562 IEEE TRANSACTIONS ONINDUSTRIAL ELECTRONICS, VOL. 55, NO. 2, FEBRUARY 2008 Performance Analysis of Centrifugal Pumps Subjected to Voltage Variation and Unbalance P. Giridhar Kini, Ramesh C. Bansal, Senior Member, IEEE, and R. S. Aithal Abstract—Frequent variation of single-phase loads on power system networks results in voltage ﬂuctuations and imbalance at consumer terminals. The application of such ﬂuctuating voltages to operate centrifugal loads causes large variations in system performance. As a consequence, the incorporation of large safety factors have resulted in efﬁciency of pumping operations being less than 50% in most cases. However, small improvements in pump efﬁciency can lead to a signiﬁcant reduction in energy consumption, and at the same time energy usage can be optimized. The operating point of a pump is obtained when the system curve intersects the pump curve. Variation in applied voltages leads to variation in the operating point, leading to inefﬁciency of system operation. This paper presents the impact of voltage varia- tion and imbalance on the working performance of an induction motor-driven centrifugal pump system with an experimental study. Both overvoltage and undervoltage conditions along with phase imbalance were considered for analysis. Index Terms—Centrifugal pump, discharge, head, induc- tion motor, International Electrotechnical Commission (IEC), operating point, pump curve, system curve, system efﬁciency volt- age unbalance. I. I NTRODUCTION T HE INDUSTRIAL sector is the largest consumer of all electrical power generated. Of the total energy available, over 60% is being utilized by motor drives, and in partic- ular, by three-phase induction motor-driven systems [1]. In general, most consumption of electrical energy among motor- driven systems are for pumping applications. Pump systems are predominantly used in the domestic, commercial, agricultural and industrial contexts for water pumping, municipal utilities for wastewater transport and a large number of specialized industrial sectors for ﬂuid transportation. Among the various types available, centrifugal pumps are widely used for their versatility in the ﬁeld of pumping liquids. Since electrical energy is an important resource for all industrial processes, the industrial sector now allocates money and effort on ensuring quality and reliability of the power supply at all times. Energy conservation and management, which are integral parts of industrial development, can be achieved by proper operation and maintenance of various subprocesses of a plant process [2], [3]. The major gains of effective energy management can Manuscript received March 30, 2006; revised October 1, 2007. P. G. Kini and R. S. Aithal are with the Department of Electrical and Electronics Engineering, Manipal Institute of Technology, Manipal University, Manipal, 576 104, Karnataka State, India (e-mail: giridhar.kini@manipal.edu). R. C. Bansal is with the Electrical and Electronics Engineering Department, School of Engineering and Physics, The University of the South Paciﬁc, Suva, Fiji (e-mail: rcbansal@hotmail.com). Digital Object Identiﬁer 10.1109/TIE.2007.911947 be fully realized through appropriate policies and practices at an individual unit level rather than at a collective plant level. However, estimation of energy saving potential in any industrial environment is a signiﬁcantly difﬁcult task, as it depends not only on the application involved, but also on the operating conditions [4]. In the case of motor-driven loads, slight changes in the operating condition signiﬁcantly vary induction motor parameters [5]. This paper presents an analysis of the effects of voltage variation and imbalance on the performance of a centrifugal pump system with an experimental case study. II. REASONS FOR I NEFFICIENCY AND I NACCURACY System performance is dependent on motor and pump per- formance. For the purpose of analysis, the motor-driven pump system is separated into two units: motor and pump. The factors which inﬂuence motor performance include the supply system parameters, motor loading, motor surroundings, and maintenance schedules, while factors responsible for pump performance include its ﬂow rate, head, and efﬁciency. A. Voltage Variation and Imbalance There are a number of events that can be categorized under “power quality degradation phenomena,” occurring during the day-to-day operation of a power system. The most frequently occurring are voltage variation and imbalance. This is quite common particularly in rural or weak power systems. The prob- lem is more severe if the utility happens to be the last load point in the feeder network. At the same time, the presence of a large number of nonlinear loads across the power system network degrades the power quality in a distribution system [6], [7]. A change in the three-phase voltage magnitudes has a large effect on motor performance [8], [9]. Frequent variation, in addition to unequal distribution of single-phase loads within the utility premises normally leads to imbalance of three-phase voltages. Induction motors are used as drives for a variety of applications and are always designed to tolerate a small level of imbalance. A small percentage of voltage variation and imbalance always exists in the power system network and therefore has to be managed. The causes of voltage imbalance and performance analysis of induction motors are well-documented [3], [8]–[18]. Use of energy-saving systems such variable speed drives across the power system network have increased the problem of voltage variation and imbalance [19], [20]. The occurrence of ﬂuctuations and imbalance among the three phase voltages are also not solely in control of the utility. Since the level of 0278-0046/$25.00 © 2008 IEEE