High voltage engineering notes pdf

We provide the High Voltage Engineering lecture notes in pdf format to ease their accessibility and let the students get everything required for the preparations without any hassles. Apart from the explanations of the topics and concepts, the notes and reference books also contain real-life applications and described examples of the topics to help the students prepare well.

Further, to help them get the best practice, many solved, and unsolved questions are also available in the materials. High Voltage Engineering is an important branch of electrical engineering and is important for the education of electrical engineering graduation and post-graduation. This subject contains the study of electrical phenomena that occurs in various mediums at some higher voltages.

High voltage ensures more efficiency and lower loss. This is an important subject for the career of the electrical engineers as they will many times have to deal with certain similar situations in their future jobs. The notes are available for free pdf download format, ensuring that the students do not have to face any hassles while accessing them, and can directly take reference from these anytime they wish to do so.

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These pdf format study materials are easily available on the website, making sure that the students can access them anytime and will never have to compromise on education ever. Along with the study materials and the lecture notes, it is also important for the students to learn from the reference books to have an enhanced understanding of the concepts. These reference books come from some certified experts of the topics and chapters, who are well-known is the said fields for their works.

The reference books available for High Voltage Engineering also contains the related and advanced concepts, along with more examples and questions, that might be absent from the lecture notes due to their irrelevancy from the university and institute-level syllabus. These materials will help those students who want to have every detail about the topic, whether or not relevant to the syllabus.

After thorough research, we came up with the best reference books for High Voltage Engineering that are available in the global markets. All of these books are the best ones. However, the students can choose the right one suiting their needs. High Voltage Engineering is a large topic with wider coverage, containing many basic and advanced level concepts, interrelated to each other.

These reference books come from some certified experts of the topics and chapters, who are well-known is the said fields for their works. The reference books available for High Voltage Engineering also contains the related and advanced concepts, along with more examples and questions, that might be absent from the lecture notes due to their irrelevancy from the university and institute-level syllabus.

These materials will help those students who want to have every detail about the topic, whether or not relevant to the syllabus. After thorough research, we came up with the best reference books for High Voltage Engineering that are available in the global markets.

All of these books are the best ones. However, the students can choose the right one suiting their needs. High Voltage Engineering is a large topic with wider coverage, containing many basic and advanced level concepts, interrelated to each other. The High Voltage Engineering curriculum or syllabus contains a detailed description of all the involved topics and the sequence that one must follow for learning the subject. Having the syllabus of High Voltage Engineering handy will ensure that the students will have the correct details about the topics to be covered and what sequence to be followed for understanding every concept well and getting the best outcomes.

The syllabus also contains the basic and advanced topics, all added in the right manner. Furthermore, for every wider topic, all the subtopics are also present in the syllabus to help the students get a better idea.

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Apart from learning from the certified notes and reference books, it is also important to practice the important questions of any subject to have the best practice and preparation for it. Here is a list of top important questions of High Voltage Engineering:.

Answer: High Voltage Engineering is a vital subject in electrical engineering and is taught to graduation and post-graduation students in their education. It is the study of electrical phenomena taking place in several mediums under the action of higher voltages. Use of high voltage is more effective and ensures a lower loss. It provides a better line transmission capacity and extends the power value of the transmission for longer distances. High Voltage Engineering deals mainly with planning, organizing and testing of the electrical devices using higher voltage for ensuring reliable operations for the power network.

Answer: Taking reference from the expert-designed High Voltage Engineering lecture notes provides a brief about all the basic and advanced concepts of the subject. Some of the electrons dashing against the anode with sufficient energy shall break the chemical bonds of the insulation surface. Similarly, positive ions bombarding against the cathode may increase the surface temperature and produce local thermal instability.

Similarly, chemical degra-dation may also occur ll from the active discharge products e. The net effect of all these processes is a slow erosion of the material and a consequent reduction in the thickness of the specimen. Normally, it is A desired that with ageing, the dielectric strength of the specimen should not decrease. This is the main reason why high a.

In ld fact, these days very low frequency testing is being suggested 0. The breakdown of solid dielectric due to internal discharges or partial discharges has been elaborately explained in section 6. High insulation resistance 2. High dielectric strength W 3. Good mechanical properties i. It should not be affected by chemicals around it 5.

It should be non-hygroscopic because the dielectric strength of any material goes very much down with moisture content Vulcanized rubber : Rubber in its natural form is highly insulating but it absorbs moisture readily and gets oxidized into a resinous material; thereby it loses insulating properties. When it is mixed with TU sulphur alongwith other carefully chosen ingredients and is subjected to a particular temperature it changes into vulcanized rubber which does not absorb moisture and has better insulating properties than even the pure rubber.

