BASIC
`ELECTRICAL
`ENGINEERING
`
`With Numerical Problems
`VOLUME I
`
`PS Dhogal
`
`Mitsuba - 1011
`Page 1 of 7
`
`

`

`Basic
`Electrical
`Engineering
`With Numerical Problems
`Volume I
`
`P S DHOCAl.
`Industrial Training hmitute
`Pusa, New Delhi
`
`Reviewtd by
`Mr. PC Singha!
`Heai:I, Electrical Engineering Depanmcnt, Aryabha1 Polytechnic:, Delhi
`
`Pt Pramod
`Assistant Training Officcrf Scnior Technical As.1is1ant, DGE&T. New Delhi
`
`Mr. Amrik Singh Wadan
`lnspec:1or. Food and Supplies, Amritsar
`
`. Tata.acGraw-HIII Publlshlng Company Umlted
`NEW DELHI
`
`Mitsuba - 1011
`Page 2 of 7
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`

`

`This book has been recom,nea4cd by the Directorate General of Employment
`and Training (DGE&T), N~ Qolbi,, vide-their circular No. DGET-14(2)/86-CD.
`dated April I. 1986.
`
`Volume II has been recommoack,d by the Directorate General of Employment
`and Training (DGE&T), Now Delhi. vide-their circular No. DGET-10(6).188.CD.
`dated November 22, 191&.
`
`0 1985. Tata McGraw-Hill Publishing Company Limited
`
`30• rq,riot 2006
`RAN RNQJ.aQQ
`
`No part of this publication can be reproduced in any form or by
`any means without the prior written permission of the publishers
`
`This edition can be exported from India only by the publishers,
`Tata McGraw-Hill Publishing Company Limited
`
`ISBN o-o7-451586-l
`
`Published by Tata McGraw-Hill Publishing Company Limited,
`7 West Patel Nagar, New Delhi 110, and printed at
`Ram Book Binding House, New Delhi 110 020.
`
`Mitsuba - 1011
`Page 3 of 7
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`Wires. Cebles end Accenorle,
`
`37
`
`them and the
`in
`very few free electrons
`interchange between atoms is little. Thercf(lre,
`in~ulators do not conduct any electric current
`or conduct very little if a very high potcnti 1i
`difference is applied across them.
`
`2.24 QUALITIES OF INSULATING MATERIALS
`The foll1>wing are the main qualities of good
`insulating materials which should be consider(cid:173)
`ed while selecting a particular one for use :
`(i) It should be flexible.
`(ii) Jt should have good mechanical s treng(cid:173)
`th .
`(ilfl It should be nonabsorptive of moisture.
`(fr) It should be easily moulded to any
`shape.
`(v) It should be noninflammable.
`(,•/) It should not be affected by acids or
`alkalies.
`(1'/i) It should have high specific resistana
`to reduce the possibilities of leakage
`It should be capable of
`current.
`working at high temperature because
`insula tors lose their insulating proper(cid:173)
`ties as the temperature increases.
`(,·iii) Jt should have high dielectric strength,
`i.t. the valµe of the voltage a t which
`the breakdown takes place in a plate
`of insulator I mm thick should be
`high. Dielectric strength of an insu(cid:173)
`lator is measured in kilovolts per
`millimetre thickness.
`
`The majority of insulating materials available
`for use in the construction of electrical machi·
`nes and apparatus have only a few of the
`aboye mentioned properties. It is, therefore,
`!he w~rlc of the designer to select a part icular
`1osulat1on for the purpose
`for which it is
`required.
`
`2.15 COMMON JNSULATINC MATERIALS-
`THEIR PR()PF.RTIES ANO USES
`The following a re the common
`insulators
`which are extensively used in electrical and
`electronic industries.
`
`Mica
`It is a very good insulator and
`is
`widely used as an insulating ma terial in elec·
`It has very
`trical and electronic industries.
`high specific resista nce and dielectric strength.
`It is fireproof and docs not absorb moisture.
`Mica is obtained from mines in big solid
`shee ts. Thin sheets can be obtained of thick-
`
`Fla, 2.20 Fae klt•kat
`
`are connected the incoming an~ o~tgoing
`cables of the live wire. The carrier is also
`made of porcelain and carries the fuse elemen!·
`The following are the main advantages of this
`design .
`(i) It facilitates easy renewal of the fuse
`wire and docs not involve any danger
`of coming in contact with it,
`(ii) It is very cheap to replace the fuse
`wire.
`. . . .
