# Energy Efficiency Analysis of Fixed-Speed Pump Drives with Various Types of Motors
## 1 Introduction  
Despite the high efficiency and the high dynamic and static performance of variable speed drives (VSDs), electric motors powered directly from the mains are widely used in many applications due to the high cost of frequency converters. For instance, the market share of variable-speed drives is estimated to be about 30% in Germany according to the European Commission data [1] and about 20% in Switzerland according to the study disclosed in [PERSON] and Tieben [2]. In particular, such widely used machines, including centrifugal pumps, compressors, and fans, do not require a wide adjustment range, high starting torque, or high speed. Therefore, induction motors (IMs) powered directly from the mains are widely used in the drives of the above-mentioned fluid machinery. Furthermore, several manufacturers offer line-start permanent-magnet synchronousmotors (LSPMSM) of a high energy efficiency class powered directly from the mains. The adjustment of fluid flow in this case is carried out using throttle control valves. According to the data from the International Energy Agency [3], electric motors consume 46% of the world's electricity. They account for about 70% of the total industrial electricity consumption. According to the report of the European Commission [3], pump systems consume almost 22% of all electric energy generated throughout the world, as shown in Figure 1. Therefore, it is a pressing task to study the possibilities of increasing the energy efficiency of pump units. Improvements in energy efficiency of a pump unit can be provided by implementing changes in the hydraulic network in which the unit operates by using control systems, including a variable-speed drive, by optimizing and distributing the load (when units run in parallel), as well as by proper selection of the unit parts, in particular, via the use of electric motors of a higher energy efficiency class [4]. The latter method is considered in [PERSON] et al. [4] as the most relevant method for pumps under throttle control. The minimum energy efficiency level for electric motors is defined in Annex I of European Commission [5]. Energy efficiency classes of line operated AC motors are determined in IEC 60034-30-1 standard [6]. In accordance with the EC regulation [5], since 1 January 2017, all electric motors with power ranging from 0.75 to 375 kW must have an energy efficiency class of at least IE3, or IE2 if they are used as part of a VSD (E4, IE3 and IE2 are labels of energy efficiency classes of electric motors according to IEC 60034-30-1 standard). Within the planned timeframe, according to Policy Option 4 [7], the introduction of the minimum acceptable energy efficiency class of at least IE4 is expected before 2030. The classification of electric motors in References [5,6] takes into account only the motor rated efficiency specified by the rated shaft power, but not the motor efficiency at underload modes, which is of at least comparable relevance for motors used as components of pump units [8]. In practice, most of the time, the centrifugal pump is employed at low or medium loads. However, the pumps are designed and integrated to satisfy maximal load conditions [9]. Also, it is estimated in Shuvalova [10] that 75% of the centrifugal pumps are oversized, many by more than 20%. In [PERSON] and [PERSON] [11], it is estimated that only 20% of the pump drive motors in operation are running at their rated mode. References [12,13] provide comparisons of energy consumption by a pump unit with electric motors of various types and IE classes with a VSD because the frequency adjustment provides significant energy savings, especially under a low load. Nevertheless, since the electric drives with a direct supply still prevail in many industries, a number of studies provide comparisons between characteristics of electric motors operating directly from the mains. For instance, [PERSON] and [PERSON] [14] provides a comparative analysis of the IM of the IE3 energy efficiency class and LSPMSM for fan applications in start-up and steady-state modes.