It is elastic and resilient. The electrical properties expected of rubber insulation are high breakdown strength and high insulation resistance. In fact the insulation strength of the vulcanized rubber is so good that for lower voltages the radial thickness is limited due to mechanical consideration.

The physical properties expected of rubber insulation are that the cable should withstand nor- JN mal hazards of installation and it should give trouble-free service. Vulcanized rubber insulated cables are used for wiring of houses, buildings and factories for low-power work. There are two main groups of synthetic rubber material : i general purpose synthetics which have rubber-like properties and ii special purpose synthetics which have better properties than the rubber e.

The four main types are: i butyl rubber, ii silicon rubber, iii neoprene, and iv styrene rubber. Butyl rubber compound can be so manufactured that it has low water absorption and offers interesting possibilities for a non-metallic sheathed cable suitable for direct burial in the ground.

Silicone rubber: It is a mechanically weak material and needs external protection but it has high heat resistant properties. The raw materials used for the silicon rubber are sand, marsh gas, salt, coke and magnesium. Neoprene: Neoprene is a polymerized chlorobutadiene. Chlorobutadiene is a colourless liquid ld which is polymerized into a solid varying from a pale yellow to a darkish brown colour.

Neoprene does not have good insulating properties and is used upto V a. Styrene rubber: Styrene is used both for insulating and sheathing of cables. It has properties almost equal to the natural rubber. For use in cable industry the polymer must be compounded with a plasticizer which makes it plastic over a wide range of temperature.

The grade of PVC depends upon the plasticizer. PVC is inferior to vulcanized in respect of elasticity and insulation W resistance. PVC material has many grades. General purpose type: It is used both for sheathing and as an insulating material. In this com- pound monomeric plasticizers are used. It is to be noted that a V. Hard grade PVC: These are manufactured with less amount of plasticizer as compared with general purpose type. Hard grade PVC are used for higher temperatures for short duration of time like TU in soldering and are better than the general purpose type.

Hard grade can not be used for low continu- ous temperatures. PVC compounds are normally costlier than the rubber compounds and the polymeric plasticized compounds are more expensive than the monomeric plasticized ones. PVC is inert to JN oxygen, oils, alkalis and acids and, therefore, if the environmental conditions are such that these things are present in the atmosphere, PVC is more useful than rubber.

Polythene This material can be used for high frequency cables. This has been used to a limited extent for power cables also. The thermal dissipation properties are better than those of impregnated paper and the impulse strength compares favourably with an impregnated paper-insulated device.

Cross-linked polythene: The use of polythene for cables has been limited by its low melting point. The polythene is inert to chemical reactions as it does not have double bonds and polar groups. Therefore, it was thought that polythene could be cross-linked only through special condition, e. Many irradiation processes have been ld developed in the cable making industry even though large amounts of high energy radiations are required and the procedure is expensive. Polythene can also be irradiated with ultraviolet light, after adding to it a smal quantity of ultra- violet sensitive material such as benzophenone.

Under the influence of ultraviolet light on benzophenone, a radical is formed of the same type as in the decomposition of peroxide by the radical or mechanism. Organic peroxides have also been used successfully to crosslink the polythene.

Impregnated paper A suitable layer of the paper is lapped on the conductor depending upon the operating voltage. It is then dried by the combined application of heat and vacuum.

This is carried out in a hermetically sealed steam heated chamber. After the W device is dried, an insulating compound having the same temperature as that of the chamber is forced into the chamber. All the pores of the paper are completely filled with this compound. After impregna- tion the device is allowed to cool under the compound so that the void formation due to compound shrinkage is minimized.

In case of pre-impregnated type the papers are dried and impregnated before they are applied on the conductor. The compound used in case of impregnated paper is a semifluid and when the cables are laid TU on gradients the fluid tends to move from higher to lower gradient.

This reduces the compound content at higher gradients and may result in void formation at higher gradients. This is very serious for cables operating at voltages higher than 3. In many cases, the failures of the cables have been due to the void formation at the higher levels or due to the bursting of the sheath at the lower levels because of the excessive internal pressure of the head of compound. Insulating press boards. If the thickness of paper is 0.

When many layers of paper are laminated with an adhesive to get desired thickness, these are known JN as press boards and are used in bushings, transformers as insulating barriers or supporting materials.

