Abstract: An axial flow fan has a plurality of impeller blades spaced around a hub assembly. The leading edge of each blade overlaps completely the trailing edge of the preceding blade, and the angular spacing between the radial center lines of the blades is unequal, preferably varying in a sinusoidal pattern, so that tonal noise of the fan is effectively attenuated.

Abstract: A totally enclosed electrical machine, particularly a high power electric motor, is provided with a plate-type, crossflow, air-to-air heat exchanger which is seated on the frame of the electrical machine. Adjacent plates of the heat exchanger are modular units which define an array of ducts through which the internal air heated by the machine flows in a direction away from the machine. The ducts at opposite ends of the array provide passages for the bi-directional flow of air, such that air which is cooled in the heat exchanger is returned to the opposite ends of the machine. The heat exchanger is provided with a plenum in which air is returned to the end ducts. A baffle in the plenum distributes the air in different amounts, which vary progressively but in opposite senses, to the return ducts which communicate with the opposite ends of the machine thereby equalizing the temperature of the return air supplied to the opposite ends of the machine and providing uniform cooling of the machine.

Abstract: A system including an alternating current electric motor of the wound rotor type wherein the speed of the motor is controlled and its starting current is limited, is disclosed. A plurality of phase regulated SCR devices control the amount of resistance in the rotor winding circuits. A control voltage representing the difference between a desired motor speed and the actual motor shaft speed is supplied to an analog to digital converter which produces a multi-bit digital signal which controls the SCR devices so as to control rotor current in incremental steps. A vernier control signal is obtained by converting the digital signals back into analog form and comparing the control signal with the converted analog signal through the use of a difference amplifier circuit in a vernier amplifier.