The inverse rule for designing reluctance motor - its educational and industrial advantages

Asynchronous machines and synchronous machines belong to the most popular AC drives which are characterized by completely different torque-speed curves. After supplying directly from 3-phase voltage system an asynchronous machine is able to overcome load and to reach the nominal speed approximately equal to the synchronous speed. The synchronous machine after supplying leaves at standstill and cause of this state is absence of positive average torque. The problem of missing starting torque is usually solved by equipping the rotor of a synchronous motor with a starting squirrel-cage which is located in pole faces. The commonly-used design rule for a synchronous reluctance motor is: design a reluctance motor developing main reluctance torque and then equip its rotor with a squirrel-cage producing missing starting torque. In this paper “inverse rule” is proposed which relies on contrary reasoning. Its essence is: take an induction motor producing starting torque and remove some iron parts in a rotor for exposing main reluctance torque. This “inverse rule” has important value from educational point of view because it teaches students flexibility and versatility in design process. It is very helpful in developing non-conventional approach to solve engineering tasks because it shows (in evident and convincing way) that in the commonly-known object can be hidden new unexpected possibilities related to quite different requirements. Design consideration was verified by construction of the prototype and by laboratory investigations.