The electrical properties of press boards varies depending upon the resin content. The application of these press boards depends upon the thickness and density of paper used. For high frequency 3 capacitors and cables usually low density paper 0. The electric strength of press board is higher than that of resins or porcelain. Mica consists of crystalline mineral silicates of alumina and potash. It has high dielectric strength, low dielectric losses and good mechanical strength.

Thin layers of mica are laminated with a suitable resin or varnish to make thick sheets of mica. Mica can be mixed with the required type of resin to obtain its application at different operating temperatures.

Mica is used as a filler in insulating materials to im- prove their dielectric strength, reduce dielectric loss and improve heat resistance property. Ceramics materials are produced from clay containing aluminium oxide and other inorganic materials. The breakdown strength of porecelain compared to other insulating material is low but it remains unaffected over a wide range of temperature variation. Porcelain is chemically insert to alkalies and acids and, therefore, corrosion resistant and does not get contaminated.

Alumina Al2O3 has replaced W quartz because of its better thermal conductivity, insulating property and mechanical strength. It is used for the fabrication of high current vacuum circuit breakers. Glass is a thermoplastic inorganic material consisting of silicondioxide SiO2 , which is available in nature in the form of quartz.

Different types of metal oxides could be used for producing different types of glasses but for use in electrical engineering only non-alkaline glasses are suitable having alkaline content less than 0.

The dielectric constant of glass varies between 3. Glass is used for X-ray equipments, electronic valves, electric bulbs etc. Epoxy Resins. Epoxy resins are low molecular but soluble thermosetting plastics which exhibit sufficient hardening quality in their molecules. The chemical cross-linking of epoxy resins is normally carried out at room temperatures either by a catalytic mechanism or by bridging across epoxy molecule through the epoxy or hydroxyl group.

JN Epoxy resins have high dielectric and mechanical strength. They can be cast into desired shapes even at room temperature. They are highly elastic and it is found that when it is subjected to a pressure of psi, it returned to its original shape after the load is removed. The dielectric constant varies between 2. These are found to be more compatible to the decomposed products of SF6 by partial discharge and arcing discharges.

It is to be noted that the cast or encapsulation should not contain voids or humidity especially in high voltage applications and the material is desired to be homogeneous. It is, therefore, desirable to dry and degas the individual components of the mixture and casting is preferably carried out in vacuum. The epoxy resins casts are inert to ether, alcohol and benzol. It is for this reason that they are not found suitable for applications in filled transformers.

There are certain application which require insulating materials to operate between a high range of temperature e. Some of the applications are space shuttle solar arrays, capaci- tors, transformers high speed locomotive, microprocessor chip carriers, cryogenic cables and other or applications at cryogenic temperatures.

For this some thermoplastic polymer films are used which have unique combination of electrical, mechanical and physical quantities and these materials are able to retain these properties over a wide range of temperatures where other insulating materials may fail. These films are used under extreme W conditions of temperature and environment.

These films are used for insulation on high temperature wires, cables, motor coils phase and ground insulation and for capacitors. This is also used as a substrate for flexible printed circuits and flexible cables. Another insulating film in which has the best thermal properties in this category of insulating materials is polyimide film under the trade name of Kapton manufactured by DuPont of America.

It has high dielectric and tensile strength. The TU disadvantages of the film are i high moisture absorption rate and ii it is affected by alkalies and strong inorganic acids. Kepton films can be used capacitors, transformers formed coil insulation, motor state insulation and flexible printed circuits. The film is selectively costlier and is mainly used where its unique charac-teristics makes it the only suitable insulation. The use of this insulation for motors reduces the overall dimensions of the motors for the same ratings.

It is, therefore, used in almost all situations JN whose space is a serious problem and the other nature insulation result in bigger dimension. Another recently developed resins is poly carbonate PC which is good heat resistant; it is flexible and has good dielectric characteristic. It is not affected by oils, fats and dilute acids but is adversely affected by alkalies, esters and aromatic hydrocarbons. The film being cost effective and fast resistant, it is used for coil insulation, slot insulation for motors and for capacitor insulation.

This is known as the lexon polymer. General Electric Co. It is used as insula-tion for transformers and motors. These also carry out heat from the windings of the electrical equipments. However, solid insulating materials are used only to provide insulation only. International Electrotechincal Commission has categories various insulating materials depend- ing upon the temperature of operations of the equipments under the following categories. While describing the dielectric and other properties of various insulating materials, their appli- W cation for various electrical apparatus has also been mentioned in the previous paragraphs.

However, a reverse process i. Power Transformers. For small rating, the coils are made of super-enamelled copper wire. For layer to layer, coil to coil and coil to ground iron core craft paper is used. However, for large size transformers paper or glass tape is rapped on the rectangular TU conductors whereas for coil to coil or coil to ground, insulation is provided using thick radial spacers made of press board or glas fibre. In oil-filled transformers, the transformer oil is the main insulation.

