Basic_Electrical_Engineering_4th_edition

In recent years, however, as a result of energy crisis in the world, it has been decided to investigate all possible means ofdeveloping power, as alternatives to fuelfired plants. The wind could supply a significant portion of the world's energy demand. An estimate by an American Professor indicates the potentialities ofwind power. According to him about 350,000 wind mills eachratedfor about 1250 KW to 2200 KWcould develop power ofthe order of190,000 MW. With the advancement in the knowledge ofaero-dynamics it has been possible to build larger and more efficient wind power plants. Atypical example is the 1250 KWinstallation at Grandpa's Knol in U.S.A. Whereas some success hasbeen achievedindeveloping small and medium size plants, the prospects oflarge scale generation i.e. 1 MW or above are not, as yet very encouraging.

Economic development ofwindpowerrequires selectionofsiteswherehighspecificoutputs are compatible with reasonable cost ofconstruction ofplant. It is, therefore, necessary to obtain wind velocity duration curve for a particular site and to know the output of the machine for varying wind velocities. The maximum efficiency ofthe wind power plant is found not to exceed

40%.

The windpowerplants canbe operatedincombinationwith steam or hydro power station, which will lead to saving in fuel and increase in firm capacity, respectively of these plants.

Windenergycanprove to be a potentialsource ofenergyforsolvingthe energyproblem. It can certainly go a long way to supply pollution-free energy to millions of people, living in the villages all over the world.

The economic viability ofwind mills is better in situations where conventional transmis­ sion costs are extremely high (because of inaccessibility and small load) or where continuous availability of supply is not essential so that only a limited amount ofstorage or standby power needbe provided.

10.5.3 Geothermal Power

Many geothermal power plants are operating throughoutthe world. Although larger geothermal power plants are in operation in America today, it is to the credit of the Italians that the first impressive breakthrough ingeothermalpower exploitation was achieved. The oldest geothermal powerstationis nearLarderelloinItaly, whichhas aninstalledcapacityof380 MW. InNewzealand geothermal power accounts for 40% ofthe total installed capacity, whereas in Italy it accounts for 6%.

It is a common knowledge that the earth's interior is made ofa hot fluid called 'magma'. The outer crust ofthe earth has an average thickness of 32 Km and below that, is the magma. The averageincrease intemperature with depthoftheearthis 1°C forevery 35 to 40 metre depth. At a depthof3 to 4 Kms, waterboils up and at a depth ofabout 15 Kms, the temperature is, inthe range of 1000° to 1200°C. Ifthe magmafinds its waythrough the weak spots ofthe earth's crust, it results into a volcano. At times, due to certain reasons the surface water penetrates into the crust, where it turns into steam, due to intense heat, and comes out in the form of springs or geysers. Moreover, the molten magma also contains water, whichit releases inthe form ofsteam, whichcould beutilizedfor electric power generation.

Combined Operation of Geothermal Plant

It is well knownthat a composite power system canbe supplied more economicallyby a combina­ tion oftwo main types ofplants :

(i) Base Load Plant which is characterised by high fixed cost and low variable cost.

(ii) Peak Load Plantwhich is characterised by low fixed cost and high variable cost.

Incase ofa geothermalplant,the usualpractice is to regard alltheproductioncost as fixed cost, with zero variable cost as no fuel is required for its operation. This is justified by the fact, that once geothermal steam has been made available by means ofcapital spent on exploitation, drillingand pipe work, it maybe regarded as free. Geothermal plants are, therefore, ideallyrated as base loadplants. Mostoftheplantstoday arebeingused asbase loadplants as theycan achieve annual plant load factor of 90% or more-higher than that obtainable from thermal or nuclear plant.

The commercialviabilityofgeothermalpower plant as compared to othersources, depends upon the cost ofalternative power sources and otherlocal factors. As a rule ofthumb, the follow­ ing guidelines may be followed to assess its viability :

(i)The fluid temperature at the bottom ofthe bore should be at least 180°C.

(ii)Atemperature of180°C should be available at depths not exceeding 3 Kms.

(iii)The yield from a 24f cm bore should be a least 20 tons/hr of steam.

The following are some ofthe geothermal powerprojects inoperation :

At present geothermal energy makes a very small, but locally important, contribution to world energy requirements. This situation will not change unless important technological ad­ vancesare made. Environmentally, itisprobablytheleast objectionable form ofpower generation available at present, with, the exception ofhydroelectric methods.

