# Help with this practice final on motor control principles and power control...

#### blazedaces

Joined Jul 24, 2008
130
Attached below is the practice final exam provided for us to study. I'm having a lot of trouble and would appreciate any and all help please.

I went through the practice final and was able to answer many questions, but still many elude me. If you could help me with any of the following I would very much appreciate it. Thank you.

4) For this I believe it has something to do with assuming the functions are linear since I know the superposition principle requires this assumption, but I'm not 100% sure that's a satisfactory answer...

10)?

14) I believe the answers are as follows, but if someone could verify this for me and if I'm wrong please explain why: a) slip increases, b) Ir decreases, c) Wsync decreases

18) I believe this is Air Gap Power, but again I'm not 100% sure of myself on it.

22)?

26)?

29 and till the end (excluding the last extra credit about how many labs we do of course) I'm really not sure. I looked up some stuff about power controls, but I'm not sure if the general information matches what he wants us to know. I have to apologize the reason I'm really fuzzy on the answers in this section is because I missed the last week of classes when this was covered. Still, I would like to try and learn anything I can now before the final. Thanks, I appreciate the help.

Thanks for any and all help again,

-blazed

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#### t_n_k

Joined Mar 6, 2009
5,448
Guessing the missing word is always fun.

I'll try Q. 29

a. Thyristor (SCR), b. GTO Thyristor, c. MOSFET, d. IGBT

Is thyristor OK twice ....? I'll throw in mercury arc thingy for old times sake.

I don't want to be selfish with this.

#### blazedaces

Joined Jul 24, 2008
130
Guessing the missing word is always fun.

I'll try Q. 29

a. Thyristor (SCR), b. GTO Thyristor, c. MOSFET, d. IGBT

Is thyristor OK twice ....? I'll throw in mercury arc thingy for old times sake.

I don't want to be selfish with this.
I know he says "controllable switches", but I'm not sure if he means types of switches, like you're referring to, or if he wants an answer like this:

a) AC-AC
b) AC-DC
c) DC-AC
d) DC-DC

I'll memorize both just in case

Edit: I looked over the info I found again, and you're most probably right...

#### t_n_k

Joined Mar 6, 2009
5,448
How did you go with the rest of the one's you weren't sure of?

Q.26 I'd suggest (b) - neither (a) or (c) seem logical. I imagine the momentary speed increase is associated with the field collapse and the stopping would be consistent with there being no field available to sustain motor shaft torque.

Q.22 - that would be a series motor.

Q.18 - not sure myself - your answer makes sense but I assume the second part would be minus losses - stator losses etc.

Q.14 - (a) yes, the slip would increase, (b) the rotor current would probably increase to accommodate the increased shaft load, (c) well the true synchronous speed is set by the mains frequency and motor pole no. - the actual shaft speed would decrease slightly given (a) and (b)

Q.10 - the high magnetising inductive reactance?

Q.4 - I think you're right - for instance perhaps the magnetic circuit must not be operating in the saturation region for example ...?

not sure if I've been of any help.

#### blazedaces

Joined Jul 24, 2008
130
How did you go with the rest of the one's you weren't sure of?

Q.26 I'd suggest (b) - neither (a) or (c) seem logical. I imagine the momentary speed increase is associated with the field collapse and the stopping would be consistent with there being no field available to sustain motor shaft torque.

Q.22 - that would be a series motor.

Q.18 - not sure myself - your answer makes sense but I assume the second part would be minus losses - stator losses etc.

Q.14 - (a) yes, the slip would increase, (b) the rotor current would probably increase to accommodate the increased shaft load, (c) well the true synchronous speed is set by the mains frequency and motor pole no. - the actual shaft speed would decrease slightly given (a) and (b)

Q.10 - the high magnetising inductive reactance?

Q.4 - I think you're right - for instance perhaps the magnetic circuit must not be operating in the saturation region for example ...?

not sure if I've been of any help.
Thanks a lot for your help. I appreciate it.

-blazed