Complex Imaginary Exam 1 Prob 8- synch motors

[ElecPwrPEOct11]

Hi. I want to make sure I 100% understand this answer. The CI explanation isn't enough.

The solved problem states that synchronous motors of any frequency, current, or mechanical load should be run in an optimal zone of operation. This zone is: shaft rotation speed range above peak torque.

In trying to understand this answer I realized I didn't have a torque vs speed graph for synch motors in any of my resources. I found one here: http://catalogo.weg.com.br/files/wegnet/WEG-synchronous-motors-technical-article-english.PDF

Here's how I reason through the answer- by running the motor above the speed at peak torque, you are ensuring the motor operates at synch speed. Letting the speed drop below peak torque would rapidly decelerate the motor causing it to stall. Is this reasoning correct? Does this same theory apply to induction machines (except you don't operate at exactly synch speed)? Thanks for help with these basics.

 

[ElecPwrPEOct11]

Bump. Can someone help me understand this?

 

[DK PE]

Their statement seems a little confusing to me. When a synchronous motor is running properly, increases in torque will not cause the rpm to change until the load torque reaches the "pull-out" spec value and then you will stop. In a cage motor, increases in load (torque) will result in more slip --> less rpm --> higher current until something bad happens.

I think your interpretation of the their statement and the speed/torque curve is conceptually correct.

 

[ElecPwrPEOct11]

Thanks for the response. Sounds like I'm thinking about this right.