Fortsätt till huvudinnehåll

Inlägg

Visar inlägg från februari, 2014

[VAWT] Second test

There were some issues during the first tests due to that the output voltage from the generator was too low. The generator voltage can be raised by using a gearing factor n that increases the rotational speed and therefore the EMF voltage by 
EMF = n*k*w
where k is the motors voltage constant and w is the wind turbine's rotational speed. The generator will spin faster and therefore generate more voltage, simply put. 



When a gearing is introduced the torque on the generator's rotor is also decreased. This reduces the copper losses 
Ploss,copper = r*I^2 ~ r*(T/(k*n))^2 
as the current I is directly proportional to the torque T, and inversely proportional to a theoretical motor constant k, in theory. Lower rotor torque thus means that the copper losses are reduced. 
Reluctance effects However, the BLDC motor used is affected by quite a lot of  reluctance effects. An initial torque of a certain level is needed to overcome the reluctance effects and the motor then rotates a step. Th…

[VAWT] Plausible improvements of the Savonius windmill

Cut a barrel in half, mount it on a shaft and you have a windturbine. If the barrel is used, then what else probably would end up on a scrap heap is instead used for converting renewable energy.

Simplicity and low cost makes this an attractive option especially for societies with limited economy and a malfunctioning or non existing electric grid. Small off-grid electrical networks can be built and people who perhaps most needs electricity get that. Isn't that neat?


Savonius (from http://solarvan.co.uk/savonius)

An overlooked potential?
The Savonius though has a widespread reputation of having low effiency and is often dismissed as a credible option around forums and in formal litterature. However, when looking at the graph below from a publication Wortman did 1983, the effiency can be realtively high provided that the TSR(Tip-to-Wind-Speed-Ratio) is held at a correct value and the windmill should work quite nicely. In practice this could probably be done by controlling the generato…