ELECTRICAL MACHINES AND APPLIANCES Theory VOCATIONAL EDUCATION Higher Secondary - Second Year A Publication under Government of Tamilnadu Distribution of Free Textbook Programme (NOT FOR SALE) Untouchability is a Sin Untouchability is a Crime Untouchability is Inhuman TAMIL NADU TEXTBOOK CORPORATION College Road, Chennai - 600 006.
Government of Tamilnadu First Edition – 2011 CHAIRPERSON Dr. J. KANAKARAJ ASSOCIATE PROFESSOR DEPT. OF ELECTRICAL & ELECTRONICS ENGINEERING PSG COLLEGE OF TECHNOLOGY COIMBATORE – 641 004 AUTHORS Ms. A. Sumathi Mr.R. Krishnakumar Associate Professor Dept. of Electrical & Electronics Engg. PSG College of Technology Coimbatore – 641 004 Assistant Professor(Senior Grade) Dept. of Electrical & Electronics Engg. PSG College of Technology Coimbatore – 641 004 Mr P. Balasubramanian Mr.K.S.
HIGHER SECONDARY – VOCATIONAL COURSE ELECTRICAL MACHINES AND APPLIANCES SECOND YEAR – THEORY SYLLABUS 1. Winding Insulating Materials Introduction – Electrical properties – Classification – Characteristics – Application areas insulation materials – plastics – insulating varnishes - Types of Insulating varnishes 2. Winding Wire Introduction – Properties – Characteristics – Choice of Conductor material – Enamelled wire – Grades – Properties – Types & shapes of winding wires – Gauge plate 3.
10. Water Heaters & Coffee makers Water Heater – Function – Types – Electric Kettle – Immersion water heater – Construction and working – storage water heaters – Non pressure type – pressure type – construction and working – repairs & remedies – Coffee maker – types – construction and working of percolator type. 11.
CONTENTS Page No. 1. Winding Insulating Materials 1 2. Winding wire 15 3. Details of winding 24 4. Development of Winding - AC machines 36 5. Development of Winding - DC machines 64 6. Rewinding and Testing of Electric motors 75 7. Instruments and Testing 89 8. Electrical Cooking Appliances 97 9. Electric Iron Box 102 10. Water Heaters and Coffee Makers 109 11. Electric mixer and Egg Beaters 118 12. Vacuum cleaner and Washing machines 124 13.
1. WINDING INSULATING MATERIALS 1.1 INTRODUCTION The Electrical insulating materials are defined as materials which offer a very large resistance to flow of current, and for that reason they are used to keep the current in its proper path along the conductor. This is evident when we touch an electric machine when it is under operation. We don’t receive any electric shocks, because of the insulation.
Thus the insulating materials are grouped into different classes Y, A, B, and C with temperature limits of 900 C, 1050C and 1300C for the first three classes and no specific limit Fig.1.1 fixed for class C. Class Y and A cover the various organic materials without and with impregnation respectively, while classes B and C cover inorganic materials, respectively with and without a binder.
In the above classification Non-impregnated, moisture absorbing materials of Y- class are not generally used for motor winding insulation purposes. Since they easily absorb moisture, their quality quickly degrades. C-class materials are generally brittle, so they too are not suited for motors. Insulation materials of A and B class are being used for a long time for winding insulation purposes. In recent times F and H class are being increasingly used for winding insulation. 1.
Insulation sleeves are used to cover the joints made at the coil ends and coil leads. It gives physical protection to joints and also provides insulation. They come in rigid and flexible types. They are available for standard wire sizes. Insulation paper : A variety of insulating papers are available specifically designed for insulating electrical circuits. In motors it is used to insulate the slots, in between coils.
impregnating or trickle resins. Smooth surface, therefore good machineability, Low moisture absorption, good chemical resistance. Dielectric strength: 7 – 24 kV. Used widely as Slot insulation, slot closure, layer insulation. Triflexil is available in sheets, rolls, strips, and in thicknesses from 0.25 mm. Film paper : Polyester film is a flexible, strong and durable film with right balance of properties making it suitable for many industrial applications. It is Insulation class E (120 °C) material.
manufactured by using zinc chloride solution with paper plate. It is in grey colour or yellow colour After the coils are inserted in the slots, this is provided on the top of the slot as a protection to coils and also used as insulated between coils. Other types of boards are 1.Hard board 2.Ivory board 3.Hylum sheet Mica : It is a mineral consisting of silicate of aluminium with silicate of soda potash and magnesia. It occurs in the form of crystals, can easily be split into very thin sheets.
chokes and transformer coils etc. Silk is more expensive than cotton but takes up less space and is therefore used for windings in fractional horse power machines. Silk is less hygroscopic and has a higher dielectric strength than cotton, but like cotton it requires impregnation. The operating temperature of cotton and silk is 1000 C and the material may catch fire above this temperature. Rubber : Rubber is obtained by vulcanizing raw rubber [natural or synthetic].
resistance, and mechanical spacing of conductors in low voltage applications. Often the properties of such fabrics are upgraded by impregnation with a varnish after application. Better results are generally obtained if the fabric is impregnated prior to application. 1.8 PLASTICS : A plastic in a broadest sense is defined as any non-metallic material that can be moulded to shape.
continue to burn. This is due to its chlorine compound. This makes it an ideal construction and cable material. The incineration (burning) of PVC causes the release of toxic chemicals like dioxins and other chemicals that are harmful to humans. Thermosetting Plastics Aminos [a] Urea formaldehyde resins : They are derived from the reaction of urea with formal dehyde or its polymers. These resins cannot offer high resistance to heat.
Method of applying varnish: Applying a coating with a paint brush Vacuum pressure method Dipping the specimen into varnish Conveyorised dip method. Impregnating varnish: The main function of impregnating varnish is not electrical insulation of current-carrying conductors. but to fill the empty spaces in and around windings and to provide mechanical reinforcement of the loose grouping of conductors, even at high temperatures.
3. Sticking varnish…….Cementing cloth, paper, mica etc. 4. Core-plate varnish[air drying, baking and flashing]………..Insulating armature and transformer laminations. The air drying is not suitable for oil-immersed operation. 5. Epoxy resin varnish [baking]……..All coil impregnation, internal curing, where superior durability and chemical and moisture resistance are required. 6. Silicone resin varnish [air drying and baking]………..
12 Bakalized fabric strip or Epoxy fibre glass strip or Bamboo strip Bakelized fabric strip or Epoxy fibre glass strip or Bamboo strip Alkyd varnished terylene or glass tape or sleeving Alkyd phenolic Slot closure (wedge) Insulation for leads Varnish for impregnation treatment Alkyd phenolic No extra insulation because the phase-tophase insulation itself is sufficient Nomex sheet Mica alkyd bonded to glass cloth Melinex film bonded to press board Phase (or coil) to earth insulation Estermide or
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1) Insulating materials are used between A) Conducting materials and Non-conducting materials B) Two non-conducting materials C) Two conducting materials (both not part of current carrying circuit) D) Two conducting materials (of which only one is part of current carrying circuit) 2) Identify which one of the following is Liquid Insulating material A) Rubber B) varnish C) Argon D) paper 3) Thermal Insulation class to which MICA belongs is B) Clas
Part - B Answer the following questions in one or two words (1 Mark) 1. What property should be more for the insulating material to be thinner? 2. Which classes of insulating material can withstand temp.s of 155o C and 180o C respectively? 3. What is the insulation class of NOMEX material? 4. In motor winding applications, where film paper is used? 5. What is the name of the MICA splitting bonded to electrical grade paper? 6. Which is called as secondary insulation in a motor? 7.
2. WINDING WIRE 2.1 INTRODUCTION Winding wire is solid wire, which, to allow closer winding when making electromagnetic coils, is insulated only with varnish, rather than the thicker plastic or other insulation commonly used on electrical wire. It is used for the winding of electric motors, transformers, inductors, generators, speaker coils, etc. A wire is a single, usually cylindrical or rectangular cross-section, length of metal. Wires are used to carry electricity and telecommunications signals.
sensitive to impurities. 2) It is reddish-brown in colour. 3) It is malleable and ductile. 4) It can be welded at red heat. 5) It is highly resistant to corrosion. 6) Melting point is 10840C 7) Specific gravity of copper is 8.9. 8) Electrical resistivity is 1.682 micro ohm cm. 9) Its tensile strength varies from 3 to 4.7 tonnes/cm2. 10) It forms important alloys like bronze and gun-metal. Copper is very widely used in wires, cables, windings of generators and transformers, overhead conductors, busbars.
2.4 ENAMELLED WIRE: Enamelled wire is a wire coated with a very thin insulating layer. The core material (‘wire’) is copper or aluminum, coated with a thin layer of a polyurethane, polyamide, or polyester resin - called as “enamel”. The thin layer of insulation coated on Enamelled wire, prevents the wire surfaces from being in a short circuit when wound into coils. It is used mainly in the construction of motors, electromagnets, transformers and inductors.
13 0.092 2.337 4.29 39 0.005 0.132 0.0137 14 0.080 2.032 3.24 40 0.005 0.122 0.0117 15 0.072 1.829 2.63 41 0.004 0.112 0.0098 16 0.064 1.626 2.07 42 0.004 0.102 0.0082 17 0.056 1.422 1.59 43 0.004 0.091 0.0065 18 0.048 1.219 1.17 44 0.003 0.081 0.0636 19 0.040 1.016 0.811 45 0.003 0.071 0.0557 20 0.036 0.914 0.657 46 0.002 0.061 0.0479 21 0.032 0.813 0.519 47 0.002 0.051 0.0400 22 0.028 0.711 0.397 48 0.002 0.041 0.0322 23 0.