`f
`(iii) It docs not involve a ny poss1b1ht1es '?
`coming in contact with the metallic
`.
`~~ri~
`J t. however, suffers from unreliabl~ operatton
`owing to the use of ~n incorr~ct ~,z.e of the
`fuse wire and owmg to ox1da!1on. Tb~se
`fuses a re meant for low rupturing capacity
`a nd are not employed for th.c power circuit.
`
`Iron.Clad Cat..c,ut The general practice is
`not to use semi.enclosed fuse holders unless
`they are provided with a n iron cover. These
`fuse holders a re known as iron.clad cut•outs
`(Fig. 2.21).
`
`Fla. 2.21
`
`lroa·clad nH>0t
`
`2.23 lNSULA TOR
`A substance which (at a particular voltage)
`docs not allow the flow of elec trons (c urrent)
`insulator. For
`Ulrougb them is called an
`example, some of the good
`insulators are
`mica, porcelain, glass, rubbe r, Bakelite, etc.
`In insulators the electrons are closely and
`strongly bound to the nucleus. There arc
`
`Mitsuba - 1011
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`•
`
`Basic Eloctric.al Engineering
`
`ness O.OOOS i.i. On account of it being avail(cid:173)
`ahle in thin sheets. it can be rolled and used
`where the spa~ is limited. Mica starts soft(cid:173)
`ening at 1200°C. However, at 600°C it is
`very stable. Tbercf o re, it can be used as an
`insulating material where the temperature is
`not to increase beyond 600°C.
`Jn between
`600° and t 200°C mica starts disassociating.
`Therefore. it cannot be used at an insulator
`beyond 600°C. For
`temperatures above
`600°C it is mixed with shellac or a resin adhe(cid:173)
`sivdc nown as micanite, which can withstand
`higher temperature. A mixture o f mica and
`adhesive pasted o n paper or cloth is known
`as micaoite paper o r micanite cloth. Micaoite
`can be bent into a ny shape when it is heated.
`Mica is used as an insulator in electric irons,
`between commutator segments, slot
`linings
`fo r high voltage machines. condensers and
`for many other electrical and electronics work.
`
`Robber Rubber in tho pure form is very soft
`and to make it tough-and hard. 5% ulphur
`and other mineral materials. such as iinc
`oxide. red lead and some colour arc added to
`ft i
`it .
`then known as vulcanized rubber.
`It docs not absorb moisture up to a certain
`limit and serves as a good insulation and·
`protective covering fo r conduc tors for low
`It melts easily and
`and medium voltages.
`can be moulded into any shape. It is flexible,
`resistant to abrasion, chemicals a nd
`the
`It is inflammable but has
`affects of oxygen.
`low conductivity. Therefore, it is used as an
`insulating ma terial in various electrical appli(cid:173)
`ances, insulation on wires, rubber gloves.
`hard rubber battery containers, etc.
`
`PolyYiDyl ClalorWe (P. V .C .) It is a synthetic
`chemical substance which is used as a shea th(cid:173)
`ing on insulated cables or flexible cords to
`form an outer protective covering. This
`protective covering makes the cable re3.Soo(cid:173)
`ab~ resistant to decay, mechanical abrasion,
`acid alkalies and other corrosive materials.
`It has very·good insulating properties.and has
`now superseded the cab-type insulation of
`It can be moulded into any shape.
`the cable.
`Jt docs not
`It is Jlviilabte in many colours.
`absorb moisture and is unaffected by oil.
`grease a nd acid. P. V .C . has very good
`insulating properties and nowadays
`it
`is
`replacing rubber for cable iosulatiolf.
`
`Tropodare Jt is a hard. tough aod excellent
`insulation like P.V.C . and is not affected by
`theatmosphere. It does not easily get damag(cid:173)
`ed by mechanical injury. Jt is used on cables
`which arc subjected to work at damp places.
`chemical plants a nd oil factories. Tropodure
`is the trade mark for the thermoplastic com(cid:173)
`pound on a polyvinyl chloride. This insula(cid:173)
`tion is also employed on submarine cables.
`
`Eboalte or Vaku.ite It is a good insulator
`and can be moulded into any shape.
`It is
`manufactured by mixing 30 to 50% sulphur
`with vulcanized rubber and then heating it 3
`to 4 h at about I so•c.
`It is a hard substance
`and becomes soft at 700C.
`It is used for
`making covers for resistance boxes, con(cid:173)
`tainers of lead acid batteries, panel frames,
`etc.
