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International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 Design of 215kW DC Motor for Centrifugal Machine Used in Sugar Mill (IJSETR) Sis Sis Soe Abstract— In designing the DC machine with appropriate performance characteristics, it is essential that the designer is fully conversant with the typical performance of the machine that is needed to improve the design of DC motor. The field of direct current usage being very wide, DC machines is produced both as generators and motors for a large range of output, voltage, speed etc. DC motors offer many distinct economic and technological advantages in special application like rolling mills, overhead cranes, lifts, electric vehicles and electric trains. The DC motor basically works on the principle that when a conductor carry current is placed in a magnetic field, mechanical force acts on the current carrying conductor, as a result the conductor starts rotating in a direction depending upon the direction of current and the field is given by Flemings’ left hand rule. The e.m.f induced in the armature of alternates with a frequency of f, Hz depending upon the number of poles in the machine and the speed of the armature. Index Terms—400V DC Supply, Compound DC Motor, Design Calculation, Sugar Mill II. SUGAR MANUFACTURING PROCESS A sugar mill is a large factory used to produce raw sugar and other products from sugar cane. Mills are made up of a range of industrial plant such as boilers, storage and processing vessels, crushing and hammer mills and a large range of maintenance equipment. Mills operate in two distinct modes, crushing and non-crushing, both of which introduce a range of specific and general hazards to PCBUs, workers and others. In essence, a sugar mill can be broken into the following processes (see Fig. 1, for a diagram that shows the sugar milling process). Sugar manufacturing process consists of; 1. Cane handling (Preparation of Sugarcane) 2. Milling house 3. Clarification and evaporation 4. The pan stage 5. The fugal stage 6. Final sugar 7. Energy supply systems 8. Associated operations I. INTRODUCTION DC motors comprise one of the most common types of actuator designed into electromechanical systems. They are a very straightforward and inexpensive means of creating motion or forces. Electric motors are an essential component of our industrial society with no less than 5 billion motor, built world wide every year. The most wage two types of motor are AC motor and Dc motor. DC motors are widely used in many industrial applications such as electric vehicles, steel rolling mills, electric cranes, and robotic manipulators. The direct current motor is one of the first machines devised to convert electrical power into mechanical power. When a conductor carrying current is placed in a magnetic field, force is developed in the conductor. If a number of conductors connected in series are placed on a cylindrical rotor and current is allowed to flow through the conductors, a torque will motor, two magnetic fields can be found, i.e. the field produced by the magnets and the field produced by the current flowing through the armature conductors. DC motors are classified such as shunt motor, separately excited motor, series motor, compound motor, permanent magnet DC (PMDC) motor and so on. AC motors are divided into two groups such as induction motor and synchronous motor. In this paper we are designed for the compound DC motor for the use of centrifugal machine at fugal stage. Figure.1. Raw and Refined Sugar Process A. Cane Handling The main objective of cane preparation is shredder from the cane with the help of machine power before milling to the smallest cane chip and which is sending with preparation to cane milling. Thus, this smallest cane chip can be milled from milling machine one to milling machine four and get not only more juice but also good mill extraction for factory. The main ambitions of cane preparation are 1. To increase in bulk density 2. To increase in crushing capacity Manuscript received Oct 15, 2011. Sis Sis Soe, Deperment of Electrical Power Engineering, Mandalay Technological University, (e-mail: [email protected]). 