Table 2.2 showing increase in dimensions due to enamel (synthetic) covering Grade of covering Fine Medium Thick Minimum increase (mm) 0.035 0.060 0.100 Maximum increase (mm) 0.060 0.100 0.150 2.6 PROPERTIES OF ENAMELLED WIRES : Excellent dielectric strength. Very low dissipation factor, remaining reasonably constant at high frequencies or under humid conditions. No mechanical or chemical stripping required. Adequate ventilation required when tinning or soldering.
Table 2.3 A sample of gauge No.s and its equivalent are given in the following table. Standard Gauge Number 2. 3. 4. 5.
The circular forms of wire gauge measurement devices are the most popular, and are generally 3 3/4 inch. (95 mm) in diameter, with thirty-six notches; may have the decimal equivalents of the sizes stamped on the back. Oblong plates are similarly notched. Many gauges are made with a wedge-like slot into which the wire is thrust; one edge being graduated, the point at which the movement of the wire is arrested gives its size. The graduations are those of standard wire, or in thousandths of an inch.
QUESTIONS Part - A Choose the Correct Answer 1. (1 Mark) To transfer power without much loss of power, the conductor material should be A) Very light C) have very low resistance 2. B) very strong D) have very low weight. Copper is very widely used in electrical wires because, (i) It has high conductivity, (ii) it has high tensile strength, (iii) It is very flexible, (iv) it is good conductor of heat. A) (i) (iii) & (iv) 3. 4.
7. Enamelled wires should not be used beyond this temperature. What it is? 8. If during rewinding same gauge winding wire is not available then we can use several runs of lesser gauge wire in place of previous one. Which parameter should be same in both the cases? 9. What is the equivalent size in mm for 1 mil? 10. What is the name of the plate which is used to find the size of wires? Part - C Answer the following question briefly (4 Marks) 1. What is meant by conductor? 2.
3. DETAILS OF WINDING 3.1 DETAILS ABOUT THE WINDING COIL A length of wire lying in the magnetic field and in which an emf is induced is called a coil. The coils used in windings are shown in Fig. 3.1. Back end side B C Active sides N S A D N S Front end side S F b) Multi turn coil a) Single turn coil Fig.3.1 - Winding Coil representation Fig. 3.1 (a) represents a coil with only one turn in it. Each coil has active and inactive sides. A coil can in general have any number of turns.
starting end S and finishing end F of a coil. In Fig. 3.1 (a), AD and BC represents the inactive sides of a coil. Coil Groups : One or more coils connected in series are called coil groups, as shown in Fig. 3.2. The number of coil groups is equal to the number of poles. In Fig. 3.2, there are four coil groups, which are equal to four numbers of poles. For AC winding, the total number of coil groups depends upon the number of poles and the number of phases. ∴ the total number of Coil groups = mP 3.
á = xâ for short pitch winding 3.7 Also â = 180 S/p where á = short pitch angle or an angle less than 1800ε 3.8 â = angle between adjacent slots x = 1, 2, 3, . . . an integer Example 3.3 : Find the angle between adjacent slots of a 3 phase, 6 pole motor having 36 slots. Solution : Slots per pole = 36 180 = 6 From equation 3.8, â = = 30oε 6 S/p Pitch Factor or coil span factor or chording factor, KP: When the two sides of the same coil are short pitched by an angle á, as shown in Fig. 3.
Solution :From equation 3.11, m = 180 â= s 36 = 3 From equation 3.8, angle between adjacent slots, 3x4 180 = 36 = 200. From equation 3.10, Kd = = 0.96 p 4 Winding Factor, KW : It is defined as the product of pitch factor and distribution factor. KW = KPKd 3.12 Example 3.6 : Find the winding factor for the Example 3.5. Solution : From equation 3.9, KP = From equation 3.12, KW = KPKd = 0.96 x 0.94 = 0.
Thus, mechanical degree in terms of poles where 3.13 θmd = mechanical degree. Mechanical degree in terms of slots where 3.14 â m = mechanical degree between adjacent slots, S = number of slots Consider a 4 pole machine, as shown in Fig. 3.4 (c). Point A is under North pole N1 and marked as 00ε. Moving clockwise, point B is situated at 900md from point A. But point B is under South pole S1, which is magnetically opposite to N1. Hence, point B is marked as 1800ε.
Fig.3.5 - Double layer windings Fig.3.6 - Single layer winding 3.2 DIFFERENT SHAPE OF SLOTS : There are different shapes of slots used for electrical machines. The slots used in the stator of induction motors, may be completely open or semiclosed as shown in Fig. 3.7 (a). (a) Semi-closed and open slots (b) Types of rotor slots (c) Semi-closed and open slots used in dc armatures Fig.3.
3.3 SLOT INSULATION : Materials used for slot insulation are leatheroid, mica, glass cloth, and flexible type of micanite. The type of slot insulation will vary according to the capacity of the machine. Slot Liner : The slot liner is an insulation sheet cut to the inner dimensions of the slots and projected on either side of the slots. In some applications, the edges of the slot liner are folded on either end to prevent them from sliding in the slots, as shown in Fig. 3.8. Fig.3.
Back Pitch, Yb : It is the distance between the two active sides of the same coil under adjacent opposite poles. For double layer winding, 3.17 where K = any integer or fraction, added or subtracted with , that will give the value of Yb an odd integer. Front Pitch, Yf : It is the distance between two coil sides connected to the same commutator segment. It should be an odd integer.
From equation 3.18 the winding pitch, Y =+ 2 = 2 (even integer) From Fig. 3.9 or from equation 3.20, front pitch, Yf = 11 –2 = 9 or 13 – 2 = 11 (odd integer). 3.9 WAVE WINDING: When the finishing end of the first coil is connected to the starting end of the next coil, as shown in Fig. 3.10, which starts from the next adjacent pole where the first coil started is known as wave winding. From Fig. 3.10, for wave winding, the front pitch, Yf = Y - Yb 3.21 Example 3.
half the number of poles in the machines, as shown in Fig. 3.11 (b). In this type, however, each coil may have twice the number of turns of a whole coil winding or two coils under a north or south pole of the latter type may be connected in series and taped together to form one coil. The main difference between full coil and half coil windings is in the method of making the end connections for the coils. 3.
3.18 CONCENTRIC WINDING : Concentric windings are single layer windings. This winding has two or more than two coils in a group and the coils in each group have the same centre. In each group, the coil pitch is not equal and therefore do not overlap each other, as shown in Fig. 3.12. The coil span of the individual coils is different. The coil span is more than a pole pitch while the span of others is equal to or less than the pole pitch.
6. The electrical degree between adjacent slots for a 4 pole machine having 36 stator slots is A) 100 B) 100ε C) 200 D) 200ε 7. The short pitch angle, á, of a 4 pole 3 phase winding ac machine wound with a coil span of 1400ε is A) 400ε B) 1800ε C) 900ε D) 600ε 8. In three phase winding, three single phase windings are _____________ apart. B) 1200ε C) 900ε D) 600ε A) 1800ε 9.
4. DEVELOPMENT OF WINDING - AC MACHINE 4.1 AC SINGLE PHASE WINDINGS AC Lap Winding : Develop a single phase, single layer AC lap winding for a 4 pole AC machine having 24 slots. Solution : In single layer winding, the number of coil is equal to half the number of slots on the stator, so that each slots contains only one coil side. Therefore, number of coils, C = 12 Number of slots From equation 3.
To draw the main winding diagram, solid lines of equal length and equal distance equal to number of slots is drawn. Connect the coils as per the Winding Table 4.1. Arbitrarily assume a particular current direction to the coil sides under the pole pairs. For the coil sides under North Pole regions, assume downward current direction and vice versa for the South Pole regions, as shown in Fig. 4.1. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 N1 S1 S2 N2 Fig.4.
Table 4.2 Single Phase AC Wave Winding Table S.No. Yf Yb 1 2 3 4 5 6 7 8 9 10 11 1 13 2 14 3 15 4 16 5 17 6 7 19 8 20 9 21 10 22 11 23 12 12 18 24 To draw the main winding diagram, solid lines of equal length and equal distance equal to number of slots is drawn. Connect the coils as per the Winding Table 4.2. Arbitrarily assume a particular current direction to the coil sides under the pole pairs.
coil side 9, ie., pitch for larger coil is added to coil side 4. The front end of the coil side 9 is connected to front side of coil side 5 to form concentric winding. Following the above procedure, Table 4.3 gives the complete winding table for 4 pole 24 slot AC Machine. Table 4.3 Single Phase Concentric Winding Table S.
From equation 3.5, slots per pole = 12 = 6 2 180 180 From equation 3.8, angle between consecutive slots, â = slots per pole = 6 = 300. The allotment of slots to the three phases for a pole pair is given in Fig. 4.4, and this allotment repeats itself for other pole pairs. In this example, the number of pole pairs is one. Pole pitch 1 2 R 3 4 B Pole pitch 5 6 7 Y 8 R 9 10 11 B 12 Y Fig.4.
Fig. 4.6 gives the complete main winding diagram for a 2 pole 12 slots ac machine using single layer half coil winding. In Fig. 4.6, RS, RF, BS, BF, YS, and YF indicate the starting and finishing ends of RBY phases respectively. Fig.4.6 - 3 phase 2 pole single layer winding main winding main winding diagram (Half coil) Whole Coil Winding The whole coil winding has one coil group per pole for each phase.
