Three-Phase Induction Motor Preliminar Design Assisted by CAD Software based on Brazilian Standards

Transcription

1 Three-Phae Induction Motor Preliminar Deign Aited by CAD Software baed on Brazilian Standard Victor de Paula Brandão Aguiar 2, Ricardo Silva Thé Ponte, Tobia Rafael Fernande Neto Department of Electrical Engineering, Federal Univerity of Ceara 2 Department of Environmental and Technological Science, Federal Rural Univerity of Semi-Arid Abtract Energy efficiency of electric motor i a challenge for the national indutry in many countrie, although their efficiency ha been increaed gradually over the year. Thi paper deal a computer-aided tool for the deign of N-type (imilar NEMA B-type) three-phae Induction Motor (IM). Such tool will bring flexibility for the deign engineer during the project development. The oftware ha the following main objective: ) to analyze the input data parameter of the IM project, according to Brazilian technical tandard (NBR) 7094-:2008 and 5623-:2008, printed by the Brazilian Standard Organization (ABNT); 2) to deign an IM with all electrical pecificity, baed on a known project method; 3) to evaluate the deigned motor performance with the ame methodology. The program ha a friendly graphical uer interface (GUI) and it wa developed by uing the GUI development environment tool from MATLAB. Thi paper alo decribe the logic programming through flowchart and equation. The oftware main purpoe i to produce a computer-aided tool for deigning IM at the firt conception tep. It will evaluate the performance of the project (no built) and eek alternative to improve it efficiency before the motor` aembly. Knowing that the Brazilian tandard requirement induce to achieve higher level of efficiency (equivalent for other national tandard) in an IM deign, their technical feature will be taking into account, and probably it may change the previouly ued IM deign method. Change on the methodology hall be highlighted in the paper.. Introduction The energy efficiency of electric motor i one of the bigget challenge for the national indutry in everal countrie, e.g. Brazil, USA and EU countrie. In recent year, thee countrie have reviewed the minimum efficiency level of motor [] [2] [3], believing in the gradually increae of energy efficiency, which are already hown experimentally in [4] [5] and alo theoretically [6]. It i oberved in thi challenge the opportunity to improve the deign tool, commonly ued in an electric motor deign. Brazilian tandard require ome neceary value for the induction motor deign, a well a NEMA and IEC tandard. Thee tandard deal with the input parameter to be pecified at the beginning of the deign, uch a: rated voltage, ervice factor, inulation cla [7], minimum or maximum value like: torque, tarting torque, caing (frame type), relation between the tarting apparent power and rated power [8] and the minimum efficiency level [3] [9]. The propoed oftware evaluate the deign proce during ome of thee limiting deign parameter, not for all, but the ufficient to achieve the main purpoe of the deign engineer. The oftware wa developed in MATLAB and it fulfill the analytical approach of induction motor deign, uing the already known technique preented in [7]. The oftware doe not verify the typical parameter value like: flux denity and current denity, uually verified in numerical technique uch a finite element or other. The motivation of thi work i to provide a tool, which can carry out a fat evaluation, but not necearily the final olution to the project [0].

