Electronics > Beginners
Will induction motors get replaced by synchronous motors?
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bonzer:
Hello everyone! Please give me your opinion about it. Will induction motors get replaced by synchronous motors? I'm attending a course about motors at university but we study synchronous motors only. At the same time I heard that induction motors are very popular even though less efficient. I'm afraid that anyway nobody's gonna replace them in near future in industrial environment, which is the domain where I'm gonna work and it feels like they aren't that popular in this case. That's why I hope I could understand them by my own...
rstofer:
Efficiency of induction motors has increased considerably over the last 40 years to the point that there is no financial incentive to change them to something else.  Coupled with a variable frequency drive, they can operate in unison with the demands imposed by the load.  This is a really big deal for HVAC heating/cooling water pumps and air handlers.  The MEs will always specified larger pumps and fans, the smart EE can recover from that.

Synchronous motors are used in industrial applications and, in particular, for large fixed loads like air moving fans or very large air compressors.  When used in these applications, the motor is often selected to improve plant power factor.  It is easier to control the field excitation if the load is nearly constant.  But I don't think you're going to see synchronous motors used for all applications throughout the plant.

Unless plant power factor is horrible, it is probably not financially possible to justify power factor correction with capacitors or synchronous motors.  Suppose your electric bill is, say, $8M/year and, of that, $20k is power factor penalty.  You would be far better off trying to optimize consumption rather than messing around trying to recover that penalty.  If you think you can fix things by 10%, well, 10% of $20k is $2k while 10% of $8M is $800k.  There's much more savings in reducing consumption.  There's also a bigger raise for having done so.  And, by the way, it's easier!
SeanB:
99% of electric motors in service are induction motors, the rest are a blend of universal motors, with synchronous motors only taking a tiny portion of that. Only place they are used almost exclusively is in mains synchronous clocks and microwave oven turntables, but even there they are being superseded by other types of motor. Only in the biggest older plants will you still find them, used for large loads and constant loads, where they find retrofitting a VFD too expensive for the age of the plant. Otherwise induction pretty much rules the roost, as you can get all of the advantages of a synchronous motor with an induction motor and an inverter of sorts, including energy recovery as a bonus during stopping, if you use a common DC bus for multiple inverters.
Zero999:
By synchronous motors are you talking about those with rare earth magnets, rather than those which require excitation? Yes, they're more efficient than induction motors, but are also a heck of a lot more expensive. Modern induction motors with copper, rather than aluminium bars in the rotor are almost efficient as rare earth magnet motors and I believe there has been some investigation into using them in electric vehicles.

Power factor is not an issue because large variable frequency drives include active power factor correction.
Kleinstein:
Induction motors are a lot easier to start than synchronous motors, that tend to need a special variable frequency drive at least for starting. Synchronous motors have advantages, like slightly higher possible efficiency but they also have disadvantages in many cases and they tend to be more expensive.  Synchronous motors / brushless motor may get attractive if there is speed control anyway.
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