However between various layers of low voltage and high voltage winding oil-impregnated press boards are placed. SF6 gas insulated power transformers make use of sheet aluminium conductors for windings and turn to turn insulation is provided by a polymer film. The transformer has annular cooling ducts through which SF6 gas circulates for cooling the winding. SF6 gas provides insulations to all major JN gaps in the transformer. This transformer is used where oil filled transform is not suitable e.

The terminal bushings of large size power transformer are made of condenser type bushing. The terminal itself consists of a brass rod or tube which is wound with alternate layers of treated paper and tin foil, so proportioned, as to length, that the series of condensers formed by the tin foil cylinders and the intervening insulation have equal capacitances, thereby the dielectric stress is distributed uniformly. Circuit Breakers.

The basic construction of any circuit breaker requires the separation of con- ll tacts in an insulating fluid which serves two functions here: i It extinguishes the arc drawn between the contacts when the CB, opens.

The insulating fluids commonly used for circuit breakers are i Air at atmospheric pressure: Air break circuit breaker upto 11 kV. The controlled break and minimum oil circuit breakers enclose the breaker contacts in an or arcing chamber made of insulating materials such as glassfibre reinforced synthetic resins etc.

Rotating Machines. For low voltage a. For high voltage and large power capacity machines, the space limitations demand the use of insulating materials having substantially greater dielectric strength. Mica is considered to be a good choice not only due to space requirements but because of its ability to withstand higher temperatures.

W However, the brittleness of mica makes it necessary to build up the required thickness by using thin flakes cemented together by varnish or bakelite generally with a backing of thin paper or cloth and then baking it under pressure. Epoxy resin bounded mica paper is widely used for both low and high voltage machines. Multilayer slot insulation is made of press board and polyester film. However, for machines with high operating temperatures kapton polymide is used for slot insulation.

Mica has always been used for stator insulations. In addition to mica, conducting non-woven polyesters are used for corona protection both inside and at the edges of the slots. Glass fibre reinforced epoxy wedge TU profiles are used to provide support between the winding bars, slots and the core laminations. Power Cables. The various insulating materials used are vulcanised rubber, PVC, Polyethylene and impregnated papers.

Vulcanised rubber, insulated cables are used for wiring of houses, buildings and factories for low power work. PVC is inert to oxygen, oils, alkalies and acids and therefore, if the environmental conditions are such that these things are present in the atmosphere, PVC is more useful than rubber. JN Polyethylene is used for high frequency cables. The thermal dissipation properties are better than those of impregnated poper.

In case of impregnated paper, a suitable layer of the paper is lapped on the conductor depending upon the operating voltage. The compound used in case of impregnated paper is semifluid and when the cables are laid on gradients the fluid tends to move from higher to lower gradients which reduces the compound content at higher gradients and may result in void formation at higher gradients.

For this reason, impregnated paper cables are used upto 3. Because of the good thermal characteristics and high dielectric strength of the gas SF 6, it is used for insulating the cables also. SF6 gas insulated cables can be matched to overhead lines and can be operated corresponding to their surge impedance loading.

Power Capacitors. Capacitor design economics suggests the use of individual unit assembled in appropriate series and parallel connected groups to obtain the desired bank voltage and reactive ld power ratings both in shunt and series capacitor equipments. Series capacitor duty usually requires that a unit designated for a series application be more conservatively rated than a shunt unit.

However, there is no basic difference in the construction of the two capacitors. The most commonly used capacitor for the purpose is the impregnated paper capacitor. This consists of a pair of aluminium foil electrodes separated by a number of Kraft paper tissues which are or impregnated with chlorinated diphenyl and has a higher permittivity and results in reduction in the quantity of materials required for a given capacitance and the cost.

Because of imperfection involved in the manufacturing process of the dielectric paper it is desirable to use at least two layers of tissues between metal foils so that the possibility of W coincidence of weak spots is avoided. The effective relative permittivity depends upon the paper and the impregnant. For chlorinated diphenyl impregnant the relative permittivity lies between 5 and 6.

Normally through past experience, the area of the plate for a particular material of paper and impregnant per microfarad of capacitance is known and hence it is possible to obtain the number of turns of paper to be wound on a given diameter of mandrel for a specified foil width and for the particular lay-up of foil and paper.

The method of laying up the paper and metallic foil and the connection of lugs is shown in Fig. Two layers of dielectric are used as without it rolling would short circuit the plates. As a result of this, two capacitors in parallel are formed by the roll.