2 2. Brazilian Technical Standard The main Brazilian tandard which have importance in the induction motor deign are the tandard decribed in [8] and [9]. In [9] are preented the tandard dimenion for rotary electrical machine, like: the relation between the frame ize and the height of end haft (H), the diameter of the rotor haft and the recommended rated power in kw. The relation between the frame ize and the height of end haft (H) i preented on [9]. Among the tandard horepower rating of electrical motor in the range from hp to 50 hp, the recommended power rate are 0.75 kw ( hp),. kw (.5 hp),.5 kw (2 hp),.8 kw (2.5 hp), 2.2 kw (3 hp), 3 kw (4 hp), 3.7 kw (5 hp), 4 kw (5.5 hp), 4.5 kw (6 hp), 5.5 kw (7.5 hp), 6.3 kw (8.5 hp), 7.5 kw (0 hp), 0 kw (3.5 hp), kw (5 hp), 3 kw (7.5 hp), 5 kw (20 hp), 7 kw (22.8 hp) 8.5 kw (25 hp), 20 kw (26.8 hp), 22 kw (30 hp), 25 kw (33.5 hp), 30 kw (40 hp), 32 kw (43 hp) and 37 kw (50 hp). It i important to point out that the table recommend power rate value up to 000 kw (340 hp). The tandard haft diameter have the following value in mm: 7, 9,, 4, 6, 8, 9, 22, 24, 28, 32, 38, 42, 48, 55, 60, 66, 70, 75, 80, 85, 90, 95, 00 and 0. In [8] are preented, the motor duty cycle (S to S0, where S i the continuou duty), the upply voltage (220 V, 380 V or 440 V), the upply frequency of 60 Hz for product to be commercialized in Brazil, the motor deign (N, H and D), which i imilar to NEMA motor deign (B, C and D), minimum value for tarting torque (in pu), locked rotor KVA (limit for inruh current) and maximum torque (in pu). The minimum tarting torque and maximum torque are function of the rated motor power, the number of pole and the motor deign (N, H). For the motor deign D, it i tandardized only the tarting torque at a fixed value of 2.75 pu. The locked rotor KVA i given by the following expreion, where S p i the tarting apparent power, Pn i the rated power, Ip I n i the tarting current in pu, i the efficiency at full load and PF i the power factor at full load. The tandard how the maximum value for the ratio Sp P n (only for the motor deign N and H), depending on the motor rated power. S p I p In P FP n () The tandard ditinguihe the motor with tar/delta tarter (NY and HY). Thee motor feature the ame characteritic given for the categorie N and H. The only the tandard recommendation i that the tarting torque in pu hould have 25% of the value for categorie N and H. Moreover, the mechanical load hould be reduced, ince the tarting torque could be inufficient for it own tarting. The tandard pecifie when and how the ervice factor hould be different than one (). If the motor deign project agree with the riing temperature limit of the tandard, they mut have the unit ervice factor (=). Otherwie, it i neceary to pecify a ervice factor greater than one (>). For electric motor with the power rate from 0.75 kw ( hp) to 50 kw (200 hp), the ervice factor it can be modified to.5. Fractional motor vary thi modification between the value of.5 and.4. In cae of a higher overload capability, it i recommended to ue a tandardized motor with a rated power higher than the original. In [8] i diplayed, the minimum efficiency level for induction motor. The value are tandardized according to the motor rated power and it ynchronou peed. One ection of the tandard table i hown in Figure. The recommendation of the reference temperature for the appropriate inulation cla (temperature correction of reitance) i alo tandardized, even if there are no reference on thi temperature in high-efficiency motor. The tandard alo provide a match between the frame ize, the rated power and the machine ynchronou peed. Thi correpondence i retricted to induction motor IP44, IP54 or IP55, thermal cla B or F, motor deign N, 60 Hz frequency, low voltage and height of end haft between 63 mm and 355 mm, in continuou duty. 2

3 Figure Relationhip between rated power, ynchronou rotation peed and frame ize [8] 3. Deign Methodology for Induction Motor The ued deign methodology i decribed in [7]. The deign algorithm i hown in Fig Stator core izing Thi methodology i baed on output coefficient deign concept, which give the inner tator diameter calculation ( D ). i D i 3 2 p p KEPn C f PF 0 (2) Figure 2 Deign algorithm [7] 3

4 For equation 2, it i neceary to define the number of pole pair ( p ), the ratio between the tack length and the pole pitch ( ),the Eon contant ( C 0 ), the emf coefficient ( K E ) and the input parameter ( P n, PF, e f ). The Eon contant i a function of the number of pole, the apparent power. From the teeth aturation coefficient ( Kt ), the voltage form factor ( K f ) and the flux denity hape factor ( i ) are pecified. Together the winding factor ( K w ) and the airgap flux denity ( B g ), determine the pecific tator current load ( A ). A C 0 2 K f i Kw Bg (3) With all the above calculated value, other tator etting are required uch a: the deign current denity ( J co ), the lot fill factor ( K fill ), the tooth flux denity ( B t ), tator back iron flux denity ( B c ) tator lot height ( h ), the core radial height ( h c ) and finally the outer tator diameter ( D out ). For tator lot izing, it hould be computed the tator lot opening ( b o ), the height of the tator lot opening ( h o ), the wedge height ( h w ), the lot upper width ( b 2 ), the lot lower width ( b ) and the tooth width ( b t ). The tooth width, for manufacturing reaon, hould not be le than 3.5 mm. Thi lot i called emi cloed trapezoidal lot. 3.. Stator winding Knowing the number of tator lot ( N ) from the number tator lot per pole ( q ), the winding type (double layer chorded winding or ingle layer) i defined. The calculation of the number of turn per lot i given in the following: KE V ph W 4 K K f f w g (4) where ( V ph ) i the phae voltage and ( g ) i the air-gap flux. The number of conductor per lot ( n ) i given by: n aw p q (5) where ( a ) i the number of path in parallel, uch parameter may be a. Therefore, the magnetic wire cro ection i calculated from the rated current ( I n ) A co I a J n co (6) 3.2 Rotor core izing For the number of rotor lot ( N r ) hould be choen avoiding the alignment between the rotor and tator teeth, thu minimizing the reluctance torque. The deigner' expertie i very important at thi 4

