* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Effective Estimation of Induction Motor Field Efficiency Based on On-site Measurements
Immunity-aware programming wikipedia , lookup
Commutator (electric) wikipedia , lookup
Opto-isolator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
Three-phase electric power wikipedia , lookup
Alternating current wikipedia , lookup
Shockley–Queisser limit wikipedia , lookup
Buck converter wikipedia , lookup
Power engineering wikipedia , lookup
Induction cooking wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Dynamometer wikipedia , lookup
Voltage optimisation wikipedia , lookup
Electric machine wikipedia , lookup
Electrification wikipedia , lookup
Distribution management system wikipedia , lookup
Electric motor wikipedia , lookup
Brushless DC electric motor wikipedia , lookup
Brushed DC electric motor wikipedia , lookup
Stepper motor wikipedia , lookup
Effective Estimation of Induction Motor Field Efficiency Based on On-site Measurements T. Phumiphak* and C. Chat-uthai** * Electrical Power Engineering Department, Faculty of Engineering, Mahanakorn University of Technology, Bangkok 10530 Thailand ** Department of Electrical Engineering, Faculty of Engineering, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520 Thailand ABSTRACT This paper proposes the effective technique for estimating efficiency of existing three-phase induction motors in the field. This technique focuses on the operating efficiency of motors without the need for removing the motors and without the need for measuring the output power or torque. This paper describes the use of a few sets of data (voltage, current, power, speed) measured from the motor (on-site) coupled with the genetic algorithms for evaluating the motor parameters instead of using the no-load and blocked rotor test results. Once these parameters are known it is possible to obtain the estimated efficiency of the motor. To illustrate how well the estimated efficiency match that of the calculated obtained from the standard evaluations, the results of various induction motors rating 10 up to 100 hp are presented. Test results indicate that this proposed technique has a high accuracy, and then it could be suitable for conducting on-site energy audits of existing motors in order to support a decision to replace operating motors with a higher-efficiency model. Keywords: Field Efficiency, Genetic Algorithms, Threephase Induction Motors, On-site Energy Audits. 1. INTRODUCTION The majority of motors in the industry are induction motors. There may be various reasons for the desire of testing an existing induction motor in the field, such as consideration of exchanging out of date or worn motors with new, or checking the efficiency after rewinding. Particularly the output power of motor is hard to detect. One of established procedures is therefore to calculate the efficiency by measuring the losses and subtract them from the input to find the output. There are many methods pertinent to field efficiency evaluation in the literature and the new methods are appearing every year [1-5]. In the past, many methods were used to calculate the induction motor efficiency, one common method is to test the motor under load conditions and then monitor the input and output at different load points using a dynamometer and torque transducer (if possible). This is the most straightforward method to measure the output power directly from the shaft without any need to calculate losses. The shaft torque method offers the most accurate field efficiency evaluation method, however, it is not suitable for field evaluation because this process involves the removal of motor from service to place it on a test stand and couple it to the dynamometer. It can be seen that this method is impractical and costly. In the field, one may estimate the efficiency based on information from the nameplate and input measurements in which a few problems may occur. First, the nameplate efficiencies of a given motor can be evaluated according to different standards. Second, the nameplate data are rounded, the error in estimated efficiency can be very high. Third, the motor may have been rewound. Comparison of actual motor efficiencies is certainly a valid tool to justify the use of one motor over another. In order to conduct energy consumption of motors (on-site energy audits), the operating efficiency of these motors must be known. It is essential that the efficiency of motor should be estimated quickly with minimum disturbance to the service. The objective of this paper is to propose a new technique that can help the plants to make the right decision in replacing the inefficient motors with more efficient ones using the results of the effective estimation of induction motor field efficiency. 