Impact of Number of Rotor Slots on Performance of Three-Phase and Single-Phase Induction Machines

As it is well known, a number of rotor slots have a strong impact on an induction machine. A number of rotor bars have to be chosen correctly with respect to pole pairs and number of stator slots. If this part of machine design is made incorrectly final machine may suffer from parasitic torques. Influence of these parasitic torques may be so strong that the machine is unusable even if other parts of the design are well done. There is usually more combination of stator and rotor slots with a similar impact on parasitic torques than just one. Due to this, it is possible to choose a number of rotor bars with respect not only to parasitic torques but also with respect to other properties of a machine such as efficiency. But the number of slots is also limited by sizes of a machine. Too many rotor slots lead to thin both bars and teeth which could cause complications during a manufacturing process. This issue is especially connected with small machines. A usable number of rotor slots is limited by a technology of manufacturing process and number of their stator slots is usually small due to the same reason. Therefore, possibilities how to influence small induction machine performance are not so wide as in big ones and have to be studied carefully. This article deals with an impact of number of rotor bars on performance both small there and single-phase induction machines.