10.5.4 Wave Power

Another source ofnon-conventional energygenerationisthewavepower.The majorproblemwith the wave power is that itis notconcentrated at a place. Ifmeans could be developed for collecting the energy in the wave, spread over a large surface area, and concentrating it into a relatively small volume, the prospects, would be considerablyimproved.

It has been observed that a typicalwave measures 2 to 3 metres in heightthroughoutthe year. The energyper square metre ofwave surface area is given as 112p ga2 where p is density of sea water,gis acceleration due to gravity anda is the amplitude ofthe wave. Inthe Atlantic, the wave period Tis around 9 s, and the averagevelocityofpropagationofwave is 14 mis. It has been observed that a power flow ofaround 70 KWfor every metre ofwave front, canbe obtained. This is a considerable amount of power, especially when we think of the availability of this power throughoutthe year. Ifthe lengthofthe coast line is, say 1200 Km, the power available is around 84 GW.

utilized in photosynthesis which is essential for sustenance oflife on earth. Man hastried, from time immemorial, to harness this infinite source of energy, but has been able to tap only a negligibly small fraction ofthis energy, till today.

Three broadcategories ofpossible large scale applications ofsolar power are :

(i)The heating and cooling ofresidential and commercial buildings;

(ii)The chemical and biologicalconversionoforganic materialtoliquid, solid and gaseous fuels; and

(iii)Conversionofsolar energy to electricity.

The use of solar energy for generation ofelectricity is costly as compared to conventional methods. However, due to scarcityoffuel, solar energywill certainly find a place in planning the national energyresources.

1 0.6 CONVENTIONAL SOURCES

10.6.1 Hydro Station

The water wheel, as developed in the early part of 19th century, played an important role in converting water power into mechanical power. With the invention ofsteam engines,the use of waterwheelbeganto decrease andlarger steam engines were developed. Steamenginespossessed the advantage ofmobility, allowingpowertobe produced, where it was required and also that of flexibilityinits application.

It was onlylater withthe discoveryofconversionofmechanical energyinto electric energy, and transmission ofelectric energy being the most efficient method oftransporting energyfrom one place to another, that water wheel was revived. The modern water turbine, is being built in single unit ofmore than 200 MW. Also, the concept ofmultipurpose project, in which the produc­ tion of power is included as one of several uses (flood control, navigation, irrigation, water for domestic andindustrial purpose, etc.), has led to the development ofsites which otherwise could notbe harnessedeconomicallyforpower alone. The capitalinvestmentperKWis muchhigherin case of hydro power as compared to thermal power. This is because in order to store water at sufficient head, it is essential to construct a dam which is a costly affair. However, the running cost ofhydro electric energy is much less as no fuel is used.

Water power differs fundamentally from thermal powerin thatit represents aninexhaust­ ible source ofenergy which is continually replenished by the direct agency ofthe Sun; whereas thermal power represents chemical energy whichhas been created and stored within the earth's crust duringpast geological ages. The use ofchemical energyis thus equivalent to the consump­ tion ofcapitalas thereplacement is not so easy. Another important difference betweenthetwois that whereas water power can be developed only where it is present in nature, thermal power (liquid or solidfuel) canbe transportedfor use from one place to another.

Classification of Hydro Plants

The hydro-power plants can be classified in terms of location and topographical features, the presence or absence ofstorage, the range ofthe operating head etc.

Classification based on Plant Capacity

10.6.2 Steam Power Plant

With the invention of steam engine for obtaining mechanical energy, the so-called non-conven­ tionalmethods i.e. wind, tidal, geothermal etc. were abandoned as the costinvolvedwashigh and also there was no flexibilityfortransportation ofthis form ofenergy. The development ofsteam turbines and then electric generator completely replaced the non-conventional methods. Fossil fuels became the main source ofenergy for quite sometime. The size ofthe thermal plants grew from a few KW to more than 1000 MW as of today. The concept of generating electrical energy using fossil fuel has changed completely, the concept oflocating the power plants near the load centres to locating nearthe fuelpithead. Super-thermal powerplants (plants with capacity 1000 MW or more) have come into existance. Ithas beenfoundmore economical in generalto generate electrical energy near the pithead rather than nearthe load centres, eventhough the energy has to be transported over the transmission lines, which involves a large percentage oftotal capital cost and transmission line losses. On the other hand by installing a plant near pithead saves the cost oftransportingthe coal etc. A400 MWcapacityplantrequires about 5000 to 6000 tons ofcoal everyday.

