Tariff

 The rate at which electrical energy supplied to consumer is known as tariff.

Although tariff should include the total cost of producing and supplying electrical energy plus the profit, yet it can not be the same for all types of consumers. It is because the cost of producing electrical energy depends to a considerable extent upon the magnitude of electrical energy consumed by the users and his load conditions. Therefore.,in all fairness, due consideration has has to be given to different types of consumers (e. g., Insustrial, domestic and commercial) while fixing the tariff. This makes the problem of suitable rate making highly complicated.

Obejectives of tariff. Like other commodities, electrical energy is also sold at such a rate so that it not only returns to the cost but also reasonable profit. Therefore, a tariff should include the filling items :

(1).Recovery of cost of producing electrical energy at the power station

(2).Recovery of cost on capital investment in transmission and distribution systems.

(3).Recovery of cost operation and maintenance of supply of electrical energy e. g., metering equipments, billing etc.

(4).A suitable profit on the capital investment.

Desirable characteristics of a tariff 

A tariff must have the following desirable characteristics

(1)Proper return : The tariff should be such that such that it ensures the proper return from each consumer. In other words, the total energy receipts from the consumers must be equal to cost of producing and supplying electrical energy plus reasonable profit.This will enable the electric supply company to ensure continuous and reliable service to the consumers.

(2).Fairness :Tariff must be fairness so that different types of consumers are satisfied with rate of charge of electrical energy. This a big consumer should be charged at a lower rate than a smaller consumers. It is because increased energy consumption spread the fixed charges over the greater number of units, thus reducing the overall cost of producing electrical energy. Similarly, a consumer whole lead condition do no deviate much from the ideal (i.e., non variable) should be charged at lower rate than the one whose load condition changes appreciably from the ideal.

(3).Simplicity :The tariff should be simple so that any ordinary consumer can easily understand it. A complicated tariff may cause an opposition from the public which is generally distrust ful of supply companies.

(4). Reasonable profit : the profit element in the tariff should be reasonable. An electric supply company is a public utility company and generally enjoys the benefits of monopoly. Therefore, the investment is relatively safe due to non competition in the market,. This call for the profit to be restricted to 8%or so per annum

(5)Attractive :The tariff should be attractive so that a large no of consumer are encouraged to use electrical energy. Efforts should be made to fix the tariff in such a way so that consumers can pay easily.

Types of Tariff :

There are several types of tariff. However, the following are commonly used types of tariff :

1.Simple tariff. When there is a fixed rate per unit of energy consumed, it is called a simple tariff or uniform rate tariff.

In this types of tariff, the price of charged per unit is constant i.e., it dost not vary with increase or decrease in number of unit consumed. The consumption of electrical energy at the consumers terminal is recorded by means of energy meter. This is simplest of all tariff and is readily understood by the consumers. 

Disadvantages.

(1).There is no discrimination between different types of consumers since every consumer has to pay equitably for fixed charges.

(2). The cost per unit delivered is high

(3). It does not encourage the use of electricity.

2.Flat rate tariff. When different types of consumers are changed at different uniform per unit rates, it is compounded called a flat rate tariff. In this type of tariff, the consumers are grouped into different classes and each class of consumers is charged at a different uniform rate. For instance, the flat rate per kWh for lighting load 'may be 60paise, where may be slightly less (say55 paise per hour kwh) for power load. This different classes of consumers are made taking into account their diversity and load factors. The disadvantage of such a tariff is that it is more fair to different types of consumers and is quite simple calculations

Disadvantages.

(1). Since the flat rate tariff varies according to the way the supply is used separates meters are required for lighting load, power load etc. This makes the application of such a tariff expensive and complicated.

(2).A particular class of consumer is charged at the same rate irrespective of magnitude of energy consumed. However, a big consumer should be charged at a lower rate as in his case the fixed charges per unit are reduced. 

(3).Block rate tariff. When a given block of energy is charged at a specified rate and the succeeding block of energy are charged at progressively reduced rates, it is called a block rate tariff. 