To draw the main winding diagram, draw 12 solid lines of equal length and distance equal to the number of slots, as shown in Fig. 4.8. For series connection, the finish of first coil of a phase is connected to the finish of the second coil group of the same phase. The start of the second coil group is connected to the start of the third coil group and so on. In Fig. 4.8, RS, RF, BS, BF, YS, and YF indicate the starting and finishing ends of RBY phases respectively. Fig.4.
in such a manner that their emfs add. The windings of the other phases are also similarly completed. The current directions marked in Fig. 4.9, is an arbitrary direction at any instant. Problem 2 : Develop a 3 phase, single layer concentric type of winding for a 4 pole ac machine having 24 slots. 24 24 Solution : Slots per pole per phase = 3x4 = 2 , From equation 3.5, slots per pole = =6 4 180 180 From equation 3.8, angle between consecutive slots, â = = = 300.
44 Fig. 4.
Fig. 4.11 gives the coil group connections for half coil winding for each phases. They form a coil group. The rule for connecting together the coils in a coils group is that the end wire of one coil must be connected to the beginning of next coil in the group and so on. This is done in order that the emfs of the coils in a coil group, add. Fig. 4.12 gives the complete main winding diagram for a 4 pole 24 slots ac machine using single layer half coil winding. In Fig. 4.
Fig. 4.14 - 3 phase 4 pole 24 slots single layer winding diagram (whole coil) Mush winding In drawing this winding, the slots are numbered from 1 to 24 and the long and short sides are alternatively drawn, as shown in Fig. 4.15 If the first phase, say R or A phase starts at slot no.2, the Y or B phase should start at 1200/ 300 = 4 slots away ie., slot (2 + 4 = ) 6, and the B or C phase should start at (6 + 4 =) 10. Slots per pole per phase = 24 3x4 = 2. Thus a phase group has 2 slots.
47 Fig. 4.
Pole pitch 1 2 3 R 4 5 6 7 8 9 B 10 11 12 Y Fig. 4.16 - Slots per pole per phase Half coil winding If the first phase, say R or A phase starts at slot no.1, the Y or B phase should start at 1200/150 = 8 slots away ie., in slot (1 + 8 = ) 9, and the B or C phase should start at (9 + 8 =) 17. The winding should be connected between alternate North and South poles. First, R or A phase winding is started. If one side of the coil is placed in slot no.
Fig. 4.18 - 3 phase 2 pole 24 slots single layer winding main winding diagram (half coil) Whole Coil Winding 12 24 Total number of coils = = 6; Coils per phase = = 4; Number of coils of groups per 3 4 phase = 3 x 2 = 6 If the first phase, say R or A phase starts at slot no.1, the Y or B phase should start at 1200/150 = 8 slots away ie., in slot (1 + 8 = ) 9, and the B or C phase should start at (9 + 8 =) 17. Starting with coil in slot no. 4, the start of R phase lies in slot no.
Fig. 4.19 - Coil group connections for whole coil winding Mush winding In drawing this winding, the slots are numbered from 1 to 24 and the long and short sides are alternatively drawn, as shown in Fig. 4.21. If the first phase, say R or A phase starts at slot no.2, the Y or B phase should start at 1200/150 = 8 slots away ie., in slot (2 + 8 = ) 10, and the B or C phase should start at (10 + 8 =) 18. Slots per pole per phase = 24 3x2 = 4. Thus a phase group has 4 slots. 24 Coil span = 2 = 12 slots.
51 Fig. 4.
52 Fig. 4.
Double layer windings Lap winding Problem 1 : Develop the layout of a lap winding for a 3 phase ac machine having 4 pole and 24 slots. There are 2 coil sides per slot. Solution : Coil groups per phase = 3 x 4 = 12 Slots per pole per phase, m = 24 3x4 =2 180 Angle between adjacent slots, â = 24 = 300ε. 4 For full pitch coils, the coil span, á = 0, ie., angle between the two sides of the same coil is 1800e. 180 180 1800 corresponds to = = 6 slots.
Table 4.5 gives the winding table for RYB Phases. Table 4.5 Winding Table for RYB Phases S.No. Top coil side (-Yf) Bottom coil side (+Yb) R or A phase per pole per phase 1 1 14 2 3 16 3 13 26 4 15 28 5 25 38 6 27 40 7 37 2 8 39 4 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 Y or B phase per pole per phase 9 22 11 24 21 34 23 36 33 46 35 48 45 10 47 12 B or C phase per pole per phase 5 18 7 20 17 30 19 32 29 42 31 44 41 6 43 8 Fig. 4.
55 Fig. 4.
180 180 = = 12 slots. 1800 corresponds to 15 â There are 3 phase groups per pole, each comprising of 4 slots. The distribution of slots, of phase sequence RYB or ABC, is shown in Table 4.6. Table 4.6 Polar Groups Poles North South R 1–4 13 - 16 B 5–8 17 – 20 Y 9 – 12 20 - 24 Phase The start of the phases must be displaced by 1200 and so must be finishes. If the start of R or A phase lies in slot no. 1, the start of Y or B phase must be in slot no. (1 + that of B or C phase in slot no.
57 Fig. 4.
Short Pitch Winding It is assumed that the winding is short pitched by 1 slot. Therefore, coil span = 11, in terms of slots, or Yb = 23 in terms of coil sides. The winding pitch, Y = +2 (progressive winding). The front pitch, Yf = Yb – Y = 23 – 2 = 21 in terms of coil sides. Table 4.8 gives the winding table for RYB or ABC Phase, in terms of coil sides. Table 4.8 Winding Table for RYB Phases in terms of coil sides S.No.
Fig. 4.24 - 3 phase double layer 2 pole 24 slot lap (short pitch) winding Fig. 4.24 gives the main winding diagram for the 3 phase, 2 pole, 24 slot machine ac machine.
Wave winding Problem 3 : Develop the layout of a wave winding for a 3 phase having 4 pole ac machine and 24 slots. There are 2 coil sides per slot. 24 s Solution : Coil groups per phase = 3 x 4 = 12 . Pole pitch = p = 4 =6 180 24 Slots per pole per phase, m = = 2. Angle between adjacent slots, â = 24 = 300. 4 3x4 There are 3 phase groups per pole, each comprising of 2 slots. The distribution of slots, of phase sequence RYB or ABC, is shown in Table 4.9. Table 4.
61 Fig. 4.25 - 3 phase double layer 4 pole 24 slot wave Fig. 4.25 gives the complete main winding diagram for 3 phase 4 pole 24 slot double layer wave winding.
QUESTIONS Part - A Choose the Correct Answer 1. (1 Mark) In single layer winding, the number of coil is equal to ____________, so that each slots contains only one coil side. A) the number of slots on the stator C) synchronous speed 2. B) the number of poles D) half the number of slots on the stator Pole pitch is defined as A) number of slots per pole C) coil sides per slot 3.
Part - C Answer the following questions briefly (4 Marks) 1. Calculate the front, back and winding pitches for a single phase, single layer AC lap winding for a 4 pole AC machine having 24 slots. 2. Calculate the front, back and winding pitches for a single phase, single layer wave winding for a 4 pole, 24 slot ac machine. 3. Calculate the angle between the adjacent slots for a 3 phase, single layer concentric type of winding for a 2 pole ac machine having 12 slots. 4.
5. DEVELOPMENT OF WINDING - DC MACHINE 5.1 GENERAL PROCEDURE FOR DEVELOPMENT OF WINDING DIAGRAM 1. Calculate the number of coil sides for the main winding diagram. 2. Calculate the back pitch, Yb, the winding pitch, Y, and the front pitch, Yf, using equations 3.17, 3.18, and 3.20 respectively. 3. Form a winding table using the back pitch, Yb, and the front pitch, Yf. 4. For drawing the main winding diagram, draw solid vertical lines of equal length at equal distance equal to number of coils.
From equation 3.3, the winding Pitch, Y = +2 for progressive winding (even integer). From equation 3.5, the front pitch, Yf = Yb – Y = 7 – 2 = 5 (odd integer). Starting with coil side 1 (back end side), back pitch is added to obtain the bottom layer coil side, ie., 8 (back end side). To the coil side 8 (front end side), front pitch is subtracted to obtain the top layer coil side, ie., 3 (front end connection).
Find the current direction by applying Fleming’s right hand rule, when the mode of operation is a generator and Fleming’s left hand rule, when the mode of operation is a motor. Or the current direction to all coil sides can be arbitrarily assumed. Mark downward current direction for the coil sides under the north pole regions and upward current direction under south pole regions, as shown in Fig. 5.1.
From Fig. 5.3, it can be seen that the number of parallel paths in a lap winding, will be equal to number of poles. where A=P 5.1 A = number of parallel paths; P = number of poles The current through each armature coil / conductor will be the ratio of the total armature current by the number of parallel paths, ie., I 5.2 I= A A where I = current through each armature conductor/coil; IA = total armature current 5.
19 21 23 3 1 5 7 9 N 23 11 13 15 S 17 19 21 4 6 8 10 12 1 2 3 4 5 - - + 2 14 16 18 20 22 24 6 7 8 9 10 11 12 + - - + + AA 4 6 S N 2 23 2 A Fig. 5.4 - Main winding diagram To fix the brush arm positions, commutator ring diagram is used, as shown in Fig. 5.5. 1 5 8 9 12 3 7 10 14 + 17 13 20 16 + - 11 15 - 4 24 + 19 22 18 1 21 - 3 23 2 + 6 - Fig. 5.5 - Commutator ring diagram Now, transfer the brush arms to the main winding diagram.
