NON-STATIONARY HEATING OF LOW-POWER INDUCTION MOTOR UNDER CONTINUED OVERLOAD

Transcription

1 ENGINEERING FOR RURL DEVELOPMENT Jelgava NON-STTIONRY HETING OF LOW-POWER INDUCTION MOTOR UNDER CONTINUED OVERLOD ndri Snider lexey Gedzur Latvia Univerity of griulture btrat. The paper diue tranient heating proee and the repone of a low-power indution motor to permanent ontant load overload and a loked rotor under a tandard eletrial upply ytem (38V 5 Hz) for old initial ondition and ontant ambient temperature. The experimental invetigation are performed on a 1.1 kw totally enloed fan-ooled three-phae indution motor. The tranient temperature are meaured in 6 point of the tator end winding and in point of the motor aing uing thermoouple urrent enor and logger for data proeing and arhiving. The reitive tator loe for ingle-phae are alulated uing the tator winding equivalent parameter onidering the dynami hange of the tator urrent and the winding reitane from temperature. The experimental tet and analytial alulation how that the tator winding heating urve obey the firt order non-tationary thermal proe with time dependent thermal apaity and heat diipation fator a the funtion of the motor part temperature. nalye of the tudy reult how that an adaptive elf-tuning virtual model of the indution motor thermal proe hould be ompoed for adequate programming of the proeor-baed motor protetive devie to improve their operation quality. Key word: indution motor urrent loe heating temperature ontinued overload thermal model. Introdution Low voltage indution motor (4 V 5 Hz) have got large appliation in indutry and agriulture onuming the majority of the total eletrial energy onumption in the world. They are available in a wide hoie a from everal ten watt up to everal hundred kilowatt. Typial indution motor (IM) appliation in rural indutry inlude pump fa ompreor mill aw mahine rane onveyor ruher et. The tatiti have hown that depite the IM high reliability and impliity of ontrutio the annual motor failure rate i onervatively etimated at 3-5 % per year and in extreme ae up to 1 % [1]. IM failure aue eential diret and tehnologial loe involving the motor replaement and repair a well a interruption of the prodution proe. IM failure may be laified a follow: 1) eletrial related failure ~35 %; ) mehanial related failure ~31 %; 3) environmental impat and other reaon related failure ~34 % [1]. nalye of the IM failure reaon how that many of them are aued by prolonged heating of the different part involved in IM operation. That i why an aurate traking of the IM thermal tatu and adequate repone of the protetion ytem to thermal overload i very important. Modern trend in eletri motor ontrution are to make IM more ompat and effiient. t the ame time the new IM are more enitive to mehanial and eletrial overload. On the other hand overetimation of the thermal tate of the indution motor an aue undeirable IM toppage and uele interruption of the prodution proe. Therefore it i very important to predit the thermal ondition of the indution motor and to develop a deirable aurate and flexible thermal model of IM operation under prolonged overload. detailed deription of experimental and analytial reearh method and reult of the tranient heating of IM part and thermal modelling i given in []. If the thermal model i ued in the IM deign proe a fairly omplex model i neeary baed on the numerial finite element method. If the thermal model i ued for determining the heating of the exiting IM part a impler model an be ued often referred to a the thermal network model []. The mot enitive part of IM to thermal overload i tator winding. The main limiting fator of IM ontinuouly loading i the tator winding temperature. Exeeding the temperature limit reult in aeleration of the oxidation proe in the inulation material what eventually lead to IM damage. Commonly for the heating proe of the IM tator winding the firt-order thermal model with ontant parameter [3] or two level variable parameter different for initial and for final period have been ued [1]. For intane the thermal and eletrial parameter of IM vary ontinuouly during all heating tranient proe. ppliation of oft tarter and frequeny onverter inreae the loe due to higher harmoni and aue more intenive heating of the IM tator winding and other part [4; 5]. 536

