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Double squirrel cage rotor design is employed in induction motor applications that require high starting torque and high efficiency operation. The outer cage of double cage rotors is vulnerable to fatigue failure since it must withstand the large thermal/mechanical stresses experienced during a loaded startup due to the high starting current and long acceleration time. However, there are only a few publications that investigate broken bar detection for double cage induction motors. In this paper, the detectability of broken outer cage bars in double cage motors for the most commonly used rotor bar test methods is evaluated. A finite element and experimental study show that the sensitivity of on-line MCSA is significantly decreased, whereas that of off-line standstill tests is not influenced for broken outer cage bars. This suggests that one should be aware of the insensitivity of MCSA for double cage rotors, and there is a need for development of new on-line monitoring methods.

Electrowetting on dielectric (EWOD) is useful in manipulating droplets for digital (droplet-based) microfluidics, but its high driving voltage over several tens of volts has been a barrier to overcome. This article presents the characteristics of EWOD device with aluminum oxide (Al 2 O 3 , e r & 10) deposited by atomic layer deposition (ALD), for the first time as the high-k dielectric for lowering the EWOD driving voltage substantially. The EWOD device of the single-plate configuration was fabricated by several steps for the control electrode array of 1 mm 9 1 mm squares with 50 lm space, the dielectric layer of 1,270 Å thick ALD Al 2 O 3 , the reference electrode of 20 lm wide line electrode, and the hydrophobic surface treatment by Teflon-AF coating, respectively. We observed the movement of a 2 ll water droplet in an air environment, applying a voltage between one of the control electrodes and the reference electrode in contact with the droplet. The droplet velocity exponentially depending on the applied voltage below 15 V was obtained. The measured threshold voltage to move the droplet was as low as 3 V which is the lowest voltage reported so far in the EWOD researches. This result opens a possibility of manipulating droplets, without any surfactant or oil treatment, at only a few volts by EWOD using ALD Al 2 O 3 as the dielectric.