Starting with top layer of coil side 1 (back end side), back pitch is added to obtain the bottom layer coil side, ie., 6 (back end side). To the coil side 11 (front end side), front pitch is added to obtain the top layer coil side, ie., 4 (16-12) (front end connection). Proceeding in similar way, all the coil sides are connected and Table 5.3 gives the winding table for 2 pole 6 slot simplex wave winding. Table 5.3 : Winding table for 2 pole, 6 slot simplex wave winding S.No.
To fix the brush arm positions and to find the number of parallel paths offered by the armature winding, commutator ring diagram is used, as shown in Fig. 5.7. Draw the vertical solid lines equal to number of coil sides and join them with reference to Table 5.3, as shown in Fig.5.7. Also mark the current direction through the coil sides with reference to main winding diagram in Fig. 5.7. Look for adjacent pair of coil sides having the same current direction.
IA A I = current through each armature conductor/coil; IA = total armature current I= where Problem 2 : Develop a winding diagram for a 4 pole, 13 slot double layer simplex wave connected dc machine with 13 commutator segments. Indicate the position of brushes. Solution: Number of coils, C = number of commutator segments = 13; Number of coil sides = 2C = 26; Therefore, coil sides per slot = 6.5 + 0.
72 20 1 22 24 21 23 25 2 26 1 + 3 2 3 4 5 A 6 7 6 8 9 - 7 10 S1 11 8 12 13 9 14 + 11 12 - 13 22 24 20 25 16 18 21 23 S2 19 N2 17 10 AA 15 Fig. 5.
for the coil sides under the north pole regions and upward current direction under south pole regions, as shown in Fig. 5.9. To fix the brush arm positions and to find the number of parallel paths offered by the armature winding, commutator ring diagram is used, as shown in Fig. 5.10. Look for adjacent pair of coil sides having the same current direction.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. The value of back pitch of a dc armature winding should be A) a even integer B) an odd integer C) equal to one D) a prime number 2. When a dc machine is operating as a generator, to find the current direction in the armature winding ________________ is used. A) Fleming’s left hand rule B) Ohm’s law C) Fleming’s right hand rule D) Kirchhoff’s law 3.
6. REWINDING AND TESTING OF ELECTRIC MOTORS 6.1 METHOD OF REWINDING To start the armature winding, the armature is mounted on the winding stand as in Fig. 6.1, then the shaft, armature core and slots are insulated as per the insulation scheme taken from the data. Fig. 6.1 - Armature on winding stand 6.
A loop is made at the end of the first coil and the beginning of the second coil. The second coil is started in the designated slot and the coil is wound with the same number of turns as in coil 1. The span of coil 2, has to be equal to that of coil 1. When the second coil is finished, a loop is made again and then the third coil is started. In this manner the winding is continued, until all the coils have been wound. The end lead of the last coil is connected to the beginning lead of the first coil.
Lead swing : One of the most important operations in winding an armature is to lace the coil leads in the proper commutator bars. Leads may be placed in the bars in any of the three different positions, depending on the original location. Fig. 6.5 Fig. 6.6 The following method is used in determining the position of the leads in the commutator. Stretch a piece of cord or string through the centre of a slot, as shown in Fig. 6.7, a, b,& c.
Soldering: For soldering, electric irons are generally used on small armatures and gas irons on the larger ones. The size of the iron used depends on the size of the commutator. Leads are soldered to the commutator by means of soldering iron or torch. The procedure of soldering is as follows. First the soldering flux is applied over the wires to be soldered and also the identified commutator raiser. The wires are then laced in the respective raisers.
Brazing: In the case of large armature windings, the armature winding lead ends are brazed with the respective commutator raiser slits by means of a gas torch. Close inspection and care should be exercised in the control of the flame. Hot stacking : In the case of small DC armature conductors are kept in the commutator raiser slits and spot welded. This is called hot stacking. A specially designed hot-stacking machine is available for this purpose.
After winding several turns over the loop, insert the last end of the cord band through the loop, and then pull the free end of the loop. This will pull the end under the Core band and secure it there. Then the pulled end of the cord can be cut off. Use enough pressure in winding so that the band will be tight. Steel bands : Steel bands are laced on the front and back ends of the coils. These bands are up on the armature in a different manner than in the cord bands. The procedure is illustrated in Fig. 6.
Baking and varnishing : After the armature has been wound, soldered and banded and tested, the next operation is varnishing. This process makes it moisture-roof and also prevents vibration of the coils of wire in the slots. Vibration has a tendency to impair the insulation on the wires and cause shorts. Moisture will also cause the insulation on the wires to deteriorate. Before varnishing the armature, it must be reheated to drive cut the moisture on it.
Dynamic balancing : Dynamic balancing machines are available to balance the armature or rotating the arts of electrical machines. The armatures are fixed on those machines and rotated at the rated seed. A pointer or an indicator shows the position on the armature and the weight to be added. The balancing machines available are either with the mechanical balancing or with the stroboscopic balancing. 6.
6.4 INSULATION RESISTANCE TEST : With a bar copper wire, short all the commutator segments, as shown in Fig. 6.14. Test the insulation resistance between the body and the commutator or segments by a 500V Megger, for armatures rated upto 250 volts. The IR so measured shall be greater than 1 mega-ohm. If the value is less than 1 megaohm, moisture in the winding or a weak insulation is to be suspected. This test is sometimes conducted by a series test lam and is called the ground test.
An external growler shown in Fig. 6.15 is an electromagnetic device that is used to detect and locate grounded, shorted and open coils in an armature. This growler consists of a coil wound around an iron core and is connected to a 240 volt AC line. The core is generally H shaped and cut out on to so that the armature will fit on it, as shown in Fig. 6.16. Fig. 6.16 When an alternating current is applied to the growler coil, the voltage will be induced in the armature coils by transformer action.
Growler test for grounded coil : The armature to be tested is placed on the growler and then the growler is switched ‘ON’. Place one lead of an AC milli-voltmeter on the to commutator bar the other meter lead on the shaft, as shown in Fig. 6.18. Fig. 6.18 If a reading is noticed on the meter, turn the armature so that the armature so that the next commutator bar is in same position as the earlier one, and test as before. Continue in this manner until all the bars are tested.
In case of short in the winding, the blade will vibrate rapidly and create a growling noise. If the blade remains stationary, it is an induction that no short exists in the coil under test. After several to slots have been given the hacksaw blade test, turn the armature so that the few slots are on to. Test as before and continue this procedure for the entire armature. An armature having cross connections or equalizers cannot be given the hacksaw blade test.
Adjust the readings to a specified value, by using a variable rheostat. Record the millivoltmeter readings on the consequent commutator segments by rotating by rotating the armature Fig. 6.21 in one direction. The position of the segments and the connection should be the same as in the first set up. The result could be concluded as enumerated below. 1) 2) 3) 4) If all the readings are the same, the winding is correct. If the millimeter reads zero or low voltage, the coil connected to the segment is short.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. In double layer winding to ensure that all the coils have the same pitch and turns, there will be ____________ coil side(s) in each slot A) one B) four C) six D) two 2. One of the most important operations in winding an armature is to lace the coil leads in the proper A) commutator bar B) armature slot C) brushes D) poles 3. The size of the iron used for soldering depends on the size of the A) brushes B) poles C) stator D) commutator 4.
7. INSTRUMENTS AND TESTING 7.1 INTRODUCTION In this modern world, use of electricity everywhere is inevitable. As almost all industrial machines, home appliances etc. are working on electrical energy, it is must to inspect and test the electrical energy for its quality before energizing machines/appliances. Also if the machines/ appliances are not working on giving electrical energy, it is required to carry out some test to identify the fault. So here we will see few basic testing instruments and their use.
Multimeter/Continuity test Continuity testers are simple devices designed to verify a complete electrical path through an object or circuit. They are especially useful for checking fuses of all types, light-bulbs, and wire paths. This tester is usually comprised of: 1. Two leads 2. A small body where the leads meet and contain... 3. Some form of indicator A number of devices are manufactured to assist consumers in testing electrical continuity, ranging from multimeters as shown in Fig.7.
like the water pipes in your kitchen or bathroom. This can cause electrical shock in the shower or sink. Leaking current also results in higher electric bills. In addition, it can cause the ground faults in your home to trip repeatedly and eventually overheat. Fig.7.3 - Open circuit test Fig.7.
aluminum ‘C’ former of peculiar shape. The pressure coil is connected across the sourced through resistor of 0.1 MW as shown in Fig. 7.6. Fig. 7.
Precaution while using Insulation tester (megger): 1. Portable testers (meggers) come in 50, 100, 250, 500 or 1000 volts. It is important to use the right tester for the right system. Low voltage testers are required for low voltage systems, and high voltage testers for high voltage. Higher voltage is generally used for commercial systems, motors or transformers. Some digital testers work over a range of voltage and can be set for higher or lower volts. 2.
3-phase AC circuit: i) One wattmeter method : Fig.7.12 - Single wattmether method of power measurement in 3-phase circuit For balanced 3-phase load i.e. ZR = ZY = ZB, single wattmeter may be connected into any one phase as shown in fig. 7.12. This wattmeter will indicate the power in that phase only.
QUESTIONS Part - A Choose the Correct Answer 1. (1 Mark) By performing continuity test, we can determine i. ii. existence of any open circuit in the electrical network existence of any short circuit in the electrical network Choose the correct choice among the following. A) i alone is correct 2. B) ii alone is correct D) both are wrong While touching the two probes of multimeter together, the meter should read A) zero ohm B) infinite ohm D) produce beep sound 3.
