DC Standstill Torque Used to Measire Lq of Reluctance and Synchronous Machines

An experimental method for measuring the quadrature axis inductance (Lq) of polyphase synchronous machines is developed. It is based on a measurement of developed torque with the rotor at standstill and with the stator winding supplied with dc currents. While applicable to all synchronous machines, it is developed and explained for reluctance motors primarily. Special techniques are used to minimize measurement errors due to hysteresis and due to air gap permeance harmonics. Detailed results are presented for one reluctance motor which has a highly variable Lq, and correlation with other methods is found to be quite good. The effects of saturation are observed, and Lq is found to depend on quadrature axis current in the tested motor, with direct axis current having a slight effect on Lq at larger currents.