The foil and the paper interleaved in this fashion are wound on to a mandrel which is split to allow easy removal of the finished roll. If the section of the container is same as that of the roll, minimum overall value for the capacitor is obtained. As a result of this, quantity of free impregnant is a minimum thereby the risk of leakage of impregnant with variation in temperature is reduced.

Sometimes a high resistance for discharge is connected across the termi-nals of the capacitor for safety reasons. JN Terminal tapes ll Foils Fig. Further advances in the manufacture of dielectric materials led to single unit of kVAr even ld though the rating of a single unit based on economy ranges between and kVAr. Replacement of askarel with non-PCB fluids did not have much effect on unit sizes or ratings.

The newer all polypropylene film dielectric units offer distinct advantages in reduced losses and probability of case rapture as well as improvement in unit ratings. The large size units have made it possible to reduce the physical equip-ment size and the site area requirements.

The average price of smaller units in terms of kVAr is Rs. It is to be noted that aluminium foil are used in these capacitors as it has high thermal and electrical conductivity, has high tensile strength, high melting point, is light in weight, low cost and is easily available.

W Capacitor Bushings. Capacitor bushing is used for the terminals of high voltage transformers and switch gears. The power conductor is insulated from the flange by a capacitor bushing consisting of some dielectric material with metal foils cylinderical sheaths of different lengths and radii embedded in it as shown in Fig.

If these capacitor have the same capacitance, the potential difference between their plates will be equal. The equal capacitance between different layers is made possible by choosing suitable axial length together ld R2 with ratio. With this strategy the potential gradient in the dielectric is uniform but the edges of the R 1 foil sheets lie on a curve, thus giving unequal surfaces of dielectric between the edges of successive sheets.

How- or ever, if the differences between the lengths of successive sheets are made equal, the radial stress is not uniform and hence a compromise between the two conditions is usually adopted. There are three types of papers used as insulating materials for capacitor bushings; oil impreg- nated paper, resin bonded paper and resin impregnated paper. The oil impregnated paper bushing is made by wrapping untreated paper after inserting foil sheets at the appropriate position and then im- W pregnating with transformer oil after vacuum drying.

Before impregnation, it is ensured that moisture and air voids are avoided. In case of resin impregnated bushing creped paper tape is wrapped round the conductor and then dried in an autoclave under controlled heat and vacuum. Epoxyresin is then sprayed to fill the winding.

In case of resin bonded paper bushing, the paper is first coated with epoxyresin and wrapped round a cylinderical form under heat and pressure after inserting foil sheets at appropriate position. One mm of Hg pressure is also known as one torr after the name of Torricelli who was the first to obtain pressures below atmosphere, with the help of mercury barometer.

Sometimes JN —3 —8 10 torr is known as one micron. It is now possible to obtain pressures as low as 10 torr.

In a Townsend type of discharge, in a gas, the mean free path of the particles is small and electrons get multiplied due to various ionization processes and an electron avalanche is formed. In a vacuum of the —5 order of 10 torr, the mean free path is of the order of few metres and thus when the electrodes are separated by a few mm an electron crosses the gap without any collision.

Therefore, in a vacuum, the current growth prior to breakdown can not take place due to formation of electron ava-lanches. However, if it could be possible to liberate gas in the vacuum by some means, the discharge could take place according ll to Townsend process. Thus, a vacuum arc is different from the general class of low and high pressure arcs. Because of the large mean free path for the electrons, the dielectric strength of the vacuum is a thousand times more than when the gas is used as the interrupting medium.

In this range of vacuum, the breakdown strength is independent of the gas density and depends only on the gap length and upon the condition of electrode surface. Highly polished and thoroughly degassed electrodes show higher breakdown strength. Electrodes get roughened after use and thus the dielectric strength or breakdown strength decreases which can be improved by applying successive high voltage impulses which of course does not change the roughened surface but removes the loosely ld adhering metal particles from the electrodes which were deposited during arcing.

It has been observed —6 that for a vacuum of 10 torr, some of the metals like silver, bismuth-copper etc. This property of vacuum switches permits the use of short gaps for fast operation.

Cathode spots are formed depending upon the current flowing. For low currents a highly mobile cathode spot is formed and for large currents a multiple number of cathode spots are formed.

These spots constitute the main source of vapour in the arc. Natural causes for over voltages — Lightning phenomenon, Over voltage due to switching surges, system faults and other abnormal conditions, Principles of Insulation Coordination on High voltage and Extra High Voltage power systems.

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