Measured Efficiency Improvements of Induction Motors with Thyristor/Triac Controllers

The deployment of inexpensive thyristor/triac controllers improve the efficiency and do not increase the power factor of induction motors (as measured at the input of pole transformer) operating under variable torque and constant speed constraints. Computer-aided testing yields detailed input/output powers for the drive. The improvement of the power factor does not increase the real-power capability (RPC) of a transformer supplying power to such drives due to current harmonics. Although the total harmonic current distortion (THDi) may exceed IEEE 519 and IEC 555 recommendations, recent publications show that the impact on the apparent power derating of a 25 kVA pole transformer is small if the THDi is less than 50%.