 In block rate tariff, the energy energy consumption is divided into the blocks and price per unit is fixed in each block. The price per unit in the first block is highest mountain and it it progressively reduced for succeeding blocks of energy. For example, the first 30 units may be charged at the rate of 60 paise per unit, the next 25 units at the the rate of 55paise per unit and the remaining additional units may be charged at the rate of 30 paise per unit. 

The advantages of such a tariff is that consumer gets an incentive to consume more electrical energy. This increases the the load factor of system and hence the cost of generation is reduced. However, it's principal defect is that it lacks a measure of consumers demand. This type of tariff is being used for majority of residential and small commercial consumers. 

4.Two-part tariff. When the rate of electrical energy is charged on the basis of maximum demand of the consumer and the unit consumed, it is called a two part tariff. 

In two part tariff, the total charge to be made from the consumer is split into two components viz., fixed charges and running charges. The fixed charges depends upon the maximum demand of the consumer while the running charges depends upon the number of units consumed by the consumer. Thus the consumer is charged at the certain amount per kW of maximum demand plus a certain amount per kwh of energy consumed i. e., 

Total charges =Rs(b*kW+ckWh) 

b= charges per kW of maximum demand 

c= charge per kWh of energy consumed 

This type of tariff is mostly applicable to industrial consumers who have appreciable maximum demand. 

Advantages 

(1).It is easily understood by the consumers. 

(2). It recovers the fixed charges which depends upon the maximum demand of the the consumer but are independent of unit consumed. 

Disadvantages 

(1) The consumers has to pay fix charges irrespective of the fact whether he has consumed or not consumed the electrical energy. 

(2).There is always error in assessing the maximum demand of consumer. 

5.Maximum demand tariff. It is similar to two part tariff with the only difference that the maximum demand is actually measured by installing maximum demand meter in premises of consumers. This removes the the objection of two part tariff where the maximum demand is assessed merely on the basis of reteable value. This type of tariff is mostly applied to big consumers. However, it is not suitable for small consumers(e. g., residential consumer) 7 as a separate maximum demand meter is required. 

6.Power factor tariff. The tariff in which power factor of the consumers load is taken into considerations is known as power factor tariff. 

Insulating materials of Cables

  The satisfactory operation of a cable depends to great extent upon the the characteristics of insulation used. Therefore, the proper choice of insulating material for cable is of considerable importance. In general, the insulating material used in cable should have following properties.

(1).Higher insulation resistance to avoid the leakage current.

(2). High dielectric strength to avoid the electrical breakdown of the cable.

(3).High mechanical strength to withstand to mechanical handling of cables.

(4). Non hygroscopic i. e., it should not absorb moisture from air or soil. The moisture tends to decrease the insulation resistance and hastens the breakdown of cable. In case the insulating material is hygroscopic, it 'must be enclosed in a waterproof covering like lead shealth.

(5). Non. Inflammble.

(6).Low cost so as to make the underground system a viable proposition.

(7). Uneffected by acids and alkalies to avoid any chemicals action.

NO one insulating' materials possess all the above mentioned properties. Therefore, the type of insulating material to be used depends upon the purpose for which the cable is required and quality of insulation to be aimed at. The principal insulating material used in cables are rubber, vulcanised India rubber, impregnated paper, varnished cambric and polyvinyl chloride.

 

1. Rubber. Rubber may be obtained from milky sap of tropical trees or it may be produced from oil products. It has relative permittivity varying between between 2 and 3,directric strength is about 30kV/mm and resistivity of insulation is 10^17ohm cm. Although pure rubber has reasonably high insulating properties, it suffers from some major drawbacks viz., readily absorb moisture, maximum safe temperature is low (about 38 centigrade)., soft and liable to damage due to rough handling and ages when exposed to light. Therefore, pure rubber cannot be used as an insulating material.