5 moment. In general the number of tator lot mut be different from the number of rotor lot. The rounded emi-cloed rotor lot can be found high efficiency motor. [7] Since the magnetomotive force (MMF) in the tator and rotor do not have equal magnitude, it i poible to calculate the value of rotor bar current ( I b ) from a relationhip between the mmf of the rotor and the tator. K I FMM r Ib Nr 0.8 PF FMM 2mW K I w n (7) From the rotor bar current, the end ring current can be computed ( I er ), and with the current denity in the rotor bar ( J b ), the rotor lot area i determined ( A b ). Linking the end ring current with the current denity in the end ring ( J ), we obtain end ring cro ection. er A b, er I b, er (8) J b, er The deign i accomplihed by calculating the air gap length ( g ) (hould not be le than 0.35 mm for manufacturing reaon [7]), rotor diameter ( D re ), the rotor tooth flux denity ( b tr ), the upper lot diameter ( d ), the lower lot diameter ( d 2 ), lot height ( h r ),the height of the rotor lot opening ( h or ) and rotor lot opening ( b or ). 3.3 Application of Brazilian tandard in deign methodology Figure 4 how the moment where the generated deign data will be handled by the Brazilian tandard requirement. Figure 3 Deign algorithm taking into account the highlighted requirement of the Brazilian Standard 5

6 The tep number five (ee Fig. 4) i related to motor performance and ue the IM equivalent circuit with calculated parameter from the deign data [7]. After the calculation of the equivalent circuit parameter, locked rotor KVA, efficiency, locked rotor torque, breakdown torque and the riing temperature are checked. 4. CAD (Computer Aided-Deign) Software The developed oftware ha a equential imple and tructure, where the tep are decribed in flowchart in thi ection. The firt flowchart hown in Figure 4, preent the firt part of the oftware that i the verification of input data by ome requirement hown in ection 2. Figure 4 Standard input data verification In Figure 6 and 7 are hown the tep, 2, 3 and 4, a in Figure 3. Figure 5 introduce the equivalent proce of the tator and winding izing and Figure 6 introduce rotor and quirrelcage/end-ring izing. Figure 5 Step, 2, 3 e 4 Part Stator Sizing 6

7 Figure 6 Step, 2, 3 e 4 Part 2 Rotor Sizing The lat tep of the oftware (tep 5) i diplayed in Figure 7. In thi tep are carried out the performance calculation. Moreover, thee calculation are in agreement with the tandard utilized in thi work. The oftware ha a window uer interaction, howing deign information and et the required input to the project. Several creen were deigned for the variou tage of the project. Thi wa created in effort to make the oftware more uer friendly for new our infrequent uer. Thi paper will not diplay all the developed window, o that only the main window are preented. Figure 8 how the main input data window. All the window were developed in Portuguee language. The input data are: rated power, ynchronou rotation, upply frequency, upply voltage, phae number, ervice factor, lamination factor, and the target parameter are: power factor, efficiency, locked rotor torque, breakdown torque and locked rotor current. Figure 7 Step 5 Motor performance. 7

8 Figure 8 Main window Figure 9 how the tator reult window. Furthermore, it preent everal izing reult, like: tator lot, teeth, output diameter and internal tator diameter Figure 9 Stator reult window Figure 0 preent the rotor izing reult window. It how everal izing reult, like: lot rotor, haft diameter, internal rotor diameter and the bar/end ring izing. 8