4. When is the 3-phase load said to be balanced? 5. Two wattmeter method of power measurement can be used for 3-phase, 3-wire system for both balanced and unbalanced loads. Say TRUE or FALSE. Part - C Answer the following questions briefly (4 Marks) 1. Explain briefly the construction and application voltage tester. 2. Explain briefly the application of multimeter to perform open circuit and short circuit test. 3.
8. ELECTRICAL COOKING APPLIANCES 8.1 INTRODUCTION An electric stove converts electricity into heat to cook and bake. The first technology used resistive heating coils which heated iron hotplates, on top of which the pots were placed. In the 1970s, glass-ceramic cooktops started to appear. Glassceramic has very low thermal conductivity, but lets infrared radiation pass very well. Electrical heating coils or infrared halogen lamps are used as heating elements.
Fig. 8.3 - Connecting leads Grill Stand : It is made of chromium/nickel plated MS rods and hinged to the body. It supports the vessels kept on the heater and acts as a barrier between the exposed heater element and the vessel, as shown in Fig. 8.4. For safety, this grill should have electrically continuity to the body, and both must have earth connection. A properly earthed grill and body will enable the fuse to blow in case of accidental contact of live parts with them, thereby avoiding shock to the user.
Fig. 8.6 - Bread toaster In Fig. 8.6, 1. Electrical energy flows into the toaster from a wire plugged into the domestic electricity supply. 2. The electric current flows through a series of thin filaments connected together but spaced widely enough apart to toast the whole bread surface. 3. The filaments are so thin that they glow red hot when the electricity flows through them. 4. Like a series of small radiators, the filaments beam heat toward the bread in the toaster. 5.
Operation : It consists of three working parts 1. A bread carriage moves up and down inside the toast well and it has usually an external control knob. The carriage operates a switch that turns the toaster on and off. 2. Heating elements, made of resistance wires, are positioned on both sides of each toast ‘well’. When current flows through them, they radiate heat for toasting. 3. A thermostat inside the toaster is linked to a toast color control outside.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. An / A _______________ converts electricity into heat to cook and bake. A) electric toaster B) electric stove C) fridge D) grinder 2. The heating element used in electric stove is made of ________ wire. A) Nichrome B) Copper C) Aluminum D) Lead 3. ________________ withstands high temperature and remains as a good insulator even at high temperatures. A) Copper B) Aluminum C) Nichrome D) Porcelain 4.
9. ELECTRIC IRON BOX 9.1 DEFINITION An Electric Iron box is a heating device in which the electrical energy is converted into heat energy. This heat energy is concentrated on a smooth, flat bottom surface which is pressed over the cloth to be ironed. 9.2 TYPES OF IRON BOX: 1) Non-automatic Iron box 2) Automatic Iron box 3) Steam Iron box 9.3 NON-AUTOMATIC IRON BOX : In non-automatic type, the temperature is not regulated. The user has to switch ON or OFF the iron as per the heat requirement.
Fig.9.2 - Heating element (type 1) Fig.9.3 - Heating element (type 2) Fig. 9.4 - Terminal and power cord Working of iron box: When electric supply is given to the heating element using 3-core power cord, the heat produced in the element will be transferred to the sole-plate which is then pressed over the cloth to be ironed. Thus the iron converts the electricity into heat at the sole-plate. The heat at the sole-plate is used to iron the clothes.
rates welded together. The metal strip expands when heated and contacts when cooled. One metal in the bimetal strip has a high rate of expansion when heated and the other has a low rate. When a bimetal strip is heated both the metals in the strip expand but the one at the bottom as shown in Fig.9.7, with a high rate of expansion, expands faster and forces the upper half to curl up or bend away from the contact point. The strip curls or bends enough to break the contact, i.e. opening the circuit.
Pilot lamp : It is used to indicate the flow of current. The lamp condition and its indication are given in table II. Indication Lamp condition Glowing Not glowing The temperature is within predetermined value and the current is flowing The temperature is more than the predetermined value and the current is not flowing. 9.5 DIFFERENCES BETWEEN NON-AUTOMATIC AND AUTOMATIC IRON BOX: Sl. No Non-automatic type Automatic type 1 It does not consist of thermostat switch.
Fig.9.9 - Outline of steam iron box When the element is found to be defective, sole plate along with the sealed heating element has to be replaced. Distilled water is recommended for filling into the tank. Ordinary water, if used, may result in deposition of salts in the tank and clog the entry and exit ports. It is recommended to flush the water in the tank by pressing the steam control knob fully for some time before the iron is switched off keeping it till next use.
Trouble Possible causes Corrective action to be taken Excessive heat First repair the thermostat control. Then replace or repair the sole-plate, depending on its condition. Tears clothes. Rough spot, nick, scratch, burn on sole-plate. Remove these spots with fine emery and polish the area with buff. Iron cannot be turned off Thermostat switch contacts are welded together. Check the thermostat switch contact. Open them by force.
4. The purpose of thermostat in Automatic iron box is to A) increase temperature B) decrease temperature C) regulate temperature D) monitor temperature 5. In bimetallic thermostat, i) one metal plate has a high rate of expansion when heated and the other has low rate ii) both metal has same rate of expansion when heated A) i alone is correct B) ii alone is correct C) both are correct D) both are wrong Part - B Answer the following questions in one or two words (1 Mark) 1.
10. WATER HEATERS AND COFFEE MAKERS 10.1 FUNCTION OF WATER HEATERS It is used to heat small or bulk quantity of water. The heating element of water heaters converts electric energy into heat by which water inside the heater gets heated due to convection. 10.2 TYPES OF WATER HEATERS The water heaters are available in various forms. They are i) Electric Kettle ii) Immersion water heater iii) Storage water heater (Geyser) 10.3 ELECTRIC KETTLE It is used to heat small quantity of water.
1. Bolt, nut and washer holding bottom cover 2. Heating element 3. Asbestos sheet 4. Sole-plate 5. Pressure plate 6. Bottom cover 7. Handle 8. Top lid 9. Ebonite leg 10.Outlet socket 11. Brass strips Fig.10.3 - Saucepan type Electric kettle Asbestos sheet : This is placed below the heating element and mica insulation to serve as a heat insulator. Also It reduces the heat loss in the kettle. Sole plate : The sole plate is made of cast iron and is of flat surface.
10.5 IMMERSION WATER HEATERS: An immersion water heater is a very simple appliance which heats a bucket of water in a 10 to 15 minutes. It consist of a heating coil has a chord similar to an electric iron as shown in Fig.10.4 Construction : The main parts are i) heating element and ii) outer frame Heating element : The heating element is made up of Nichrome wire which produces heat while giving electric supply. Its melting point is about 4200 oC.
10.6 STORAGE WATER HEATERS (GEYSERS) These type of water heaters heat and store water in a tank so that hot water available to the service point (e.g., home) at ay time. As hot water is drawn form the top of the tank, cold water enters the bottom of the tank and is heated. The Storage water heaters are further classified into two types. i) Non-pressure type and ii) Pressure type Non-pressure type: When hot water is required only at one service point, this type is used.
vi) A drain value that allows us to drain the tank to replace the elements or move the tank vii) A pressure relief valve to control the water pressure inside the tank and thus keeps the tank form exploding. viii)A sacrificial anode rod to help keep the steel tank form corroding. Working : This water heater uses nothing more than the “heat rises” principle to separate hot water from cold water in the tank. When electric supply is given to the heating element, it produces heat and hence water gets heated.
10.7 REPAIRS AND REMEDIES: Complaint No hot water Causes Remedies 1. No supply. Check availability of supply at 3-pin socket 2. Blown fuse. Replace fuse 3. Open circuit. Check the wiring for broken wire or loosed connection. 4. Heater element burnt out. Check elements for burn-out Insufficient quantity of hot 1. Thermostat setting too low. water Check the thermostat setting. It Should be 60oC to 65oC 2. Lower value of heating element. Check the value of heating element and replace 3.
Leaking tank 1. Leakage around thermostat. 2. Leakage around heating unit flange. 3. Leakage at plumbing connections. Check all points for possible leakage. Replace fibre washers and use Teflon tapes to seal the leaks. 4. Tank leak. COFFEE MAKER 10.8 FUNCTION OF COFFEE MAKER : A coffee maker is a small heating appliance designed for brewing coffee from ground coffee beans without having to boil water in a separate container. 10.
Operation of coffee maker: The desired quantity of water is poured into the water chamber of the pot and the desired amount of a fairly coarse-ground coffee is placed in the top chamber. It is important that the water level be below the bottom of the coffee chamber. When the supply is given to the heating element, the temperature rises until the water in the bottom chamber boils.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. The type of heater used to heat the water contained in a plastic bucket is A) electric kettle B) immersion water heater C) storage water heater D) Any type 2.
11. ELECTRIC MIXER AND EGG BEATERS 11.1 Function of Mixie Mixer and Grinder is a kitchen appliances that facilitates task related with mixing and crushing the food. These electric machines are very much helpful as they save time and energy. There are number of attachment like blades, disc, jars etc. comes with these appliances to facilitate different uses to make the food more full of flavor and yummy. 11.2 Construction : The various parts of Electic Mixie are shown in Fig.11.
Blades: Blades are made of good quality stainless steel and will therefore give high life. Each jar will have its own blades accoring to its purpose. Jars are designed to grind dry or wet substances. So it is advisable not to interchange the blades from one jar to other. Speed control: For speed control purpose, the tapped field coils are normally employed in mixie motor. The tapped field coils as shown in Fig.11.3, enables speed selection through a rotary switch provided in the Mixie.