 

2. Vulcanised India Rubber (V. I. R). It is prepared by mixing pure rubber with mineral matter such as zine oxide, red lead etc., and 3 to 5% of Sulphur. The compound so formed is rolled into thin sheets and cut into strips,. The rubber compound is then applied to the conductor and is heated to a temperature of about 150 centigrade. The Whole process is called vulcanisation and the product is obtained is known as vulcanised India rubber. Vulcanised India rubber has greater mechanical strength, durability and wear

resistant property than pure rubber. It main draw back is that Sulphur reacts quickly with copper and for this reason, cables using vir insulation have tinned copper conductor. The vir insulation is generally used for low and moderate voltage cables

3. Impregnated paper. It consist of chemically pulped paper made from wood chipings and impregnated with some compound such as paraffinic or napthenic material. This type of insulation has almost superseded the rubber insulation. It is because it has the advantages of low cost, low capacitance, high dielectric strength and high insulation resistance. The only disadvantage is that paper is hygroscopic and even it if is impregnated with suitable compound, it absorbs moisture and thus lowers the insulation resistance of cable. For this reason, paper insulated cables are always provided with some protective covering and are never left unsealed, if it is required to be left unused on the site during laying, it ends are temporarily covered with wax or tar.

Since the paper insulated cables have the tendency to absorb the 'moisture, they are used where the cable route has a few joints. For instance, they can profitably used for distribution at low voltages in congested areas where the joints are generally provided only at terminal apparatus. However, for small installation, where the length are small and the joints are required at the number of places, vir cables Will the cheaper and durable than paper insulated cables.

 

 

4. Varnished cambric. I it is a cotton cloth impregnated and coated with varnish,. This type of insulation is also known as empire tape. The cambric is lapped on on to the conductor in the form of tape and it's surfaces are coated with petroleum jelly compound to allow for the sliding of one turn over another as the cable is bent,. As the vernished cambric is hygroscopic, therefore, such cables are always provided with metallic shealt. Its dielectric is about 4kV/mm and permittivity is 2.5 to 3.8.

5. Polyvinyl chloride (PVC). 3503 This insulating 'material is a synthetic compound. It is obtained from polymerisation of acetylene and is in the form of white powder. For obtaining this material as a cable insulation, it is compounded with certain material known as plastifcizers which are liquid with high boiling point. The plastifcizers form a gell and renders the material plastic over the desired range of temperature.

Polyvinyl chloride has high insulation resistance, good dielectric strength and mechanical toughness over a wide range of temperatures. 

Electric Power system

 The conveyance of electric power from power station to consumers premises is known as electric supply system.

An electric consist of three principal components biz., the power station, transmission line and distribution system. Electric power produced at power stations which are located at the favorable places, generally quite away from consumers. It is then transmitted over large distances  to the load centres with the help of conductor known as transmission line, it is distributed to a large no of small and big consumers through a distribution network. 

The electric supply systems can be broadly classified into (1)d.c. or a.c. system

(2).Overhead or underground system. 

Now a days, 3 phase, 3 wire and a.c. system is universally adopted for generations and transmission  of electric power as an economical proposition. However, distribution of electric power is done by 3-phase, 4-wire and a.c. system. The underground system is more expensive than the overhead system. Therefore, in our country, overhead system is mostly adopted for transmission and distribution of electric power.

Typical a.c. Power supply scheme

The large network of conductors between the power station and the consumer can be broadly divided into two parts viz., transmission systems and distribution system. Each part can be further subdivided into two primary transmission and and secondary transmission and primary distribution and secondary distribution. Shows the layout of a typical a.c. Power supply scheme by a single line diagram. It may be noted that it is not necessary that all power scheme includes all the stages shown in the figure. For example, in a certain power scheme, there may be no secondary transmission and another case, the scheme may be so small that there is only distribution and the no transmission.