2 ENGINEERING FOR RURL DEVELOPMENT Jelgava The main tak of thi work are to get experimental harateriti and thermal parameter of the IM tator winding heating proe for old initial ondition and prolonged rated load overload and loked rotor. Reearh objet and method The thermal reearh objet i a three phae indution motor: 4X84Y3; /38 V; 4.9/.8 ; IP44; in.l. [B] m = 14.5 kg; P = 1.1 kw; n = 14 min -1 ; =.67; η =.75; oφ =.81. The tator iruit parameter: reitane R a = 7.9 Ω and impedane Z = 17.3 Ω at ambient temperature a = 4 ºC are obtained by meauring. Reatane i alulated from X = (Z R a ) -.5 = 15.4 Ω. diret urrent generator (P-Y4 V 5.9 P = 1 kw n = 15 min -1 ) and a lamp rheotat for IM loading i ued. The blok diagram of the tet benh et-up for onduting the experimental tet i hown in Figure 1. The tet benh i fitted with adequate laboratory meauring equipment voltmeter (V) ammeter () and watt meter (W) for monitoring of three phae urrent voltage and power. For preie meauring of IM tator aing (frame) and winding temperature eight miniature thermoouple BK-5 (air probe SE) are intalled. ll thermoouple are onneted to a data logger TC-8 with built in old juntion ompenation (PICOLOG oftware Window driver auray of temperature reading - ±.5 ºC). The tator aing urfae temperature are meaured in two point by thermoouple T 4 and T 5. They are mounted at the aing haft ide and fan ide (Fig. 1). The tator winding temperature are meaured for eah phae ( B C) by ix thermoouple attahed to the end winding. Three thermoouple (T 1 T T 3 ) are plaed at the haft (drive) ide and the other three (T 6 T 7 T 8 ) at the fan ide. To get a good thermal ontat the thermoouple are inerted into natural gap in the end winding and bonded by thermal bandage. For preie meauring of IM tator urrent during all tranient heating proe the urrent enor urrent lamp 3XT11C and the data logger EL5 (auray ± 1 %) are intalled. B C N V U V U B V U C I I1 I B I C3 W W P 1 P PP in =P 1 ±P in = P 1 + P 1 S 3 S S 1 Current logger Diret urrent generator Shaft T 3 T T 4 T 5 T 6 T 7 Fan T 1 T 8 W P out Lamp Temperature logger rheotat Dator PC Fig. 1. Tet benh et-up for indution motor heating experimental reearh: T 1 T T 3 thermoouple (end winding haft ide); T 4 T 5 thermoouple (aing haft ide fan ide); T 6 T 7 T 8 thermoouple (end winding fan ide); S 1 S S 3 urrent enor 537

3 ENGINEERING FOR RURL DEVELOPMENT Jelgava ll heating tet are made for old initial ondition initial temperature of IM all part i equal to ambient temperature ( = a ). Supply voltage and frequeny are traditional and uniform with the rated value (38 V 5 Hz) in all phae. The winding and aing temperature tranient rie tet erie are run for three mode of IM operation: 1) rated load; ) overload; 3) loked rotor (tandtill). IM load i determined by a oeffiient in relation to the tator urrent k i = I /I r where I atual tator urrent ; I r rated tator urrent. The reult of IM heating experimental reearh are hown in Figure Reult and diuion 1. IM heating repone to permanent mehanial load under old initial ondition Figure how the IM thermal repone to permanent rated load. The initial temperature of IM all part equal to ambient temperature = a = 6 ºC. The loading generator i harged to the lamp rheotat aording to the IM approximate rated urrent I =.67. The tator winding temperature rie aue the tator urrent redution from the beginning value.67 at 6 ºC to the end value.5 at 85 ºC beaue of winding reitane growth. Relative tator urrent k i = I /I r =.67/.8 =.95. The haft ide end winding teady-tate temperature i up to 6 ºC higher than the fan-ide temperature beaue of the different heat diipation value H (W ºC -1 ). The fan ide ooling ondition are better therefore the H value i higher and the end winding temperature i lower. The frame heating harateriti demontrate an eential role of ventilation on the ooling effiieny. The fan ide teady-tate temperature f = 37 ºC i 4 % lower than the haft ide one = 5 ºC. 9 ºC 8 y = -6E-8x 6 + 1E-5x x x x x R =.9987 =f(t).9 I.8 7 f=f(t) y = -6E-8x 6 +1E-5x x x x x R = y =. x x x R =.9989 =f(t) I=f(t) y = 3E-5x -.43 x R = f = f ( t) y = 8E-5x x x R = = a f(t).3 τ 1 = 7min τ = 15min y =.7 x R = t min 6. Fig.. Repone of indution motor part temperature to permanent rated load for old initial ondition: (t) temperature of tator end winding haft ide ºC; f temperature of tator end winding fan ide ºC; (t) temperature of aing haft ide ºC; f (t) temperature of aing fan ide ºC; a (t) ambient temperature ºC; I (t) tator urrent ; τ 1 τ thermal time ontant Figure 3 how the IM thermal repone to permanent overload by the tator urrent: k i = I /I r = = 3.18/.8 = 1.14 (14 %). The initial temperature of IM all part i equal to ambient temperature 4 ºC. The loading generator i harged aording to the IM overload initial urrent 538

