Abstract
Energy efficiency of systems of water pumping is a complex problem since efficiency of two distinct interacting systems needs to be combined: water and power supply. This paper introduces a non-intrusive method of calculating the so-called “collective losses” of a cage induction motor. The term “collective losses”, which the authors define, allows for accurate estimation of motor efficiency. Control system of a pump determines operating point of a pumping station, and thus its efficiency. General estimated performance characteristics of a motor, components of a control system, are assumed to serve selection of a range of pumping speed variations. Rotational speed has a direct effect on motor load torque, pump power and head, and thus on motor performance. Hellwig’s statistical method was used to specify characteristics of estimated collective losses on the basis of experimental studies of 21 motors rated at up to 2.2 kW. The results of simulations and experiments are used to verify validity and efficiency of the suggested method. The method is non-intrusive, simple to use, and requires minimum data.
Highlights
Analysis of energy efficiency of a water plant system is complex
Collective losses are defined on the basis of a Sankey diagram, Explaining variables necessary for a multiple regression model are determined on the basis of relative collective losses, Hellwig’s method is adapted to eliminate those explaining variables that have less significant impact on the estimated collective loss function—the estimated model is simplified, Coefficients, components of the predicted variable, are determined
The rotor hysteresis losses Physr are ignored because: f s f r. Such an assumption is correct for pump and fan load torque that reduces in line with the squared rotational speed in accordance with affinity laws
Summary
Analysis of energy efficiency of a water plant system is complex. Variations of plant output pressure and efficiency of pump and motor must be addressed. Use of motor equivalent circuit parameters, study of influence of slip on motor efficiency, measurement of current and voltage in stator winding, measurement of rotational speed and torque, analysis of no-load or load motor parameters, calculation of air gap torque—AGT method, efficiency optimizations techniques. These methods generate results which estimate efficiency of induction motors only after performing additional investigations accurately or effectively. They all need no-load losses and stray losses to minimize the estimated efficiency error.
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