 

(1).  Generating station :Generating station represents the generating ststion where electric power is produced by 3 - phase alternators operating in parallel. The usual generation voltage is 11kV. For the economy in the transmission of electric power, the generation voltage (i.e., 11kV) is stepped upto 132 kV or more at the generating station with the help of 3-phase transformers. The transmission of electrical power at high voltages has several advantages including the Saving the conductor material and high transmission efficiency. It may appear advisable to use the highest possible voltage for transmission of electrical power to save conductor material and have other advantages. But there is limit to which this voltage can be increased. It is because increase in transmission voltage introduces insulation problem as well as cost of a switch gear and transformer equipment is increased. Therefore, the choice of proper transmission voltage is essentially a Question of economics. Generally the primary transmission is carried at 66kV,132kV,220kV or 400kV.

 

Under ground cables

 Electric power can be transmitted or distributed either by overhead system or by underground cables. The underground cables have several advantages such as less liable to damage though storm or lightning, low maintenance cost, less chances of fault, smaller voltage drop and better generation appearance. However, their major drawback is that they have greater installations cost and introduced insulation problem at high voltage compared with equivalent overhead system. For this reason, underground cables are employed where it is impractiable to use overhead lines. Such location may be thickly populated areas where 'municipal authorities prohibited over head lines for the reason of safety, or under plants and substation or where' maintenance condition do not permit the use of overhead construction.

 

The chief use of underground cables for many years has been for distribution of electric power in congested urban areas at comparatively low or moderate voltage s. However, recent improvements in the design and manufacture have led to development of cables suitable for use at high voltages. This has Mada it possible to employ under ground cables for transmission of electrical power for short or moderate distance. In this chapter, we shall focus our attention on the various aspect of underground cables and their increasing use in power system.

An underground cables essentially consist of one or 'more conductors covered with suitable insulation and surrounded by a protecting cover. 

Although several types of cables are available, the type of cables to be used will depend upon the working voltage and service requirement. In general, a cables' must fulfil the following necessary requirements.

(1). The conductor used in cables to should be tinned stranded copper or aluminum of high conductivity. Stranding is done so that conductor may become flexible and carry more current.

(2).the conductor should be such that the cable carries the desired load current without without overheating and causes voltage drop within permissible limits. 

(3)The cables must have proper thickness of insulation in order to give high degree of safety and reliability at the voltage for which it is designed.

(4).the cables must be provided with suitable mechanical protection so that it will be may withstand the rough use in laying it.

(5).The 'material used in the manufacture of cables should be such that there is complete chemical and physical stability through out.

Construction of Cables. 

Shows the general construction of conductor cables. The various parts are :

(1) Core of Conductors. The A Cables may have one or more than one core (conductor) 7 depending upon the type of service for which it is intended. For instance, the 3conductor of the cables shown. The conductors are made of tinned copper or aluminum and are usually stranded in order to provide flexibility to cable.

(2). Insulation. Each core or conductor is provided with a suitable thickness of insulation, the thickness of layer depending upon the voltage be withstood by the cables,. The commonly used material for insulation are impregnated paper, the varnished cambric or rubber mineral compound. 

(3) Metallic sheath.In order to protect the cables from moisture the gases or damaging liquids (acid or alkalies) of in the soil and atmosphere a metallic sheath of lead or aluminum is provided over the insulation. 

(4).Bedding. Over the metallic sheath is applied a layer of bedding which consist of a fibrous material like jute or hessian sheath tape. The purpose of bedding is to protect the metallic shealth against corossion and from mechanical injury due to armouring.

(5).Armouring. Over the bedding, armouring is provided which consist of one are two layers of galvanized steel wire or steel tape. It's purpose is to protect the cable from mechanical injury while laying it and during the course of handling. Armouring may not be done in the case of some cables.

(6).Serving. In order to protect armouring from atmospheric condition, a layer of fibrous materials like jute similar to bedding is provided over the armouring. This is known as serving. 

It may not be out of place to mention here that bedding, armouring and serving are only applied to cables for the protection of conductor insulation and to protect the metallic sheath from mechanical injury. 

CORONA

 When an alternating potential difference is applied across two conductors whose spacing is large as compared to diameters, there is no apparent change in the condition of atmospheric air surroundings the wires if applied voltage is low. However, when applied voltage exceeds a certain value, called critical disruptive voltage, the conductor are surrounded by a faint violet glow called corona.