11.4 Caution: 1. Do not run the motor without any load. 2. The motor should not be run for more than the specifed time( prescribed by the manufacturer) 3. Do not operate unless Jar and Dome are in proper position. 4. Do not grind hot ingredients in the Mixie. 5. Do not add solid ingredients, when the Motor is running. 6. Do not add big ice pieces while making cold drinks. Crush the ice and put into the blender.
EGG BEATERS: 11.7 Function of Egg beaters: An egg beater is used not just for beating eggs, but also for whipping up cream and other ingredients. Even though there are fancy types available, sometimes a simple egg beater as shown in Fig. will be sufficient to do the job. Egg beaters are available in two forms. i) Hand Operated Crank type ii) Hand Operated Electric type 11.8 Hand Operated Crank Type: Hand Beaters are used to beat a food item or food mixture, to both mix it and introduce air.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. The drive motor used in electric Mixie is A) DC series motor B) Induction motor C) Universal motor D) Synchronous motor 2. The no load speed of electric mixie motor is about A) 3000 rpm B) 6000 rpm C) 12000 rpm D) 18000 rpm The cutting blades of electric mixie are made up of A) stainless steel B) plastic C) aluminium D) silver 3. 4.
Part - C Answer the following questions briefly (4 Marks) 1. What are the three kind of jars used in electric mixie. State the function of each. 2. How to restart the mixie if it stops due to overload? 3. How do you clean body of electric mixie, its jar and blades? 4. State the possible cause(s) and remedies when i) mixie motor is not running and ii) Excessive heat is produced 5.
12. VACUUM CLEANER AND WASHING MACHINES 12.1 Function of Vacuum Cleaner A vacuum cleaner is common household appliance used for cleaning purposes. A vacuum cleaner cleans by creating suction. A pump creates a pressure difference inside the unit causing atmospheric air to be forced up through a tubing system. Most vacuum cleaners utilize a rotating brush at its entrance to help “sweep” dust and dirt into the suction path.
pressure) increases in front of the fan and decreases behind the fan. This pressure drop behind the fan is just like the pressure drop in a straw when you drink. The pressure level behind the fan drops below the pressure level outside the vacuum cleaner. This creates suction, a partial vacuum, inside the vacuum cleaner. The air pushes itself into the vacuum cleaner through the intake port because the air pressure inside the vacuum cleaner is lower than the pressure outside.
1. To clean large floor spaces 2. For homes with thick carpets 3. As an efficient means of picking up pet hair. The traditional style of, the upright vacuum cleaner now incorporate many new features, making them more versatile. Unlike cylinder vacuum cleaners, upright vacuum cleaners are housed in an ‘all in one’ unit, and are pushed with handles that are conveniently at waist height. Large areas can be cleaned effortlessly, without having to worry about dragging the vacuum cleaner behind you.
We’ll usually need to add a cleaning solution to the wet and dry vacuum cleaner in order to wash our carpet. The dirty water is held in a container that can be emptied. Higher capacity wet containers allow for longer wash times between emptying. 12.6 Vacuum Cleaner Accessories: Vacuum cleaners usually come with a range of accessories for a variety of uses. It’s worth finding out what accessories are available for our cleaning needs.
3. If your vacuum cleaner is not sucking up the dirt effectively then it could be due to a clogged filter or hose or a moist bag. Cleaning the filter and the hose can increase the cleaning efficiency of the cleaner. If required replace the filter that will enhance the efficiency of the vacuum cleaner. 4. If there is no power supply to the vacuum cleaner then check for any discontinuity along the wire. Replace the breakers if required and mend and discontinuity along the line.
Top loading washing machine: In this washing machine the clothes are loaded and unloaded from the top of the washing machine. There is a cover at the top that helps loading and unloading of clothes in the round vessel that perform the function of the washer as well as the rinser and drier in the fully automatic washing machine. The top loading machine employs agitator type washing technique.
12.13 Working cycle: There are three cycles involved in washing process. i) Wash cycle ii) Rinse cycle and iii) spin cycle Wash cycle: This cycle involves thorough cleaning of the cloths i.e., removing dirt from cloths. This is done by moving the cloths up, down, back and forth, by means of Agitator cylinder/ Tumbler washing tub, so that the cloths get mixed well with the detergents. This motion is repeated for a determined period of time.
Drive motor: The most popular type of motor used in a washing machine is a single phase, 230 V, 50 Hz, capacitor start and run squirrel cage induction motor. These motor may range from 1/ 3 to 1/2 hp rating. These motors are normally protected from overload and overheating conditions by means of a bimetallic overload relay or a thermal switch. The motor is located in such way that water leakages do not fall on to these motors.
12.15 Basic Structure of Top loading washing machine: The complete structure showing the inner parts of washing machine are shown in Fig.12.9 The following components have to be present in any type of washing machine, be it top-loading or front-loading. Different models of machines differ only in the positioning of these parts. There is a specific function assigned to each part. 1) Water inlet control valve: Near the water inlet point of the washing there is water inlet control valve.
by means of a bimetallic overload relay or a thermal switch. The motor is located in such way that water leakages do not fall on to these motors 6) Timer: The timer helps setting the wash time for the clothes manually. In the automatic mode the time is set automatically depending upon the number of clothes inside the washing machine.
The inner tub has numerous holes. The centrifugal force pulls out wash water from the clothes and makes it move through these holes to the outer tub which stationary. The water gets pumped out from here through the drain tube. After the wash water has left, the inner tub is again filled with clean water. Agitator again works to tumble the clothing. This is the second cycle and is called the rinse cycle. The aim of this cycle is to discharge the detergent particles trapped in the washed fabric.
12.17 Comparison of Front load and Top load Washing machines: Top load - includes a wider variety of available models, colors and features as they have been on the market longer. Cost is less initially, but is less energy-efficient. Offers easier access to the wash tub. Uses regular detergent Heater facility and separate valve for hot water only on selected models Front load - people are used to seeing front load washers in Laundromats, many brands are now available for home use.
Washing Machine doesn’t Run: Recheck if the washing machine is plugged in (receiving electrical power). If it is plugged in and still does not work, then check the outlet with the VOM for the voltage and the power cord (if it is damaged). If all the devices are fine, then the lid switch or timer may have a problem. Call the appliance repair person and replace the parts if necessary. Leakage in washing machine : The leakage might take place due to damaged hoses or loose connections.
Part - C Answer the following questions briefly (4 Marks) 1. On what principle the vacuum cleaner works? Write the main components of standard vacuum cleaner. 2. Write the features usually found on vacuum cleaners. 3. State the uses of different types of vacuum cleaner. 4. What are the advantages and disadvantages of semi-automatic washing machine? 5. Compare top loading and front loading washing machine. 6. Brief the three working cycle in washing machine.
13. ELECTRIC FAN AND ELECTRIC HAIR DRIER 13.1 Function: A ceiling fan is a device suspended from the ceiling of a room, which employs hub-mounted rotating paddles to circulated air. 13.2 Terminology: The terminology mentioned in B.I.S. No. 555-1979, B.I.S. 1189-1969 and 21312-193 is reproduced here; i) ii) iii) iv) v) vi) vii) Ceiling/Table Type fan: A propeller bladed fan having two or more blades, directly driven by an electric motor, and intended for use with free inlet and outlet.
angle between starting winding and running winding current. So Capacitor is used produce required phase shift between these current and hence to produce high starting torque and will be connected in series with starting winding. Normally in ceiling fan, an electrolytic capacitor of 2.5 mF±5% will be used. The capacitor and starting winding will be in circuit during running also and hence improve the power factor. So this motor will also called as permanent capacitor induction motor.
13.4 Working of ceiling fan: The working of fan is that they do not actually reduce the temperature of the room but due the circulation and wind motion they result in surface cooling and give a breezy feeling. Electricity is used to empower the fan motors and due to the scientific design of fan blades we get the breeze, a man made phenomenon, similar to wind creation. The fan blades create a draught and the warmer air goes up. When that air is pushed down with a force, we get better air circulation.
Enclosure: The place where the fan motor is mounted may be totally enclosed type or ventilated type. The enclosure material is generally cast iron. Body and stand: The body of the table fan is usually made of die cast iron or aluminum alloy. The body is fitted or mounted to the heavy base stand, made of die cast iron or aluminum. Fig.13.5 - External parts of table fan Motor: The table fan motor is mostly of a single phase capacitor start and run or rarely shaded pole type motor.
a compression stud device. This design permits the fan to be used either as a stationary or an oscillating model. Supply cord: A 3 core, flexible sheathed conductor of length about 2 m is used which has an earthing conductor along with other two conductors. A cord grip is also inserted at the entrance point of cord into the body. Fan regulator: It is built within the table fan.
dangerous chemicals in them, exhaust fans can be used for comfort and safety. An exhaust fan is especially important when people are working with things like solvents, which are not healthy or safe to inhale. Likewise, it is important to vent fumes from paints, varnishes, and similar types of treatments. The technical data of the fan is mentioned below. Sl. No Sweep (mm) Speed (rpm) Line current Power input (Watts) Air delivery (m3/h) 1 230 1350 0.29 45 700 2 300 1400 0.
Not starting Check the voltage and adjust if possible. Low applied voltage Supply failure Condenser open or short. Check the supply points at switch, regulator ceiling rose and the terminal of the fan. Open in regulator resistor/ switch. Check for the continuity of auxillary and main winding. Open in winding. Check the capacitor with a Megger. Check for open or loose contact in the resistor or contacts. HAIR DRYERS 13.