3. To improve in pol extraction 4. To improve in primary juice extraction 1 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 5. To perform proportion load on mills 6. To obtain higher efficiency of imbibitions 7. To reduce in hydraulic pressure and thus less power consumption 8. To reduce wearing of mill rollers The followings are used for cane preparation 1. Cane feed table 2. Cane carrier 3. Cane leveler 4. Cane knives (cane cutter) 5. Magnetic iron separator 6. Cane shredder 7. Elevator B. Milling House The milling process essentially involves the removal of juice from sugarcane by squeezing the cane between pairs of large cylindrical rolls in a series of milling units collectively called a milling train, as show in Fig. 2. The first milling unit in the milling train is generally identified as #1 mill; the second milling unit is generally identified as #2 mill, and so on. The last milling unit is generally called the final mill. The milling units between the first and final mills are collectively known as intermediate mills. After passing through a pair of rolls and expressing juice, the remaining sugarcane material is known as bagasse. Only the first milling unit in the milling train processes prepared cane. The remaining milling units process bagasse. After being processed by a mill, bagasse typically consists of 30% to 50% of fiber, 45% to 60% of water and a diminishing quantity of brix as subsequent milling units process the bagasse. Although prepared cane and bagasse are defined as different materials, bagasse as a general term to collectively refer to both prepared cane and bagasse. water or juice added to the bagasse is called imbibitions process, called compound imbibitions, is shown in Figure 3. Imbibition water is added to the bagasse entering the final milling unit at a rate that is typically 200% to 300% of the rate of fiber passing through the milling train. The juice expressed from the final milling unit is used as imbibition juice for the second last milling unit. The juice from the second last milling unit is then used as imbibitions juice for the third last milling unit. This process continues back to the second milling unit. After first passing through a juice screen to remove most of the fiber in the juice, the juice from the first and second milling units, called mixed juice, is taken away for processing into sugar. The fiber removed in the juice screen, called cush, is returned to the milling train, usually before the second milling unit. The bagasse from the final milling unit is taken away for further processing, typically for burning in the boiler furnace. C. Fugal Stage A fugal is a large electric centrifuge which spins up to 1200 revolutions per minute dependent on its function and stage of operation. There are two types of centrifuge in use within sugar mills, high grade centrifuges (usually batch, but sometimes continuous) and low grade centrifuges which are continuous. Continuous fugal maintain a constant flow of product through them while batch fugal fill, operate and then discharge the final product. The fugal stage removes the remaining liquid product which surrounds the crystal, washes the crystal and delivers it into the final sugar system through a series of conveyors and a drier. The material removed during the centrifuge process is known as molasses and has a range of uses including sale as stock feed, fermentation for distillery production and as a component of cattle licks. D. Electric Motor Used in Sugar Mill At sugar mill, electric motors are used for cane feed table, cane carrier, cane leveler, cane knives, magnetic iron separator, cane shredder, cane elevator, mill tandem and centrifugal machine. The electric motors used for sugar mill are wound-rotor induction motor with slip ring, squirrel-cage induction motor and DC motors such as separately excited motor, shunt motor and series. Especially, compound DC motors are used for centrifugal machine at fugal stage. III. COMPOUND DC MOTOR Compound motors are a combination of series and shunt motors. A compound motor has two field windings, one is a series with the armature winding, and which is therefore made of thick wire of few turns. The second winding is called the shunt field winding and is joined in parallel with the armature and is made of thin wire of many turns (Figure.3). The series field winding is wound above the shunt field winding on the same pole shoe. In a compound motor the major portion of the flux is produced by the shunt field winding. Figure.2. Schematic diagram of milling train To aid in the extraction of juice from the much drier bagasse, water or diluted juice is added to the bagasse before it enters the milling unit in a process called imbibition. The 2 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 loadings before the derivation of output equation. For the specific magnetic loading, equation (1) is used and for the specific electric loading, equation (2) is used. For number of conductors, equation (3) is used and derivation of output equation, equation (4) is used. For gross length of armature and armature