The phenomenon of corona is accompanied by a hissing sound, production of ozone, powerless and radio interference. The

higher the voltage is raised, the larger and higher the luminous envelope becomes, and greater are the sound, the power loss and radio noise. If the applied voltage is increased to breakdown value, a flash over will occur between the conductors dude to breakdown of air insulation.

The phenomenon of violet glow, hissing noise, and production of ozone gas in an over head transmission line is known as corona. 

If the conductors are polished and smooth, the corona glow will be uniform throughout the length of conductors, otherwise the rough points will be brighter. With D. C voltage there is difference in the appearance of two wires. The positive wires has uniform glow about it, while the negative conductor has spotty glow. 

Theory of corona formation :

Some ionization is always present in air due to cosmic rays, the ultraviolet radiation and radioactivity. Therefore, under normal condition, the air around the conductors contain some ionized particles (i.e.,free electron and positive ions) and neutral malocules. When P. d is applied between the conductors, the potential gradient is setup in the air which will have a maximum at the conductor surfaces. Under the influence of potential gradient, the existing free electrons acquire greater velocities. The greater the applied voltage, the greater the potential gradient and more is the velocity of free electron.

Factors affecting the Corona :

The phenomenon of corona is affected by physical state of atmosphere as well as the condition of the line, the following are the factor upon which corona depends. 

(1).Atmosphere.

(2).Conductor size

(3).Spacing between the conductor

(4).line voltage 

Generation of electrical energy

electricalengineeringwebs.blogspot.com The conversion of energy available in different for in nature into electrical energy is known as  generation  of electrical energy.

Electrical energy is a manufactured commodity like clothing, furniture or tools. Just as the manufacture of a commodity involves the conversion of raw materials available in nature into the desired form, similarly electrical energy is produced from the form of energy available in the nature. However, electrical energy differs in one important respect, where as other commodities may be produced at well and consumed as needed, the electrical energy must be produced and transmitted to point of Use at the instant it is needed. Entire process takes only a fraction of second. This instantaneous production of electrical energy introduces technical and echnomical consideration unique to electrical power industry. Energy is available in various form from different natural sources such as pressure head of water, chemical energy of fuels, nuclear energy of radioactive substances etc. All these form of energy can be converted into electrical energy by the use of suitable arrangement. The arrangements essentially employs an alternator coupled to a primes mover. The prime mover is driven by energy obtained from various sources such as burning of fuels, pressure of water, force of wind etc. For example chemical energy of fuel(e. g., coal) can be used to produced steam at high temperature and pressure. The steam is fed to a prime move which may be steam engine or steam turbine. The turbine convert heat energy of steam into mechanical energy which is further converted into electrical energy by the alternator. Similarly, the other form of energy can be converted into electrical energy by employing suitable machinery and equipment.

 

The sources of energy are

1.the Sun

2.the wind 

3.the water

4.the Fuels

5.nuclear energy

 

1) The sun:  the sun in primary source of energy. The heat energy radiated by sun can be focused over a small area by means of reflectors. This heat can be used to raise steam and electrical engergy can be produced with the help of turbine alternator combination. 

2): The wind : this mathod can be used where wind flows for a considerable length of time. The wind energy is used to run the wind mill which drives a small generator. I order to obtain the electrical energy from a wind mill continously, the generator is arrange to charge the betteries 

 

3) Water: when water is stored at a suitable place. It possesses potential energy because of head created. This water energy can be converted into mechanical energy with the help of water turbine 

4)Fuels)The main sources of energy are fuels, viz., solid fuel as a coal, liquid fuel as an oil and gas fuel as a natural  gas 

5)Nuclear energy : To wards the end of second war, it was discovered that large amount of heat energy is liberated by fission of uranium and other fissionable materials, it is estimated that heat produced by one kg of nuclear fuel is equal to that produced by 4500 tonnes of coal.