Björn Bolund

Catch the wave to electricity

The ocean are largely an untapped source of energy. However, compared to other energies, power fluctuations for ocean waves are small over longer periods of time. This paper present a grid-oriented approach to electricity production from ocean waves, utilizing a minimal amount of mechanical components.

Experimental Results From an Offshore Wave Energy Converter

An offshore wave energy converter (WEC) was successfully launched at the Swedish west coast in the middle of March 2006. The WEC is based on a permanent magnet linear generator located on the sea f ...

Dielectric study of water/methanol mixtures for use in pulsed-power water capacitors

Large pulsed-power systems normally use a solid capacitive primary storage and a water capacitor for secondary storage. It is shown that the electrical breakdown strength is increased and the maximum storage time is enhanced from the microsecond level to the millisecond level when the water is replaced by a water/methanol mixture. The increased time scale in the second storage enables the use of an inductive primary storage. The mixing of methanol in the water decreases the relative permittivity. However, due to the increased electrical breakdown strength, a higher energy density is nevertheless possible. Previous work with water/ethylene glycol has manifested the problem of charge injection that occurs when energy is stored for millisecond time scales at high electrical stress. Water/methanol mixtures show less tendency for charge injection and a better ability to store energy at millisecond time scales.

Poynting Vector Analysis of Synchronous Generators Using Field Simulations

The Poynting vector has been used to gain an understanding of energy flow in rotating electrical machines. Previous studies of energy flow in rotating electrical machines have used the Poynting vector in crude formulas to obtain a qualitative picture. In this paper, we present a study based on numerically calculated fields and quantities entering the Poynting vector. We obtained a detailed understanding of how energy flows in the air gap and into the winding of a synchronous generator. In particular, we found that, at no-load, energy is flowing both to and from the stator as a result of cogging, while for normal load cases the energy flow is unidirectional.

Experimental results from an offshore wave energy converter

Anoffshore wave energy converter (WEC) was successfully launched at theSwedish west coast in the middle of March 2006. TheWEC is based on a permanent magnet linear generator locatedon the ocean flo ...

Rotor configuration impact on generator ventilation needs

Turbogenerators produce a vast portion of the electricity in the world. The cooling and ventilation required to take care of the excessive heat from the generators are costly. Simulations of three 20 MW/20 kV turbogenerators with approximately the same weight but with different stator and rotor configurations have been made. One conventional, one high voltage and one permanent magnet high voltage turbogenerator have been compared. Losses can be cut down considerably by, replacing the electromagnets on the rotor with permanent magnets and switch from an air-cooled stator to a water-cooled high voltage stator. Simulations show that for a 20 MW/20 kV turbogenerator the total losses can be cut down by up to 69% as compared to a conventional generator of the same size.

Poynting Theorem Applied to Cable Wound Generators

The use of cable windings in generators and transformers has a physical background which is hard to neglect. The work done by Maxwell, Poynting and Slepian combined with powerful finite element solver of today allows for visualization of electric and magnetic fields in different geometries. The electromagnetic fields and power flows for generator stator cables are in this article associated with Poyntings theorem. Geometrical design and insulation material properties are then linked to Poyntings theory showing that circular stator cables enable higher voltages while maintaining a high power flow. Today several high voltage generators and two transformers have been built and are currently in operation. This paper discusses the application of the Poynting Theorem to cable wound generators.