2. EFFECTIVE ESTIMATION OF INDUCTION MOTOR FIELD EFFICIENCY The calculation of the operating efficiency in this present work is based on the equivalent circuit method. The motor parameters can be estimated by using a few sets of data from the field test and nameplate information coupled with the genetic algorithms [6] instead of using the no-load and blocked-rotor test results which are undoubtedly a tedious and time consuming task if the motor is already coupled to driven equipment in the process. The field test data can be obtained from the measured values at any one operating point test (OPT) or two operating points test (TPT). Note that this technique is suited to general purpose when the motor cannot operate at no-load. This technique relies on measuring the input voltage, current, electrical power, stator resistance and output speed of the motor in the field test at any load. The proposed equivalent circuit parameters per phase of three-phase induction motor is shown in Fig. 1. This model can be represented the steady state behavior of an induction motor where R1 jX1 jX2 Rc jXm I1 V1 Ztotal parameters proceeds as follows: Input the nameplate information and measure the stator resistance. Then from the field test of motor (on-site) directly measure one operating point or two operating points of motor input voltage, current, power and output speed which need not be close to no-load or full-load values while the motor is in service. Select the method of OPT or TPT. As a result, it is possible to estimate the motor efficiency in the field in a short time. RSLL R2 s Fig.1: Proposed Equivalent Circuit of Induction Motor R1 : stator resistance, General Data : Rated Output Power (kW) Rated Voltage (V) Rated Current (A) Rate Speed (rpm) Measure Stator Resistance X 1 : stator leakage reactance, Rc : core loss resistance, X m : magnetizing reactance, R2 : rotor resistance referred to stator, X 2 : rotor leakage reactance referred to stator, s : slip OPT TPT Select Method Most models used in the past eliminated the stray load loss. Neglecting this loss introduces a significant error in estimating the efficiency. The stray load loss will decrease with decreasing output power proportional to the square of the torque [7]. It is worth mentioning that this proposed model includes the stray load loss parameter RSLL . The parameter RSLL can be expressed as RSLL = m (1 − s f ) R2 (1) sf where m denotes the per unit of the full-load power which is set to be the variable ( 0.002 < m < 0.018 ) [7] and s f is the full-load slip. From the equivalent circuit, Point 1 : - Input Voltage (V) - Input Power (W) - Input Current (A) - Speed (rpm) Point 1 : - Input Voltage (V) - Input Power (W) - Input Current (A) - Speed (rpm) Point 2 : - Input Voltage (V) - Input Power (W) - Input Current (A) - Speed (rpm) Process : Motor Parameters Evaluation Using Genetic Algorithms Process : Motor Parameters Evaluation Using Genetic Algorithms Output : Performances of Motor at Point 1 Load Output : Performances of Motor at Any Load the equations of stator phase current I1 and total input power Pinput can be expressed as V1 I1 = , Ztotal 3. EXPERIMENTAL RESULTS AND DISCUSSION Pinput = 3 V1 I1 ( PF ) (2) where V1 and I1 are rms values of the input phase voltage and current respectively, and PF is power factor. The equivalent circuit parameters can be estimated by using the data from field test coupled with genetic algorithms. The aim of genetic algorithms is to minimize the error of (3), or to maximize the fitness of (4). n Fobjective = ∑ I1i ,cal i =1 I1i , mea Fitness = 2 n −1 + ∑ Pinput i ,cal i =1 Pinput i , mea 100 100 + Fobjective Fig.2: Flow Chart of Proposed Technique The proposed technique described in the preceding section is applied to three different size three-phase induction motors as shown in Table 1. These motors were tested using standard performance