4 ENGINEERING FOR RURL DEVELOPMENT Jelgava I = The tator winding temperature rie aue the tator winding reitane growth and urrent redution from the beginning value 3.18 at 4 ºC to the end value.95 at 11 ºC. Under overload the ventilation effet on temperature differene at the haft ide and fan ide i greater. The end winding haft ide teady-tate temperature i up to 1 ºC higher than the fan-ide temperature but the differene of the aing urfae temperature i up to 5 %. Under higher overload the role of ventilation on the ooling effiieny of the IM winding and aing inreae. It i a problem for the high lip indution motor. Interpolation of the IM heating tet tetify that the tator winding thermal model i non-tationary with temperature dependent parameter. Even the 6 th order polynomial regreion diatifie the needed dynami auray. 1 ºC 11 y =-5E-7x 6 +7E-5x x x x x R =.9998 =f(t) 3.3 I y = 4E-7x 4-3E-5x x x R =.97 I =f(t) =f(t) f = f ( t) y =-6E-7x 6 +7E-5x x x x x R =.9995 y =.5 x x x R = τ 1= 7min τ = min a =f(t) f=f( t) y =.44 x R =.997 y = -.51 x x R = t 35 min 4 Fig. 3. Repone of indution motor part temperature to permanent overload for old initial ondition: (t) temperature of tator end winding haft ide ºC; f temperature of tator end winding fan ide ºC; (t) temperature of aing haft ide ºC; f (t) temperature of aing fan ide ºC; a (t) ambient temperature ºC; I (t) tator urrent ; τ 1 τ thermal time ontant The ooling effiieny of the IM tator winding depend on the heat diipation fator H w. If the power loe P w and the orreponding teady tate temperature of the tator winding i determined by the experiment the heat diipation fator an been alulated: I R ( α + ) H w = (1) ( ) ( α + ) where I tator urrent at given tator winding temperature ; teady-tate temperature of tator winding ºC; = a initial temperature of tator winding equal to ambient temperature a ºC; R reitane of tator winding at ambient temperature Ω. α = ºC -1 reitane-temperature oeffiient of the ooper. Calulation aording to expreion (1) how that at rated load teady-tate H W = 1.4 W ºC -1 but at overload 14 % it i higher 1.7 W ºC -1 beaue of higher final temperature. If the load torque exeed the ritial torque the IM rotor tay at a tandtill mode. Loe in the tator winding are maximal P w = max the rotation peed n = the fan i out of order and heat 539

5 ENGINEERING FOR RURL DEVELOPMENT Jelgava diipation from the winding area H w = min. The heating proe i adiabati and after tranient time aued by thermoouple reation delay temperature rie gradually with ontant ramp v = 5 ºC -1 (Fig. 4). Temperature meauring teady tate error = v τ = m = 1 ºC where τ = thermoouple thermal time ontant ; atual temperature ºC; m meaured temperature ºC. The aing temperature tay ontant all period of the winding temperature rie from ambient temperature to the limit one 13 ºC (inulation la B). That tetifie an adiabati harater of the tator winding heating proe under the rotor tandtill mode. In thi ae the tator winding thermal model hould be highly preie to provide the tripping of the protetion devie with appropriate auray. On the bai of the tet reult (Fig. 4) the tator winding tranient temperature (t) at loked rotor an be expreed by a imple mathematial model: I R t ( t ) = + () H τ where I = 1.5 average tator urrent at long-term loked rotor; R = 9. Ω average tator winding reitane at long-term loked rotor; H =.54 W ºC -1 average tator winding heat diipation fator; τ = 15.1 min average tator winding thermal ontant at long-term loked rotor. 13 Θ 1 º C y = 5E-5x 4-46x x x R = 9991 Θ (t) Θ Θ m m (t) Θ (t) y = 7x R = t Fig. 4. Repone of indution motor part temperature to loked rotor mode for old initial ondition: (t) atual temperature of tator end winding haft ide ºC; m meaured temperature of tator end winding haft ide ºC; (t) temperature of aing haft ide ºC; meaurement teady-tate error of loked motor tator winding temperature ºC. Thermal model of IM tator winding The teady-tate performane of the IM tator winding heating temperature under load and overload an be deribed by the following equation: ( R = + K ) P = + K ( ) I (3) where K( ) variable enitivity fator a a funtion of rotation peed and temperature ºC W -1 ; P ingle-phae initial power loe at ambient temperature W; I initial tator urrent at ambient temperature. The meaured ingle-phae reitane of the tator winding i R = (7.9 ±.5) Ω if a = ( ± ) ºC. The variable enitivity fator K( ) hange during all tranient heating proe in aordane with the expreion: 54

