sub instruments and result. We should easily understand how to use the instrument for transformer protection and use it for long period.

 

Thank You