resistance, equations (5) and (6) are used. Equations (7) to (21) are used for resistance of winding, flux frequency reversal, speed, electromagnetic torque and efficiency of DC motor. A. Design of Armature Winding pφ B av Figure.3.Connections of a compound motor There are two types of compound motors according to the manner in which their field windings produce field flux; 1. Differential Compound Motor, and 2. Commulative (or addative ) Compound motor IV. DESIGN THEORY As compared to rotating machine, the design of DC motor is simpler, because of complex inter relations between magnetic and electric circuit. The aim, in designing the DC machine is to obtain the complete dimensions of various parts of the machine as lute below, to furnish these data to the manufacturer. 1. Main dimensions of the armature structure 2. Design details of the armature winding 3. Main dimension of the field system 4. Design details of the field winding 5. Design details of the commutator and brushes 6. Design details of inter poles and its winding 7. Performance characteristics i.e. iron losses copper losses, mechanical losses, efficiency and maximum efficiency In order to determine the above design information, for the DC motor, designer needs the following. 1. Detailed specification of the DC motor 2. Limiting value of performance characteristics like iron losses, copper losses, efficiency 3. Design equation based pm which design procedure is to be initiated 4. Information regarding availability of material for various parts The above information needed to carry out the design has been discussed in subsequent articles. Hence the design of DC motor is carried out based on given specifications, using available materials economically and to achieve lower cost, reduced size and better operating performance. Important specifications needed to initiate the design are given below (input design data). Type of field excitation; rated output power; rated output voltage; speed; type of enclosure; type of duty (short time, inter mitten, continuous); field excitation voltage; maximum temperature rise. After that we can draw good design and we can construct efficiency good DC motor for our load. V. DESIGN EQUATION OF DC MOTOR Design equation expresses the relationship between the output of the machine and the main dimension of the armature in terms of specific magnetic and electric loadings. It is essential to define the terms specific magnetic and electric (1) πDL Where, B = Average gap flux density, Tesla P= Number of poles Ø= gap flux per pole, Wb D = diameter of armature, m L = gross length of armature, m av Ia Z A q (2) πD Where, q = specific electric loading I = armature current a E PZN (3) 60 A Where, E = supply voltage, V N = number of speed,r.p.m Z = number of conductors A = number of parallel paths Pa E a I a 10 3 (4) Where, Pa = output power Pa 1 2 D L Co N (5) Where, C0 = output coefficient=0.164Bavq×10-3 πD L Kp P Where, Kp = ratio of pole arc and pole pitch Ra ρL c Z ac 1 2 A Where, ρ = resistivity of material, ohm-mm2/m Lc = length of conductors, m ac = cross sectional area of conductor, mm2 NP f 120 Where, f = flux frequency reversal, Hz (6) (7) (8) 3 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 N Eb Kφ (9) Where, Eb= induced voltage K = constant φ = flux per pole of motor, wb Where, θ =temperature rise of field system Pf=losses of field system per unit cooling surface, W/cm2 vA=peripheral speed of armature in m/sec C. Design of Commutator and Brushes πD S (10) θ slot pith Where, S= number of slots Di=D-2hs-2dc Where, Di=internal diameter of armature hs=depth of slots dc=depth of armature core θ (11) 120 lossesin W/cm 2 (18) 1 0.1Vc Where, θ =temperature rise of commutator vc=peripheral speed of commutator load current ' Ib pair of po le 250 to 300 p (12) 1 0.09 VA1.3 Where, Ib′=current per brush Nb Where, θ =temperature-rise of armature P′=total armature iron and copper losses per sq.cm of the cooling surface, w/cm2 vA=peripheral speed of armature, m/sec (19) ' Ab (20) Ab Where, Nb=number of brush per spindle Ab′=total brush area per spindle Ab=area of brush B. Design of field Winding R sh η ρL mtf Tsh a sh (13) Where, Lmtf = mean length of the turns of shunt exciting coil Tsh = total turn of shunt field winding Ash = cross sectional area of conductor ATf Tsh I sh Ap (14) (15) Lp Where, ATse= ampere turn of series winding Ise = armature current, Ia 1400 to 1600 p f θ 1 0.07 VA 100 (21) Where, η = efficiency Design results can get as shown in table (2) by using input table (1) and specific magnetic loading equation (1), specific electric loading equation (2) and output power equation (4) and