You are correct non PM wind generators had many transmissions failures. Have you ever asked why? It was a basic design flaw in the system design that had nothing to do with alternator type.
Lets look at wind Generators and their history Wind generators started to really gain a footing in the late 80s early 90s. At this time it was very hard to switch high voltages and currents at hi speed with solid state devices. So all wind generators were 60 HRZ. 60 HRZ power needed a transmission to drive the alternator at either 1800 RPM or 3600 RPM to create 60 HZ . Blade speed had to be constant. It was easy to change blade angle to maintain speed with slow wind velocity changes. The idea was to use the Grid as a large flywheel to take up sudden changes in Wind speed. Unfortunately this meant with a sudden puff the grid had to absorb power to slow blades until angle could be changed. When puff dissipated the grid had to supply power to keep blade speed constant until blade angle was change . Everything stayed same speed. The sudden changes in power flow direction put tremendous stress on gears resulting in early failure.
The only example I can think of is, the throttle on your car sticks open. You decide to get home by doing speed control by turning ignition key on and off. Your speed will be ok but the stress on transmission as the engine goes from producing power to absorbing it will damage your drive train if done for a long time. This is what happened with the early non PM designs. It was not a
generator type problem it was a design architecture problem. There was no way to efficiently convert to DC then back to fixed AC when these first came out.
Two things happened about the same time. High frequency, high voltage, high current, Solid state devices had some amazing advances. PM design took off. The wind generators went from generating 60 HZ to generating variable frequency high voltage AC converting this to a high voltage DC then using a solid state inverter to generate the 60 HZ AC to feed to the grid. The transmission problems had nothing to do with PM or no PMs in the Alternator. PM designs have momentum so they will stay PM for a while but if something happens they can go back to non PM and there will be no transmission because the non PM will generate variable frequency high voltage AC just like PM alternators do today. Assembly lines, spare parts technician training will keep wind alternators a PM design until something motivates change. Please also note from the alternator in your car to the one in power stations to the one in the small generators for homes no other alternators have moved to PM designs. Wind generators are the only power generating devices that PM alternators have a foot hold. This had nothing to do with PM or Non PM alternators. It had to do with a major design problem with fixed frequency Alternators being driven by something as variable as the wind. This problem no longer exists.
I apologize to countries that use 50HRZ I know they do exist just here it is 60.
Most PM motors need brushes! The field is fixed by magnets not current. Induction motors have never had brushes even 75 years ago. DeWalt in the US recently dropped most of their PM motors in battery hand tools. Milwakee tools is doing the same thing but is not as far along as Dewalt. Dewalt replaced PM motors in the XR series. Look up the Dewalt XR, they make a big deal out of the fact new Inductions motors have no brushes. Google it. These tools have longer battery life much better speed control Higher torque. Wider speed range. The one thing I do not like is the XR series is heavier by about 15 ~20 %.
Your saying induction motors have brushes shows a basic misunderstanding of how motors work and leaves me to question your understanding of the pros and cons of both types. (in fact you seem to think PM good, no PM bad). The changing field in the stator of an induction motor inducts a current in the rotor of the induction motor with no electrical connection (brushes), just
https://seekingalpha.com/article/41...y-ramp-limitation-ahead-battery-manufacturing magnetic. No field changes with a perm magnet so changing fields have to be induced other ways. Brushes are the most common and simplest way but not the only way.
Induction motors use to run at one speed only. Had very poor starting torque. Most motors had to use Capacitors to distort input (change phase angle) just to start. Modern induction motors use solid state controllers. The controllers create a variable frequency output so the motor can run over a very wide RPM range. The wave form looks nothing like a sine wave allowing for massive torque even at zero RPM. This is why Tesla uses induction motors in all their vehicles except model 3. Note that PM motors in EVs and hybrids require a transmission. Induction motors do not need transmission even for stop and reverse. Tesla S P90D with the LSU option. Uses an induction motor does zero to 60 in 2.8 Seconds top speed 155MPH (intentionally limited) all without a transmission. Model 3 with a PM Motor also has very impressive specs but there is a simple transmission. Of course the model 3 has lots of bugs. If it had an induction motor I am sure many on this board would blame that. I do not feel it is related to the PM motor just a continuation of Tesla’s Quality problems.
https://seekingalpha.com/article/41...y-ramp-limitation-ahead-battery-manufacturing
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