The exploded view of Bonnet type Hair dryer is shown in Fig.13.8 below. Fig.13.8 - Exploded view of Bonnet type Hair dryer Motor driven fan: The fan should probably be called a blower; the blade is shaped like the impeller on a vaccum cleaner and mounted in a housing which is connetcted to the outlet duct. Most motors are of single speed, shaded pole motors particularly in the smaller models.
Heating element: The heating element in most hair dryers is a bare, coiled nichrome wire that’s wrapped around insulating mica boards as shown in Fig. 13.10 Nichrome wire is an alloy of two metals, nickel and chromium. This alloy is used in heating elements in a number of household products, from curling irons to toasters. Nichrome wire has two features that make it a good producer of heat: It’s a poor conductor of electricity compared to something like copper wire.
Fig.13.11 - Electrical wiring diagram of Hair dryer 13.11 Working of Hair Dryer : The working of Hair dryer is much simpler and most of its mechanisms revolve around its fan. When the dryer is switched on, the electricity moves to the windings of the motor of the fan. And here the electrical energy is transformed to kinetic energy as it provides momentum to the fan. The motor and the attached fan both spin.
Bimetallic strip - Made out of sheets of two metals, both expand when heated but at different rates. When the temperature rises inside the hair dryer, the strip heats up and bends because one metal sheet has grown larger than the other. When it reaches a certain point, it trips a switch that cuts off power to the hair dryer. Thermal fuse - For further protection against overheating and catching fire, there is often a thermal fuse included in the heating element circuit.
Unit operates intermittently. 1. Loose connections. 1. 2. Intermittent switch operation (that is it turns one time and refuses to operate the next time) 2. Unit gives no heat at any position, but motor runs. 1. Motor does not run but heater operates. 1. 2. 3. 2. 4. 5. Leads of heater open. Open in heater circuit. 1. Defective switch. Bent impeller/fan. Defective thermostat. Open circuited windings. Improper connections. 1. 2. 2. 3. 4. 5. Appliance is noisy. 1. 2. 3. 4.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. The diameter of the circle traced out by the extreme tips of the fan blades is called as A) blade flange B) blade length C) blade sweep D) blade size 2. The type of motor used in electric fan is A) capacitor start induction motor B) capacitor start and run induction motor C) shaded pole induction motor D) universal motor 3. The fan used for venting out dusty foul air is called as A) ceiling fan B) table fan C) pedestal fan 4.
Part - C Answer the following questions briefly (4 Marks) 1. Define the following terminology used in electric fan. I) Blade sweep and ii) Service value 2. Brief the construction of electric motor used in fan. 3. How is the speed of the fan controlled? Draw the schematic diagram of a fan with resistance type regulator. 4. What is exhaust fan? List its any four applications. 5. Explain briefly about the Oscillating mechanism of table fan. 6.
14. CENTRIFUGAL PUMP 14. Introduction A centrifugal pump is a machine that imparts energy to a fluid. This energy infusion can cause a liquid to flow, rise to a higher level, or both. The centrifugal pump is an extremely simple machine. It is a member of a family known as rotary machines and consists of two basic parts: 1) the rotary element or impeller and 2) the stationary element or casing (volute).
Fig.14.1 - Impeller types Fig.14.2 - Parts of a Pump Fig.14.3 - Cut section of pump casing 14.3 Working of centrifugal pump The pump is filled with liquid and the impeller is rotated. The heart of any centrifugal pump is the impeller. Fluid enters the impeller through the “eye” as shown in Fig 14.4 and is “centrifuged” (hence the name) to the impeller periphery, with assistance from the impeller vanes.
The centrifugal pump converts energy of a prime mover (a electric motor or turbine) first into velocity or kinetic energy and then into pressure energy of a fluid that is being pumped. The energy changes occur due to two main parts of the pump, the impeller and the volute or casing. The impeller is the rotating part that converts driver energy into the kinetic energy. The volute or casing is the stationary part that converts the kinetic energy into pressure energy.
Suction Lift Suction conditions are some of the most important factors affecting centrifugal pump operation. A pump cannot pull or “suck” a liquid up its suction pipe because liquids do not have tensile strength. When a pump creates suction, it is simply reducing local pressure by creating a partial vacuum (Sucks out the air above the liquid). Atmospheric or some other external pressure acting on the surface of the liquid pushes the liquid up the suction pipe into the pump.
case. This air / water separation is what makes the self primer different. Although the self priming centrifugal pump will remove all air from its suction piping, it will not “dry prime”. The pump case must be filled with water before starting. The foot valve, used at the bottom end of suction pipe should withhold water in the suction pipe. The should be no leakage of water from the foot valve. Also, there must be a way for the air to escape the discharge of the pump.
(d) Pump stops delivering after running for sometime: Leaks in the suction side especially joints. Check if sufficient water is in the well. Check motor control circuits and protection circuits. (e) Pump vibrates badly : Check alignment, bed bolts not tightened properly, impellers not properly balanced. Check for worn out bearings or bent shaft. Bearings may have excessive clearances; shaft couplings are not properly assembled. Impeller may have been choked.
4. Velocity imparted by the impeller to the water is converted to pressure by the A) Casing or volute 5. 7. 8. 9. C) Spindle D) Gland box Maximum suction lift that is possible for water is A) 24 ft 6.
Part - C Answer the following questions briefly (4 Marks) 1. What is the function of gland packing in a pump? 2. What is an impeller? State its types. 3. State the functions of casing or volute. 4. What is Friction head? 5. Define suction head. 6. Define Delivery head. 7. What is priming of the pump? Part - D Answer the following questions in one page level (10 Marks) 1. explain the constructional details of a centrifugal pump. 2.
15. MAINTENANCE OF ROTATING MACHINES 15.1 Introduction The key to minimizing motor problems is scheduled routine inspection and maintenance. The frequency of routine maintenance varies widely between applications. Including the motors in the maintenance schedule for the driven machine or general plant equipment is usually sufficient.
changing every 5000kM), This type of maintenance allows us to use the parts/equipment to the limit of their service life. Compared to periodic maintenance, predictive maintenance is condition based maintenance. Basically, predictive maintenance differs from preventive maintenance by basing maintenance need on the actual condition of the machine rather than on some preset schedule. It is possible to schedule maintenance activities to minimize or delete overtime cost.
Haly-Yearly Maintenance : 1) Clean windings of motors subjected to corrosive or other elements, also bake and varnish them, if necessary. 2) In the case of slip-ring motors, check slip-rings for grooving or unusual wear. 3) Check grease in ball and roller bearings and make it up where necessary taking care to avoid overfilling. 4) Drain all oil bearings, wash with petrol to which a few drops of oil have been added, flush with lubricating oil and refill with clean oil. Annual Maintenance 1.
and can be hazardous to the operator. Using heating equipment facilitates easy and quick removal while reducing the risk of damage to the ring and shaft. Removing bearings using hydraulic techniques. Hydraulic pressure is another available method to remove bearings. Pullers or wedges may be used to remove the bearing after the hydraulic pressure has expanded the race. Hot oil or heat may be used along with the pullers or wedges.
Frequency of Lubricating Oil Analysis Lubrication system Inspection interval Normal operating conditions Severe operating conditions Disk lubrication method One year 6 months Oil bath or splash lubrication 6 months 3 months Circulating lubrication 9 months 1 to 3 months Checking the alignment of a directly coupled motor The alignment is easily checked by laying the edge of a steel foot rule against the sides of the two flanges and checking whether the steel edge sits fully against the sides of t
turn round and come to rest with the heaviest portion in the lowest position, and the hollower portion will occupy the top position. Small counter-weights shall be fixed on the top part(lesser weight portion) of the armature. The greater the distance from the centre, the smaller should be the weight. An alternative method is to remove some weight from the heavier portion of the rotor by drilling a hole in the end supports or by chipping, as found convenient.
Check voltage of alternator at terminals and panel boards. If the generator is operating satisfactory, load the alternator gradually for 2 to 4 hours to evaporate remaining moisture. While testing it should be within 5% of rated voltage and 3 phases load should be well balanced. Always open bus bar switches and then stop the alternator. Be sure that all the switches are in ‘off’ condition before working on the equipment.
6) Measure insulation resistance. If low dry out the windings, until correct values are obtained. If necessary re-enamel or re-varnish all the winding and internal parts except the stator bore and rotor iron. Dry rotor and stator winding thoroughly. 7) Reassemble motor without using any excessive force. Make sure that machine leads are on the correct terminals and everything is well tightened. 8) Check the concentricity of the air gap through the air gap holes. Ensure that rotor can rotate freely.
Single Phase Motors: Centrifugal (CF) switch is one of the main cause of troubles in single phase motors. If the springs of centrifugal switch become weak, the C.F. switch will operate before reaching the full speed, which will cause motor to run at sub normal speed and stop. If the switch sticks closed, the starting winding will remain in the circuit, overheat and damage the starting winding. Commutator motors need almost same type of care and maintenance as in dc motors. 15.
The insulation resistance should be measured when motor is hot, whenever possible. The reason is that even a damp winding will give a comparatively higher reading if taken when cold and therefore such a reading is unreliable. The reading will be lower when taken ‘hot’. As already stated, the resistance of any insulation falls as the temperature rises, which is directly opposite to that of any metallic conductor the resistance of which rises as the temperature rises.
Care in fitting a new carbon brush The surface of each carbon brush should be carefully ground to correspond to the curvature of the commutator so that the brush makes contact over its full area, so as to be able to carry the full load current. The correct curvature is ensured by drawing a strip of very smooth sand paper under the brush and over the commutator or the slip ring. It should be moved to and fro in close contact with the commutator surface.