equations (5) to (21).To calculate the proper size with input data rating, gap flux density, core flux density and specific electric loading are assumed. Note that every flux density values never exceed 2.2 Tesla. One DC motor can get good efficiency by making starting torque may be rise to higher value. The main important fact is to reduce m motor losses. TABLE I INPUT DATA Where, Ap = gross area of pole Lp = axial length of the pole I Z ATse 0.15 to0.2 a 2P output losses VI. DESIGN RESULTS Where, Tsh = total number of turn ATf = total ampere turn of the exciting coil Ish = shunt field current bp output (16) Specifications Symbol Unit Design Value Motor output Po W 215×103 Terminal voltage V V 400 Speed Type N - r.p.m - 1200 Compound (17) TABLE II DESIGN RESULTS 4 All Rights Reserved © 2012 IJSETR International Journal of Science, Engineering and Technology Research (IJSETR) Volume 1, Issue 1, July 2012 Specifications MAIN DIMENSIONS -Armature diameter -Gross Length -Peripheral speed -Flux frequency -Pole pitch -Flux per pole ARMATURE WINDING -Type -Total armature conductor -Number of slots -Conductors per slot -Resistance of winding -Armature copper loss FIELD SYSTEM -Axial length of pole -Breadth of pole -Height of pole SHUNT WINDING -Cross sectional area -Exciting current -Number of turns -Resistance -Copper losses SERIES WINDING -Ampere turns -Current -Turns per pole -Resistance -Copper losses INTER POLE WINDING -Ampere turn for inter pole -Turn on each inter pole -Cross sectional area -Depth of winding -Resistance -Copper losses OVERALL PERFORMANCE -Armature copper losses -Series field copper losses -Interpole winding copper losses -Shunt field copper losses -Iron losses -Commutator brush contact loss -Commutator brush friction loss -Bearing friction and windage loss -Total full load losses -Full load efficiency -Tem. rise of armature -Tem. rise of commutator Design Value VII. CONCLUSION Symbol Unit D L VA f τp φ m m m/sec Hz m wb 0.48 0.247 30 40 0.377 0.0577 Z S Zs ra Ia2ra ohm kW Lap 336 58 6 0.0116 4.13 Lp bp hp m m m 0.232 0.198 0.23 ash Ish Rsh - mm2 A ohm kW 1.31 2.2 2402 147 0.711 ATse Ise Rse - A ohm kW 1194 597 2 0.00059 0.210 ATcp - 7729 acp dcp Rcp - mm2 cm ohm kW 13 260 2.1 0.00166 0.593 [1] - kw kW kw 4.96 0.210 0.596 [7] - kw kW kw 0.711 3.052 1.184 - kw 1.013 - kw 2.15 η θ θ kW % °C °C 13.876 93.9 39 13.6 This paper deals with main design of DC motor used in sugar mill and study of the various functions of DC motor. DC motor is composed of two main parts such that field winding and armature section. All designers can make proper design and construct DC motor for milling train. When this compound DC motor to compare with other motor, it can more produce high starting torque in short time to reach maximum value than other motors. The series field provides better starting torque and the shunt field provides better speed regulation. To choose motor, 400V supply voltage compound DC motor is the most suitable DC motor for centrifugal machine used in sugar factory. ACKNOWLEDGMENT Firstly, the author wishes express her deep gratitude to His Excellency Union Minister Dr. Ko Ko Oo, Ministry of Science and Technology, for opening the Special Intensive Course Leading to Master of Engineering at Mandalay Technological University. The author would also like to thank Dr. Myint Thein, Rector of Mandalay Technological University for his motivation, supports and guidance. The author would like to express her heartfelt gratitude to her Supervisor U Thet Naing Htun, lecturer of Mandalay Technological university, for his kind advice, permission and his encouragement throughout this paper. His valuable suggestions have been greatly appreciated. The author also greatly thanks to Dr. Khin Thuzar Soe, Head of Department of Electrical Power Engineering of Mandalay Technological University for her support and encouragement through out this paper. After that the author always thanks all teachers from Electrical Power Engineering Department because of their guidance, encouragement and advices and suggestions. REFERENCES [2] [3] [4] [5] [6] Charles L. Hubert, “Electric Machine, Theory, Operation, Application, Adjustments, and Control” A.E. Fitzgeralad, “Generalized Theory of Electrical Machines” Mark A. Juds, Earl F. Richards and Willion H. Yeadon, “Hand book of Small Electric Motor” Mandalay Technological University, “Electrical Machines, 1999” Dr V. N. MITTLE, “Design of Electric Machines” Geoffrey Alan KENT, “Increasing the capacity of Australian raw sugar factrory milling units, 2003” Allbest Creative Development Ltd. (ALLBEST), “Sugar Mill”, Beijing, China 5 All Rights Reserved © 2012 IJSETR