9 Figure 0 Rotor reult window All computed motor deign data are tored in a preadheet and the performance tet reult a well. 5. Deign Thi ection aim to introduce CAD deign of an induction motor with.5 hp, 380 V, deign N (imilar to NEMA deign B), 4 pole, 60 Hz, unit ervice factor load, targeted efficiency 8.5%, targeted power factor 0.79,.9 pu locked rotor torque and 2 pu breakdown torque. The ferromagnetic core hould be made of teel-ilicon alloy (3.5%) with thickne of 0.5 mm. The tator winding ha 3 lot/pole/phae, full pitch coil, without current path in parallel, fill factor 40% and.5 apect ratio. According to [8] the motor mut have frame ize type 80. The flux denity in the air gap around hould be around 0.7 T, the tooth flux denity between.5 T and.65 T and the back core flux denity between.4 T and.7 T. Inulation cla i B, however it i a high-efficiency motor with a reference temperature of 80º C [7]. The bar kewing i equivalent to the rotor lot pitch length. The current denity in the tator winding i 4.5 A/mm² and current denity in the rotor bar i 3.4 A/mm². Analyzing only the tator winding, it can be een that motor deign ha the important propertie hown in Table. It can be verified that the performance tet were atifactory, but for the purpoe motor deign only the efficiency i introduced in Table. Increaing the number of path current to reduce area of the coil conductor (without modifying the lot area), i likely to increae the motor efficiency. The modified data in the deign are hown in Table 2. The new fill factor value i 0.56 and it i et the number of current path equal to 2. After the lot izing (keeping the lot area contant), the Table 2 how the reizing of the motor winding (increaing the path current in parallel), reulting in a better efficient. Thi ection decribe the oftware veratility to obtain the motor izing and ubequent adjutment were neceary to improve the deign requirement, epecially in the improved efficiency a hown in Table 2. 9

10 Table Winding deign reult Winding parameter W 276 n 46 N 46 b n cond d 0.9 mm cond a K 0.4 fill Calculated value A lot 73.2 mm² 83.3% Table 2 Modified winding deign reult Winding parameter W 552 n 92 N 92 b n cond d 0.75 mm cond a 2 K 0.56 fill Calculated value A lot 73.2 mm² 84.8% 6. Concluion The paper introduce that the contructive apect of the induction motor uing a CAD tool i intereting, fat and erve like an initial tep to improve the machine deign, conequently, the efficiency. The oftware doe not exclude other technique, which can refine de deign, e.g. finite element method, being it main advantage. It i highlighted that uch technique improve the efficiency without extra tooling cot i important after ue of oftware. Since jut the number of path current wa increaed, without changing the area of the tator lot, the increae on number of turn/phae reduce the conductor area, increaing the wire cot in the motor contruction. Since the price/km for econd calculated wire (ee table 2) i 20% le than the price/km of the firt calculated wire (0.9 mm diameter) and the firt calculated wire coil/phae length i 4 m (276 turn/phae), the cot of copper increae 60% becaue the coil length i 228 m (552 turn/phae). Furthermore, the oftware allow teting different motor technique, uch a: increae of the motor length, which hould alo increae the motor efficiency [5]. A future oftware upgrade will include the parameter of minimum torque a recommended in the Brazilian tandard [8]. The minimum torque i developed from the torque-peed curve of an induction motor. Another oftware improvement i to provide the oftware to downloading on a webite and an Englih-language verion. 0

11 Reference [] 0th Congre of the United State. Energy Independence and Security Act of 2007, January Can be downloaded at: [2] Commiion Regulation (EC) No 640/2009. Implementing Directive 2005/32/EC of the European Parliament and of the Council with regard to ecodeign requirement for electric motor. Official Journal of the European Union L 9, 23/07/2009 p Can be downloaded at: [3] República Federativa do Brail. Portaria Interminiterial nº 553/ Programa de meta de motore elétrico de indução trifáico, December Can be downloaded at: l_nx_553_2005.pdf [4] Boglietti A., Cavagnino A., Ferrari L., Lazzari M., Luparia G. No tooling cot proce for induction motor energy efficiency improvement. IEEE Tranaction on Indutry Application. May/June 2005, Vol. 4, no.3. [5] Agamloh, E., Boglietti, A., Cavagnino, A. The incremental deign efficiency improvement of commercially manufactured induction motor. Proc. of the ECCE 202 IEEE (Raleigh, USA, 5-20 September 202). ISBN Can be ordered from [6] Kocaba D. A. Novel Winding and Core Deign for Maximum Reduction of Harmonic Magnetomotive Force in AC Motor. IEEE Tranaction on Magnetic. February 2009, Vol. 45, no.2. [7] Boldea, I., Naar, S. A. The induction machine deign handbook, Ed.: CRC Pre (USA), 200. ISBN [8] Brazilian Standard. Rotating electrical machine Induction motor. Part : Polyphae, Ed.: ABNT (Brazil). ISBN [9] Brazilian Standard. Rotating electrical machine Dimenion and output erie for rotating electrical machine Standartization. Part : Aignment of frame between 56 to 400 and flange 55 to 080, Ed.: ABNT (Brazil). ISBN [0] Boglietti A., Cavagnino A., Lazzari M., Vachetto S. Preliminary induction motor electromagnetic izing baed on a geometrical approach. IET Electric Power Application Journal. November 202, Vol. 6, i. 9.