10.6.3 Nuclear Power Plants

Nuclearpowerindustryhas maderelativelyfaster growth ascomparedwith otherforms ofpower industries. The first power reactor was commissioned sometime in 1944 and by 1972 there were more than 100 nuclear power plants in the world, with the total capacity exceeding 30 GW. The rapid growth canbe associatedwiththefollowingcharacteristics ofthe materials used fornuclear power generation :

(i)Energy is releasedwithout using oxygen for combustion (fission).

(ii)Breedingofnuclearfuelis possible so thatweproduce almost same amountofnuclear fuel as is spent, withoutreduction ofpower output.

(iii)The weight offuel requiredfor generating a particular amount ofenergy is much less thanwhatis requiredin conventional methodsofgeneration.

Nuclear Fuel

Uranium is the fuel used in nuclear power plants. It is non-renewable and has two isotopes, U'- 235 about 0.7% and U-238, 99.3%. Materials fissionableby thermal or low speed neutrons are U- 233, U-235 and Pu-239 (plutonium).

As natural Uranium is available in abundance in Britain, most ofthe reactors are using natural Uranium, whereas United States ofAmerica are using enriched Uranium for most of their reactors. In India, RajasthanAtomic PowerPlant uses natural Uranium, whereas Tarapur Power Plant uses enriched Uranium. Ifnatural Uranium is used, the size ofthe plant is larger than when enriched uranium is used. It has been estimated that about 1.2 kg of Uranium pro­ duces 1 MW ofpower for one year.

10.6.4 The Gas Turbine Plant

The first gas turbine was used in 1939 for large central station service as a prime mover. Since then several stations have been in operation. These plants require less space for the same capac­ ity as compared to a steam plant, it provides more flexibility in design, and involves low initial cost.

2.Short-circuit ofwire i.e. between phase and neutral is avoided as the two are placed in different grooves.

3.Physical inspection ofwiring makes it simple to carry out any repair if required (by opening the capping).

4.PVC casing capping gives better look and is economical as compared to wood.

Disadvantages :

1.In case of a short-circuit, there is risk offire (use ofwood or PVC).

2.Normally not recommended for damp places.

1 1 .2.3 Toughened Rubber Sheath {TRS or CTS) or Batton Wiring

In this case the cables are carried on seasoned teak wood perfectly straight and well varnished teak wood batton ofthickness not less than 1 cm. The cables are fixed on the batton by means of tinned brass or aluminium link clips already fixed on the batton with small nails before laying cables. The battons are fixed to the walls by means ofgutties with countersink headed wooden screws. The screws are to be fixed on the batton at an interval of about 75 ems. The minimum width ofbatton is 13 mm for two wires. It is found suitable where acids and alkalies are stored. The various sizes ofbatton available are 13, 19, 25, 31, 38, 44 and 50 mm width. Depending upon the no. of cables to be run, a suitable size ofbatton should be used.

The main advantages and disadvantages ofthis wiring are :

1.Easy to instal and economical as compared to casing cappings or conduit wiring.

2.Easy to detect fault ifany and has good appearance.

3.Relatively goodlife span.

Disadvantages :

1.Not suitable if exposed to sun and rain or places where dampness exists.

2.Risk offire high.

CTS stands for Cab Type sheathed.

1 1 .2.4 Conduit Wiring

There are three types ofconduit wiring :

(a)Concealed conduit wiring

(b)Surface conduit wiring

(c)Flexible conduit wiring.

Concealed conduitwiring. Here the conduits are embedded along the wall in plaster at the time ofconstruction. The VIR or PVC cables are drawn into the conduits by means ofGI wire of 18 SWG. The conduit should be electrically and mechanically continuous and connected to earth at some suitable places using earth wire. This method of conduit wiring is preferred for domestic over other methods as it maintains the beauty ofthe house and no projected pipes are visible.

Surface conduit wiring. As the name suggests the conduit is spaced from the wall by means of small wooden spacers below the conduits along its length at regular intervals. This system is commonly used in industrial wiring but is not recommended for domestic wiring as it spoils the beauty ofthe house. The usual size ofthe conduit is 25 mm diameter for domestic wiring.