Welcome, Guest. Please login or register.

November 23, 2019, 08:48:41 am

Author Topic: What's the difference with a commutator in a generator, motor and alternator  (Read 6162 times)  Share 

0 Members and 1 Guest are viewing this topic.

you0006

  • Victorian
  • Trendsetter
  • **
  • Posts: 101
  • Respect: 0
So many definitions, my brain has gone boom!!

Lasercookie

  • Honorary Moderator
  • ATAR Notes Legend
  • *******
  • Posts: 3175
  • Respect: +323
To clarify first:
A motor is when we have the current and field already - so the coil ends up spinning.
A generator/alternator is when we have the rotating coil and field already - so the current is induced.
We use split ring commutators and slip rings in different situations.

Split ring commutator in a motor: Every half turn, the forces would all point outwards, disrupting the motion of the coil. So the current is reversed every half turn, allowing the forces to return to a maximum and allowing the rotation to continue in the same direction.

Note: if we use A.C. current, we don't need the brushes to reverse the current.

Split ring commutator in a generator: Produces D.C. as the split ring 'rectifies' the EMF produced.

Slip ring in an alternator: Produces A.C. Does not mess with the current produced by the coil.

A bit basic but these are the key things to remember. I hope I didn't miss anything.

Shark 774

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 261
  • Respect: +1
To clarify first:
A motor is when we have the current and field already - so the coil ends up spinning.
A generator/alternator is when we have the rotating coil and field already - so the current is induced.
We use split ring commutators and slip rings in different situations.

Split ring commutator in a motor: Every half turn, the forces would all point outwards, disrupting the motion of the coil. So the current is reversed every half turn, allowing the forces to return to a maximum and allowing the rotation to continue in the same direction.

Note: if we use A.C. current, we don't need the brushes to reverse the current.

Split ring commutator in a generator: Produces D.C. as the split ring 'rectifies' the EMF produced.

Slip ring in an alternator: Produces A.C. Does not mess with the current produced by the coil.

A bit basic but these are the key things to remember. I hope I didn't miss anything.

Agreed. Laseredd: What do you think is necessary in explaining slip rings? Do you think it's necessary to mention that they are used to avoid tangling of wires which would happen if wires were used, or do you think saying that they don't change the current direction is sufficient?

Lasercookie

  • Honorary Moderator
  • ATAR Notes Legend
  • *******
  • Posts: 3175
  • Respect: +323
Agreed. Laseredd: What do you think is necessary in explaining slip rings? Do you think it's necessary to mention that they are used to avoid tangling of wires which would happen if wires were used, or do you think saying that they don't change the current direction is sufficient?
I would vary my answer as according to the question and how many marks have been allocated. For VCAA 2010, the marks that would have been allocated to the slip ring portion (if I remember correctly, it asked what is the difference between the slip ring and the split ring commutator - pretty sure it was 3 marks)

My approach was something like:
  • Split ring commutator is used in a generator, produces D.C.
  • How it functions in a generator (alternates the contact every blah blah blah)
  • Slip rings are used in an alternator (produces A.C.) and maintain the same contact with blah blah blah

As you can see, you run out of space to mention the tangling stuff. I would consider the facts mentioned there are more significant.

If it was a 3 mark question asking only about the function of the slip ring, then I would go ahead and mention the fact that it reduces entanglement. Probably look something like this:
  • Slip rings are used in an alternator and produces A.C.
  • How it does that (maintain the same contact with blah blah blah)
  • Slip rings are used to prevent entanglement blah blah blah

If you go back and study the assessor reports, the entanglement reason seems to be a bit excluded.


edit: fixed formatting

b^3

  • Honorary Moderator
  • ATAR Notes Legend
  • *******
  • Posts: 3530
  • Overloading, just don't do it.
  • Respect: +627
  • School: Western Suburbs Area
  • School Grad Year: 2011
Agreed. Laseredd: What do you think is necessary in explaining slip rings? Do you think it's necessary to mention that they are used to avoid tangling of wires which would happen if wires were used, or do you think saying that they don't change the current direction is sufficient?
I would vary my answer as according to the question and how many marks have been allocated. For VCAA 2010, the marks that would have been allocated to the slip ring portion (if I remember correctly, it asked what is the difference between the slip ring and the split ring commutator - pretty sure it was 3 marks)

My approach was something like:
  • Split ring commutator is used in a generator, produces D.C.
  • How it functions in a generator (alternates the contact every blah blah blah)
  • Slip rings are used in an alternator (produces A.C.) and maintain the same contact with blah blah blah

As you can see, you run out of space to mention the tangling stuff. I would consider the facts mentioned there are more significant.

