Characteristics of Collective Losses of Squirrel Cage Induction Motors used in Pumping Units

Energy efficiency of water pumping systems is an issue that has recently been addressed by many authors. Complexity of this issue involves the need to combine energy efficiency of two separate systems which interact with each other: a water supply system and a power system. This paper presents a new non-intrusive method for calculation the efficiency of a squirrel-cage induction motor that is part of a pump unit. The pump control system determines operation of the pumping station operation point and hence its efficiency. It is assumed that there is a generalized estimated characteristic of the motor efficiency, which being a component of the control system, will be used for selection of the pumping system rotational speed change range. Rotational speed has a direct impact on the motor load torque, the pump output and the head, hence, the motor efficiency. Authors have defined collective losses across a squirrel-cage motor. Hellwig's statistical method has been employed to determine the characteristic estimating collective losses based on experimental testing of 21 motors with power up to 2.2 kW. Simulation and experimental results are used to check the validity and performance of the proposed method. The main advantages of the method is its simplicity of use and minimal data requirements.