evaluations, i.e. IEEE Std 112 Method B [7] (for 100, 15, 10 hp) and IEC 34-2 [8] (for 100 hp). The motor efficiencies were calculated using the analysis procedure described in those standard performance evaluations. Table 1: Nameplate Information of Motors 2 −1 (3) (4) Hz V A r/min Pole 100 hp [9] (75 kW) 50 400/690 131/76 1488 4 15 hp [10] (11.2 kW) 50 380 21.6 1450 4 10 hp [10] (7.5 kW) 50 380 15.2 1445 4 where I1i ,cal and Pinput i ,cal are the calculated values using (2). I1i ,mea and Pinput i ,mea are the measured values obtained from the field test when n = 1 for the OPT and n = 2 for the TPT methods. The flow chart of the proposed technique is shown in Fig. 2. The technique for estimating the equivalent circuit Table 2 shows the field test data of 100 hp motor at various loads (25, 50, 75, 100%). The measured data in Table 2 can be used to estimate the motor parameters and to calculate the motor efficiency which can select the method of using the OPT or TPT. The data of the OPT (one operating point) can be at any 25% or 50% or 75% Measured Input Voltage (V) Input Current (A) Input Power (kW) Speed (r/min) 25% 400 56.8 20.51 1497.5 Motor Load 50% 75% 400 400 77.8 103.8 39.68 59.07 1495 1492 100% 400 132.5 78.53 1489 The results of estimated efficiency of the 100 hp motor using the proposed technique are summarized in Table 3 and Fig. 3. At one-quarter load, the measured efficiencies obtained from IEEE 112 Method B and IEC 34-2 are 93.2 % and 92.9 % respectively, while the estimated efficiency obtained from the TPT is 91.4 % and the OPT is 91.9 %. At full-load, the measured efficiencies are 95.8%, while the estimated efficiencies are 95.2 % and 95.9 %. It can be observed that the accuracy of estimation is higher at full-load than at one-quarter load. Note that from Table 2 (100 hp), the synchronous speed is 1500 r/min while the speed at one-quarter load is 1497.5 r/min and at full-load is 1489 r/min. This can be attributed to the fact that at lower load the slip becomes smaller. Therefore, any small error in measuring speed will result in a significant error in slip. 88 2/4 95.4 94.6 94.6 94.5 94.6 94.5 95.5 95.5 94.3 - 1/4 4/4 95.6 95.2 95.2 95.1 95.2 95.2 95.8 95.8 95.9 95 Efficiency 5/4 95 94.7 94.7 94.6 94.7 94.7 95.5 95.4 25&50 25&75 25&100 89 50&75 50&100 75&100 IEEE112 87 IEC34-2 93 91 85 2/4 3/4 4/4 2/4 3/4 4/4 5/4 6/4 Motor Load Fig. 4: Estimated Efficiency Using TPT and Standard Evaluations Versus Load for 15 hp Motor 25&50 25&75 25&100 90 88 86 84 82 80 78 76 74 50&75 50&100 75&100 IEEE112 1/4 2/4 3/4 4/4 5/4 6/4 Motor Load 97 1/4 82 76 5/4 Motor Load Fig. 3: Estimated Efficiency Using TPT and Standard Evaluations Versus Load for 100 hp Motor Fig. 5: Estimated Efficiency Using TPT and Standard Evaluations Versus Load for 10 hp Motor OPT 95 IEEE112 IEC34-2 90 Efficiency 1/4 93.0 91.4 91.4 91.4 91.4 91.4 93.2 92.9 91.9 - 50&75 50&100 75&100 IEEE112 84 78 85 80 75 70 10 hp 15 hp 100 hp Fig. 6: Estimated Efficiency Using OPT at 25 % load and Standard Evaluations Versus Various Motors at 1/4 load OPT 98 96 94 Efficiency Method 25%&50% 25%&75% 25%&100% 50%&75% 50%&100% 75%&100% IEEE 112 B IEC 34-2 25% 50% 75% 100% 86 80 Table 3: Summary Results of Estimated Efficiency for 100 hp Motor at Various Loads Using TPT and OPT Motor Load 3/4 95.8 95.3 95.3 95.2 95.3 95.3 95.9 95.9 96.2 - 25&50 25&75 25&100 90 Efficiency Table 2: Field Test Data of 100 hp Induction Motor The estimated efficiencies using the TPT at various loads of the 15 and 10 hp motors can be illustrated in Figs. 4 and 5 respectively. For the OPT, the estimated efficiencies of various motors at 1/4, 2/4, 3/4 and 4/4 load can also be illustrated in Figs. 6 to 9 respectively. Efficiency or 100%. The data of the TPT (two operating points) can be at any 25 and 50%, or 25 and 75%, or 25 and 100%, or 50 and 75%, or 50 and 100%, or 75 and 100%. IEEE112 IEC34-2 92 90 88 86 84 82 80 10 hp 15 hp 100 hp Fig. 7: Estimated Efficiency Using OPT at 50 % load and Standard Evaluations Versus Various Motors at 2/4 load OPT 98 IEEE112 96 IEC34-2 Efficiency 94 92 90 88 86 84 82 10 hp 15 hp 100 hp Fig. 8: Estimated Efficiency Using OPT at 75 % load and Standard Evaluations Versus Various Motors at 3/4 load OPT IEEE112 IEC34-2 98 96 Efficiency 94 92 90 88 86 84 82 10 hp 15 hp 100 hp Fig. 9: Estimated Efficiency Using OPT at 100 % load