Table 15.2 Trouble Shooting chart - D.C. Machines S. No Symptom Possible Cause of Trouble Remedy 1 Failure to build up of voltage (dc generator) Faulty Voltmeter, check output voltage with separate voltmeter. Open field resistor. Replace voltmeter. Replace or repair resistor Open field circuit. Check coils for open circuit or loose connections. Replace defective coils, tighten or solder loose connections. Absence of residual magnetism in self excited generator. Flash the field.
3 Output voltage too high (dc generator) Field resistor not properly adjusted Reversed field coil or armature coil connections Adjust governing device. Adjust or replace faulty voltage regulator. Check speed. Prime mover speed too high. Faulty voltage regulator Overloaded. 4 Armature too hot Check meter readings against name plate rating. Excessive brush pressure. Belt too tight, or coupling not aligned. End plate out of position. Bent shaft. Armature coil shorted Armature striking poles.
6 Sparking at brushes Brushes off neutral plane. Brushes not seated properly. Dirty brushes and commutator High mica, Rough or eccentric commutator. Open in armature Grounded, open or shorted field winding Lack of brush pressure; brushes sticking in holder Selective commutation caused by unequal brush tension Open circuit Rheostat in field Set rigging so that brushes are in proper plane. Reset. Clean. Under cut; Resurface commutator, Repair/ replace armature. Repair or replace defective coil/coils.
iii) Commutator is eccentric or having high bars and low bars : Excessive blackening or burning of a few commutator bars only shows presence of high or low bars, mostly caused by the bolts holding the commutator V-ring becoming slack. The bolts should be tightened up fully, after the commutator has run in for some time and is fully warm. After this is done, the commutator should be skimmed on a lathe.
tank, are easily removed periodically from a drain outlet. 15.15 Applying insulating varnish on electrical coils and windings Coils are made up of insulated wires, the covering consisting of cotton, silk or enamel, etc. which are hygroscopic, i.e. they tend to absorb and retain moisture. The insulation provided between layers as well as the space between turns in the interior of the coil contain considerable amount of air spaces.
QUESTIONS Part - A Choose the Correct Answer (1 Mark) 1. The maintenance work carried out on the machine after it has failed to work is called A) Breakdown maintenance B) Preventive maintenance C) Periodic maintenance D) Predictive maintenance. 2. If air gap shows variation in the top, bottom sides, it is due to A) bent shaft B) Lamination worn out C) Worn out bearings D) Rotor worn out. 3. Best method of removing a bearing is by using a A) Hammer B) Chisel C) Caliper D) Bearing puller 4.
Part - B Answer the following questions in one or two words (1 Mark) 1. Which type of maintenance is called as a daily maintenance procedure? 2. What maintenance procedure is based on inspection or diagnosis? 3. How the air gap is measured in electric motors? 4. Which type of puller is more safe for bearing removal? 5. What type of fit does the cylindrical roller bearings have? 6. What is the inspection interval for Circulating lubrication system under normal operating conditions? 7.
Part - D Answer the following questions in one page level (10 Marks) 1. What are the necessary actions to be taken during daily maintenance of motors? 2. Explain how predictive maintenance is carried out? 3. Explain the procedure for static balancing and dynamic balancing? 4. Identify the causes for insulation value becoming lower. What are the steps needs to be taken to avoid it? 5. What is degreasing? How it is done? 6.
16. MAINTENANCE OF TRANSFORMERS 16.1 Introduction The transformer is one of the most reliable items of electrical equipment, requiring relatively little attention; yet often even the minimum of attention is not given, they also sometimes breakdown because of neglect. The programme of inspection and maintenance is governed by the size of the transformer, place of installation, whether indoors or outdoors, if in a substation is it manned or unattended, the operating conditions and so on.
16.4 Different methods of drying out a transformer : The main problem in drying out a transformer is not drying the oil- this is quite easily done by passing it twice or thrice through a suitable filter- it is the removal of moisture absorbed by the windings. This is quite a time consuming process in a new transformer to be commissioned for the first time, and may last from a few days for a small transformer to 3 or 4 weeks for a large unit.
N.B. Application of vacuum greatly accelerates the drying-out process. Vacuum may be applied directly into the transformer tank by connecting a vacuum pump producing at least 28 in. of vacuum, through a suitable outlet, provided that the tank is specially designed to withstand the full air pressure (15lbs/sq. in.) on the exposed surfaces of the tank. Alternatively vacuum type purifiers should be used. 16.
of metal surfaces. If acidity content becomes excessive in service, the oil should be replaced with new oil. vi) ’Flash’ point and ‘Pour’ point should be as per specifications laid down. vii) It should be chemically stable, i.e. it should not react to oxygen in the air even at high temperatures. 16.7 Different methods of purifying and drying-out transformer oils : There are primarily three types of oil purifiers in common use: i) Centrifugal purifiers such as the ‘De Laval’ type.
ii) The test should be conducted when the oil is cold and not when hot. The dielectric strength varies with temperature as shown below : Temperature 0C 30 40 50 60 70 80 BDV, kV 33 35 36 37 38 39 iii) Rubber is affected by oil. Therefore use plastic tubes for drawing out the sample. Sampling bottles should have glass stoppers; cork absorbs moisture and may contaminate the oil. iv) The sample of oil should preferably be drawn from the bottom of the transformer tank.
Fig.16.1 - Transformer oil testing kit c) A circuit breaker to trip off the supply to the transformer, immediately if a sparkover occurs. (vii) The actual testing is done as follows : a) The gap is first checked with gauge and the test cup and the electrode gap thoroughly cleaned and washed with oil known to be good. The cup is then filled with the sample oil to be tested upto about one cm above the electrodes.
consider before collecting a sample. The ideal situation for collecting a sample from an electrical apparatus is 35°C (95°F) or higher, zero percent humidity and no wind. Cold conditions, or conditions when relative humidity is in excess of 70 percent, should be avoided, as this will increase moisture in the sample. Collecting a sample during windy conditions is also not recommended because dust and debris enter the clean sample easily and disrupt accurate particle counts.
outgoing lines, which should be traced and rectified; if it does not blow the fault or overload has apparently cleared itself. If,on the other hand, the primary circuit fuse blows out, even when the load is disconnected, an internal fault or a fault in the connecting cable is indicated. The above remarks also apply,if an over-current relay alone has operated and tripped the breaker. iii) If a differential relay operates when a transformer is first switched on, it may be due to a switching surge.
cleaned of all accumulated sludge, muck and dirt. Take care to clean up the drain plug, and wash the interior of the tank as well as the cooling tubes, first with old oil and again with new oil. If there are any cracked or badly welded joints they may be attended to. Thoroughly clean all the gasket surfaces and keep new gaskets ready. Check acidity of oil, if excessive replace it by fresh oil. Sludge to be removed from the core and coil assembly .
3. Drying process can be quickened by applying A) Heat B) Hot air C) High pressure D) Vacuum. 4. A simple and quick way of checking moisture in transformer oil is A) Crackle test B) Di-electric test C Break down test D) Flash test 5. A gap of ________________ mm is maintained between the spheres in the dielectric strength testing kit. A) 1 mm B) 2.5 mm C) 4 mm D) 10 mm 6. The dielectric strength of oil should be ________________ kV for 1 min. under normal condition of oil.
10. What is the very important aspect to be observed while of conducting dielectric strength test on transformer oil? Part - C Answer the following questions briefly 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.
HIGHER SECONDARY - VOCATIONAL THEORY - ELECTRICAL MACHINES AND APPLIANCES MODEL QUESTION PAPER Time: 3Hrs Max. Marks: 200 Part – I Choose the Correct Answer 15x1=15 Marks 1. Insulating materials are used between A) Conducting materials and Non - conducting materials B) Two non –conducting materials C) Two-conducting materials (both not part of current carrying circuit) D) Two conducting materials (of which only one is part of current carrying circuit) 2.
13. The diameter of the circle traced out by the extreme tips of the fan blades is called as A) Blade flange B) blade length C) blade sweep D) blade size 14. The part due to wich water gets the centrifugal force is called A) Casing or volute B) stuffing box C) spindle D) impeller 15.
Part – III Answer Any ten Questions in one or two sentences 10x4=40 Marks 31. Give two examples of insulating materials in each of the above classes. 32. What is meant by flexible wire? 33. What are called as half coil windings? 34. Calculate the angle between the adjacent slots for a 3 phase, single layer concentric type of winding for a 2 pole ac machine having 12 slots. 35.
Part – IV Answer Any Four Questions Elaborately 4x20=80Marks 50. Derive expressions for electrical and mechanical degrees in terms of poles and slots. 51. Develop a 3 phase, single layer concentric type of winding for a 4 pole ac machine having 24 slots using a) Half coil winding OR b) whole coil winding OR c) mush winding 52. Develop a winding diagram for a 4 pole, 13 slot double layer simplex wave connected dc machine with 1 commutator segments. Indicate the position of brushes. 53.
194 1 15 15 Details of winding Development of Winding - AC machines Development of Winding - DC machines Rewinding and Testing of Electric motors Instruments and Testing Electrical Cooking Appliances Electric Iron Box Water Heaters and Coffee Makers Electric mixer and Egg Beaters Vacuum cleaner and Washing machines Electric Fan and Electric hair drier Centrifugal Pump Maintenance of Roatating machines Maintenance of Transformers TOTAL QUESTIONS TO BE ANSWERED TOTAL MARKS - 200 3. 4. 5 6.
