An exemplary power system may include an electric machine with multiple sets of stator windings, each set of windings being coupled through a separate switch matrix to a common voltage bus, and each of which may be spatially arranged in full pitch around the stator such that stator flux harmonics are substantially reduced. The reduced stator flux harmonics may be associated with phase current harmonic content. In an example application, such power systems may operate in a generating mode to transfer mechanical energy to electrical energy on a DC voltage bus. In some illustrative embodiments, the power system may provide both high-power and high-speed (e.g., 1MW at 8000 rpm or above) motoring and/or generating capability suitable, for example, for on-board (e.g., marine, aviation, traction) power systems.

Electromechanical energy conversion systems

Pump as turbine – A pico-hydro alternative in Lao People's Democratic Republic

The invention relates to a cooling-arrangement of an electrical machine. The inventive arrangement for cooling of an electrical machine comprises a rotor (1) and a stator (2) of the electrical machine, while an air-gap (AG) is between the rotor (1) and the stator (2). The electrical machine (G) comprises an air-cooling-arrangement (7), which circulates air inside the electrical machine (G). The electrical machine (G) comprises an liquid-cooling-arrangement (8,9,10,11,12), which circulates cooling-liquid (12) inside the electrical machine (G). The air-cooling arrangement (7) and the liquid-cooling-arrangement (8,9,10,11,12) are connected by an air-to-liquid heat-exchanger (8), which is applied to transport heat out from the electrical machine (G) by the cooling-liquid.

Arrangement for cooling of an electrical machine

Implementations of mini hydro schemes with conventional hydraulic, electrical equipment's and controllers have proven very expensive and uneconomical. Many developing countries that are in need of rural electrification have encountered economical problem when setting up these mini hydro schemes. To address this problem, alternative options and new designs of these equipment's have been explored by many researchers around the world. The application of these new designs would reduce the overall cost of mini hydro development and would help in making it a cost effective technology. These new designs will also help developing countries to provide electricity to rural areas or remote regions where interconnection of transmission line from the electrical grid is uneconomical. The new designs can also be an enabling factor in boosting up electricity generation using a renewable energy source. This paper provides survey of all these alternative options and new designs in the controller, hydraulic turbine and generators that have been implemented in different countries of the world.

A comprehensive overview of new designs in the hydraulic, electrical equipments and controllers of mini hydro power plants making it cost effective technology

A wind power installation includes a nacelle, and energy conversion system for converting wind power into electric energy. The energy conversion system includes a heat-generating source which is disposed in the nacelle and constructed to include a closed primary cooling system using air for dissipating generated heat. Further provided is an open secondary cooling system which uses ambient air for cooling heated air from the primary cooling system.

Wind power installation with separate primary and secondary cooling circuits

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. External air is directed through channels between adjacent plates of the heat exchanger, the opposite sides of which define the ducts for the internal machine air. The entire unit can readily be assembled at low cost.

Totally enclosed air cooled electrical machines

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.

Axial flow fan

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. During start up, when the motor is brought up to speed and until the motor speed is close to the predetermined speed, the digital signal from the analog to digital converter is inhibited causing the SCR-resistor current paths in the rotor winding circuits to become open circuited. Another SCR-resistor vernier path which is connected to the rotor windings is operated by the vernier control signal to control the rotor current so as to provide for smooth low current starts as well as to control current in the rotor windings between the digitally controlled incremental steps.

Alternating current motor system

Induction generators are seeing increasing use for energy recovery applications because of their inherent simplicity and ease of connection to an electrical power system. Often questions concerning induction generator control considerations are presented. These include power system short-circuit contribution, automatic reclosure after a power outage, power factor correction, system startup, and self- excitation. Induction generator applications and control considerations often encountered are addressed, and some answers and ideas are provided for the engineer planning an induction generator energy recovery system.

Herbert W. Thode

Papers

Totally enclosed air cooled electrical machines

Axial flow fan

Alternating current motor system

Typical Applications of Induction Generators and Control System Considerations

Axial flow fan impeller