6 ENGINEERING FOR RURL DEVELOPMENT Jelgava (1+ k K( ) = (1+ k k ρ ρ R α + [1+ ( ) ] ) k X α + = ) H( ) R α + [1+ ( ) ( ) ] H ( ) X α + where k ρ = ( ) =.6 quare of the relation of initial reitane to reatane; k reitane relative hange in order of temperature; H( ) heat diipation fator a a funtion of rotation peed and temperature W ºC -1 ; n IM rotation peed under variable load (rated value 14 min -1 ); X = 15.4 Ω ingle-phae tator winding reatane. The heat diipation fator hange ubtantially from the rotation peed and the temperature: H ( ) = [ h + h( )] S (5) where h heat tranfer oeffiient at n = and = = a W (m ºC) -1 ; h( ) heat tranfer oeffiient rie a a funtion of n and temperature W (m ºC) -1 ; n IM rotation peed under variable load (rated value 14 min -1 ); S diipation heat urfae area m. ording to the invetigation of Gunnar Kylander [] h = 6.5 W (m ºC) -1 h = 5.5 u r.6 at indefinite temperature where u r rotor peripheral peed m -1. The previou modeling of eletrial thermal unit [6] and analye of heating harateriti (Fig. 4) allow making a onluion that the model of the heat diipation fator for the tator winding an been earhed in the following form: n r a H ( ) = h + en ( ) + e [( a ) + b ( a )] S (6) 9.55 where e n e a b empirial oeffiient obtained from the heating tet; r IM rotor peripheral radiu m. The tator winding thermal time ontant depend on the thermal apaity C (J ºC -1 ) of the IM part involved in heat diipation from the winding and on the heat diipation fator H (W ºC -1 ): C[ ( t) ] τ w = (7) H[ t ] The graphial analye uing the tangent method how that the tator winding thermal time ontant τ w hange all over the tranient heating proe (Fig. 1 Fig. ). Initially it ha minimal value (τ w = τ 1 ) beaue of minimal ma involved in the heat tranfer proe (C = min) and a higher enitivity fator K (4) aued by a lower heat diipation fator (H = min). ll i vie vera at the end of the temperature rie the final time ontant i ubtantially higher than the initial one (τ» τ 1 ). Therefore aording to the tator winding heating proe an indution motor i a non-tationary objet with time dependent fator of thermal delay and heating enitivity. Conluion 1. The mot enitive part of the indution motor to thermal overload i the tator winding. The hoie of the IM ize and modifiatio a well a the hoie etup and programming of the motor protetion devie largely depend on the tator winding heating dynami what in it turn i determined by the motor parameter motor mehanial load and environment ondition.. Invetigation of the indution motor (4X84Y3: /38 V 4.9/ kw 14 min -1 ) tranient heating how that the initial ramp of the tator winding temperature rie i ubtantially higher beaue of minimal thermal time ontant (τ 1 7 min) in omparion with that at the end of the proe (τ 15 min) when temperature beome teady. ( ). (4) 541

7 ENGINEERING FOR RURL DEVELOPMENT Jelgava ording to the tator winding heating proe an indution motor i a non-tationary thermal objet with a time dependent ontinuouly inreaing thermal delay fator and falling enitivity fator during all the tranient proe of temperature rie. Referene 1. Venkataraman B. Godey B. Premerlani W. Shulman E.et. Fundamental of a Motor Thermal Model and it ppliation in Motor Protetion. In: Proeeding of 58 th nnual Conferene Protetive Relay Engineer Blak & Veath Corporatio Kana City US 5 pp Kylander G. Thermal Modelling of Small Cage Indution Motor: Tehnial Report No. 65 Goteborg Swede Chalmer Univerity of Tehnology p. 3. Zoholl S.E. Benmouyal G. Uing Thermal Limit Curve to Define Thermal Model of Indution Motor. Shweitzer Engineering Laboratorie Pennylvania (US) Quebe (Canada) Printed in US p. 4. Mukhopadhyay S.C. Predition of Thermal Condition of Cage-Rotor Indution Motor under Non Standard Supply Sytem. International Journal on Smart Sening and Intelligent Sytem Vol. No. 3 9 pp Solveon M. G. Mirafzal B. Demerdah N.. O. Soft-Started Indution Motor Modeling and Heating Iue for Different Starting Profile Uing a Flux Linkage BC Frame of Referene. IEEE Tranation on Indutry ppliatio Vol. 4 No. 4 6 pp Snider.. daptive Self-Tuning up Model for Non-Stationary Proe Simulation. In: Proeeding of the 9 th International Sientifi Conferene Engineering for Rural Development. Jelgava: LU 1 pp