`
`Bakelite
`It is a synthetic material of brown
`It can be moulded to make rods,
`colour.
`tubes. sheets and to any shape to suit a parti(cid:173)
`cular purpose.
`Its working temperature is
`higher ' than cbonitc and is not affected by
`It
`moisture. oil and acid.
`is a
`\·cry good
`insulating mattrial and is used for making
`electrical accessories, such as switcbe$. wall
`sockets, ceiling roses, holders, etc.
`
`Asbestos It is a white fibrous material and
`is incombustible. It is a good conductor of·
`It is manufactured into ropes. tapes.
`heat.
`sheets and sleeves.
`It is used in the form of
`sheets for
`tining
`in ovens, electric irons,
`kettles, arc shields in circuit breakers, etc.
`
`G.._ It is a tra nsparcn< insulator and Is not
`It can also be
`affected by chemical fumes.
`moulded into any shape and is brittle.
`It is
`nonhygroscopic and can withstand high 1em(cid:173)
`peratures. Jt is used in making the glass bulb
`of electric lamps, tubes, mercury arc rectifiers,
`overhead line insulators. etc. It i also used
`in making glass tapes, sleeves for a rmature
`winding, etc.
`
`Porcelain
`It is made from china clay and
`quartz sto ne and can be moulded into any
`lt is white or brown in colour and
`shape.
`is not as brittle as glass.
`It is not a ffected by
`chemical fumes and the atmosphere. Por(cid:173)
`celain is glazed to make it nonabsorptive of
`moisture. 1, is used for malcing low, medium-
`
`Mitsuba - 1011
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`and high-lension insulators of overhead lines.
`bases of swilches. k it-kat fuses, holders,
`transformer bushings, etc.
`
`It is hygroscopic, but when treated
`Paper
`with it',sul:uing oil or wax,, it becomes n good
`insulator.
`11 is cheaper than rubber aml has
`replaced rubber insulation in oil-filled power
`cables.
`It is u ed as a dielectric in condcn
`sePS and insulating ~,rands or cables.
`Leatberold or Film Leatberold
`It is a type or
`tough grey paper, chemically prepared from
`cotton rags
`in lhe form or sheets.
`It is not
`influenced by oil and grcnsc. When leathe(cid:173)
`roid is pasted with an insulating film. it is
`called a film leatheroid. They arc mainly
`used for insulating slots. bobbins. etc.
`
`Wires. Cablos and AccoS$.orres
`
`:!9
`
`Collon and Silk They serve as good insula(cid:173)
`tors when varnished. They are used on
`conductor,; required for low volta,ge instru(cid:173)
`ment wires :ind motor windings.
`
`En1me1led ln.sulatlon
`It is an insulation pre·
`pared chemically to in ulatc winding \ ire,;.
`It i cheaper than cotton nnd , ill( h ut
`is
`liable to crack with rough ilan~lling.
`
`losulatini \ arnish It is a cry good insula(cid:173)
`i-; a solution of resinous substances
`tor.
`ft
`(resin. bitumen, drying oil, etc.) in a solvent.
`On drying. the solvent evaporates, leaving the
`"base·• which hardens and becomes a varnish
`film.
`
`Dry Air Dry air is a lso a good insulator but
`wet air is not. The dry air in between the
`It is also known as
`Polyester MIiky Flla1
`conductors of overhead lines acts as an
`It is a synthetic product and
`mi/linex film.
`iosulator.
`i used in the armature rewinding of electrical
`Water
`that water is
`It should be noted
`Its sizes arc 5, 7, and 10 mils and
`machines.
`neither a good conductor nor a good insula-
`is available in kilogram rolls.
`T AIU 2.6 Cussm c1on<'N OF lNSULATOAS (As Pu, IS : 1271-19S8)
`
`SI. No.
`(/\
`
`Class
`(2)
`V (Formerly 0)
`
`Max. sefc temp.
`(J)
`
`2
`
`3
`
`6
`
`7
`
`.
`A
`
`E
`
`B
`
`F
`
`H
`
`C
`
`1os•c
`
`130°C
`
`1so•c
`
`Above
`180°C
`
`Dncrlptlon of lnsulat,ion
`(4)
`The insulation of this class consists
`or mat.crials such as cotton_._ silk,
`paper wi1hout impregnation, etc .
`Class A in~ulation consists or mAter(cid:173)
`ials such at cotton, silk, paper im•
`merscd with oil, etc.
`The insulation or this clau consists
`or materials or better quality than
`Class A materials such u leatheroid,
`paper, empire cloth, fibre, etc.