and Standard Evaluations Versus Various Motors at 4/4 load Figs. 3 to 9 show that the agreement between the estimated and measured efficiencies of the actual motors is good (error less than 2%). As mentioned in Section 2, the stray load loss was not ignored in this analysis; as a result the accurate value of motor efficiency can be obtained. The effect of neglecting the stray load loss can lead to dramatic error in the estimation. It is clear that the motor replacement decisions can not be made using such large errors in estimation since these errors can wipe out the potential savings, thus leading to a wrong decision. Considering the results obtained, it can be stated with confidence that this simple fast and low-cost technique will yield virtually the same results as using the sophisticated standard tests. 4. CONCLUSION The proposed technique for estimating efficiency of induction motor in the field has been described. This technique relies on the on-site measurement of the input voltage, current, power and actual motor shaft speed without conducting no-load and blocked-rotor tests. The measured data need not be close to no-load or full-load values and can be only one or two operating points. These data are used for estimating the parameters of equivalent circuit which includes the proposed stray load loss parameter for improving the accuracy. The estimated efficiency is then determined by using these parameters. Note that the OPT can accurately estimate the efficiency only at that test point while the TPT can accurately estimate at any motor load. The important advantages of this proposed technique over other methods are that it is a simple procedure, therefore it is possible to estimate the efficiency of motor in a short time while the motor is in service (its shaft is permanently connected to its load) without the removal of motor from service and that such procedure is inexpensive. The results indicate that the acceptable estimated efficiencies compared to those achieved from standard tests are obtainable (error less than 2 %). However, it is recommended when using this technique that the input frequency and revolutions per minute must be measured as accurately as possible. It is worth noting that this proposed technique is suitable for conducting on-site energy audits of actual motors which are then used to project a cost savings and payback. This information can then be used to guide the decisions regarding the investment in higher efficiency motors. 5. REFERENCES [1] J. S. Hsu, and B. P. Scoggins, “Field Test of Motor Efficiency and Load Changes Through Air-gap Torque,” IEEE Trans. Energy Conv., vol. 10, no. 3, pp. 471-477, Sept. 1995. [2] J. S. Hsu, J. D. Kueck, M. Olszewski, D. A. Casada, P. J. Otaduy, and L. M. Tolbert, "Comparison of Induction Motor Field Efficiency Evaluation Methods," IEEE Transactions on Industry Appli., vol. 34, issue:1, pp. 117-125, Jan./Feb. 1998. [3] F. Alonge, F D’Ippolito, G. Ferrante and F.M. Raimondi, “Parameter Identification of Induction Motor Model Using Genetic Algorithms,” IEE Proc.,Control Theory Appl., vol. 145, no. 6, pp. 587593, Nov. 1998. [4] A. Gastli, “Identification of Induction Motor Equivalent Circuit Parameters Using the Singlephase Test,” IEEE Transactions on Energy Conv., vol. 14, no. 1, pp. 51-56, March 1999. [5] K. S. Huang, Q. H. Wu, and D. R. Turner, “Effective Identification of Induction Motor Parameters Based on Fewer Measurements,” IEEE Trans. Energy Conv., vol. 17, no. 1, pp. 55-60, March 2002. [6] T. Phumiphak and C. Chat-uthai, “Estimation of Induction Motor Parameters Based on Field Test Coupled with Genetic Algorithm,” Proceedings of 2002 International Conference on Power System Technology, PowerCon 2002, vol. 2, Kunming, China, pp. 1199–1203, Oct. 2002. [7] IEEE Standard Test Procedure for Polyphase Induction Motor and Generators, IEEE Standard 112-1996, New York, May 1997. [8] Methods for Determining Losses and Efficiency of Rotating Electrical Machinery from Tests (Excluding Machines for Traction Vehicles), IEC 34-2, 1972. [9] Technology Procurement Project IEA Hi-Motor Competition, Jury Report, International Energy Agency, Demand Side Management, Dec. 1998. [10] Motor Efficiency Test : According to IEEE Std 1121996 (Method B), Test Report, Metropolitan Electricity Authority (MEA), Thailand, March 2002.