A comparison of rotor bar material of squirrel-cage induction machines for efficiency enhancement purposes

This paper provides a comprehensive analysis and comparison of different rotor bar material in squirrel-cage induction machine from electrical, physical and economic perspectives in order to explore the impacts of rotor bar material on machine efficiency with physical and economic considerations. Specifically, aluminum, copper and silver are selected in this work and studied on three machines of different ratings, where silver is proposed as a hypothetical rotor bar material to open discussion and to explore potential possibilities. To provide an overall analysis, an analytical model and a finite-element model of an induction machine are used in this work with their focus on machine efficiency and magnetic flux distribution, respectively. It shows that a silver rotor can provide the highest efficiency under all tested loads and machines with efficiency enhancement of 0.20 to 1.55 percentage points compared to the aluminum counterpart depending on the machine rating and load. Moreover, better performance, such as larger output power, smaller starting torque, more concentrated magnetic flux distribution, etc., are observed with the increase of rotor bar conductivity. However, the significantly high price of silver could impede its usage in most applications currently and copper rotor bar is believed to have the overall superiority among the three kinds of material, although it suffers from casting issues due to its high melting points. Silver rotor bars or silver alloys may be used in energy-limited areas where high efficiency is needed to compete with certain magnetic material.