`Cius B iMUlatlon consists or mater(cid:173)
`ialssuch u mica. a)ass fibre. asbes(cid:173)
`tos. etc.
`The insulation or this class conaists
`or materials or better quality than
`insulation, such as a)ass
`Class B
`fibre, mica, asbestos. etc.
`The Insulation or this aroup consists
`or materials such as silicone eluto(cid:173)
`mer, and combinations or materials
`such as mica, glass fibre, asbestos,
`etc.
`Class C consists or materials, such
`as mica, parcelain, glass, quartz.
`CIC.
`
`
`
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`'° Basic Electrical Engineering
`
`tor. Wa ter when pure (i.e. frco from impuri(cid:173)
`ties) is a very poor conductor of electricity.
`However, when slight impuritic1 are added to
`water, it becomes a partial conductor. When
`3n acid or salt is added to water, it b«omes a
`good conductor of electricity.
`
`Gatta Percha
`It is a chemical substance and
`has properties similar to rubber.
`It becomes
`It docs not absorb mois(cid:173)
`soft at about 65°C.
`ture even if dipped in water. Therefore, it
`is used as an insulatio n for submarine cables
`and for telegraphic and telephone purposes.
`
`Sbellac It is a very good insulator.
`It is a
`natural product obtained from some varieties
`of trees in India.
`It is a mnin constituent of
`many insulating varnishes and is dissolved io
`spirit or alcohol to form shellac vnmisb.
`
`Mineral Oil Mineral oils arc excellent insula(cid:173)
`tors when free from moisture.
`It is a liquid
`insulator and is incombustible.
`It reduces
`sparking.
`It is used for filling transformer
`ta nks. cable boxes. circuit breakers, starters
`and in oil-filled paper insulated cables.
`
`Marble aad Slate They a rc also noninflamn
`able mineral insulato rs and do not absorb
`moisture. They arc going out of use nowa(cid:173)
`days due to the possibility of metallic veins in
`them.
`
`Empln Clotb Empire cloth is 11n insulating
`cloth and is used in slot linings, machines,
`It is resistant to moisture. Tape
`coils, etc.
`made from empire cloth is called empire tape
`a nd is used on the conductors of the cables
`that are subjected to work at damp places.
`
`Wood Dry wood is a n insulator. However,
`it absorbs moisture and becomes a conductor.
`Wood when treated with oil o r varnish serves
`as a good insulator for low and medium
`voltages. Therefore, it is used as wooden
`poles for overhead lines as cross-arm separa(cid:173)
`tors in lead acid batteries. for wiring boards,
`etc.
`
`2,2'7 CLASSIFICATION OP INSULATING
`MATERIALS
`Insulation may be grouped into recognized
`classes as given in Table 2.6.
`
`REVIEW QUESTIONS
`
`2.1 Name three t)'J)d o f conductors wed in overhead lines and briefty compare
`them, rcpdina their use for rmdium pressure, H .T . and E.H.T . lines.
`(NCVT 1914 W/Mo")
`
`2.2 What is the diffe re nce belWttn a wire and a cable ?
`2.3 Whal ore the conduc:tina materials wed in cables for internal house wirina?
`BrieOy explain a ny five conductors In the onier or their conductivity.
`2.4 Expl:iin any fi ve insulalina substances that are extensive ly u-SCd In the electri(cid:173)
`cal indu,cry.
`2.S What nrc the ~~n,ial propcrtin that an in.sulator must have which is used
`In chc manufacture o r a cable ?
`the differe nce between conductors and
`2.6 Give
`insulators. namina a rew com(cid:173)
`mon m:11eria1J used. Explain the use of a few d ltre~nt types of insulators that
`arc commonly used.
`2.7 (a) Why arc cabl~ stranded ?
`(b) Describe che use o f the followina cypes or wire :
`(/) Vulcani~cd insulation rubber c:a.blcs
`(II) eureka wire,
`(Ill) nich rome wire.
`(Iv) hord·drawn copJ¥:r conducto r. and
`(,·) aluminium conduc to r.
`2.R What is a st:indord wire aauge? Why is it used? Explain in brief.
`it the term used for comparins the iniulation properties of insulatlna
`2.9 Wh111
`sub tancCJ. Ghe the names o r six insulaclna mate rial• chat are used in
`Cleccrical machines. Put them in the order of a ood to bad i nsul:u ion strengths.
`(NCVT 1961 £/~c 1934 W/ffl11n >
`
`Mitsuba - 1011
`Page 7 of 7
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