If it was a 3 mark question asking only about the function of the slip ring, then I would go ahead and mention the fact that it reduces entanglement. Probably look something like this:
  • Slip rings are used in an alternator and produces A.C.
  • How it does that (maintain the same contact with blah blah blah)
  • Slip rings are used to prevent entanglement blah blah blah

If you go back and study the assessor reports, the entanglement reason seems to be a bit excluded.


edit: fixed formatting
Are we actaully allowed to use it as a reason? I've never come across it over two textbooks (altough one is a jacaranda one) and exam before.
2012-2016: Aerospace Engineering/Science (Double Major in Applied Mathematics - Monash Uni)
TI-NSPIRE GUIDES: METH, SPESH

Co-Authored AtarNotes' Maths Study Guides


I'm starting to get too old for this... May be on here or irc from time to time.

Shark 774

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 261
  • Respect: +1
+1
Agreed. Laseredd: What do you think is necessary in explaining slip rings? Do you think it's necessary to mention that they are used to avoid tangling of wires which would happen if wires were used, or do you think saying that they don't change the current direction is sufficient?
I would vary my answer as according to the question and how many marks have been allocated. For VCAA 2010, the marks that would have been allocated to the slip ring portion (if I remember correctly, it asked what is the difference between the slip ring and the split ring commutator - pretty sure it was 3 marks)

My approach was something like:
  • Split ring commutator is used in a generator, produces D.C.
  • How it functions in a generator (alternates the contact every blah blah blah)
  • Slip rings are used in an alternator (produces A.C.) and maintain the same contact with blah blah blah

As you can see, you run out of space to mention the tangling stuff. I would consider the facts mentioned there are more significant.

If it was a 3 mark question asking only about the function of the slip ring, then I would go ahead and mention the fact that it reduces entanglement. Probably look something like this:
  • Slip rings are used in an alternator and produces A.C.
  • How it does that (maintain the same contact with blah blah blah)
  • Slip rings are used to prevent entanglement blah blah blah

If you go back and study the assessor reports, the entanglement reason seems to be a bit excluded.


edit: fixed formatting

Yeah I've noticed that in their reports, just wondering what you're opinion was. Cheers.
Agreed. Laseredd: What do you think is necessary in explaining slip rings? Do you think it's necessary to mention that they are used to avoid tangling of wires which would happen if wires were used, or do you think saying that they don't change the current direction is sufficient?
I would vary my answer as according to the question and how many marks have been allocated. For VCAA 2010, the marks that would have been allocated to the slip ring portion (if I remember correctly, it asked what is the difference between the slip ring and the split ring commutator - pretty sure it was 3 marks)

My approach was something like:
  • Split ring commutator is used in a generator, produces D.C.
  • How it functions in a generator (alternates the contact every blah blah blah)
  • Slip rings are used in an alternator (produces A.C.) and maintain the same contact with blah blah blah

As you can see, you run out of space to mention the tangling stuff. I would consider the facts mentioned there are more significant.

If it was a 3 mark question asking only about the function of the slip ring, then I would go ahead and mention the fact that it reduces entanglement. Probably look something like this:
  • Slip rings are used in an alternator and produces A.C.
  • How it does that (maintain the same contact with blah blah blah)
  • Slip rings are used to prevent entanglement blah blah blah

If you go back and study the assessor reports, the entanglement reason seems to be a bit excluded.


edit: fixed formatting
Are we actaully allowed to use it as a reason? I've never come across it over two textbooks (altough one is a jacaranda one) and exam before.

I've only noticed it on khan academy videos, but yeah that's basically the only reason they use it, otherwise they would just use wires.

Lasercookie

  • Honorary Moderator
  • ATAR Notes Legend
  • *******
  • Posts: 3175
  • Respect: +323
+1
Are we actaully allowed to use it as a reason? I've never come across it over two textbooks (altough one is a jacaranda one) and exam before.
Come to think of it - that's a good point, the textbooks don't mention it as far as I remember either. It may not actually be on the study design. My teacher told us that it was one of the reasons that a slip ring would be used over bare wires (it seems logical - if it's not changing anything, why use it?). 

But yeah, like I said, if we do get a three mark question on slip rings, I'll mention tangled wires as a third point. I would anticipate a slip ring only question (they did identify last year that students did poorly when talking about slip rings), but VCAA tends to be fairly boring and consistent with their exams.


Edit: Actually, why use it is quite obvious. The coil is rotating. You need the EMF it's creating. The output end of the alternator is not rotating. You need the slip ring to make the connection from the rotating coil to the stationary output. Arguably, it's the same point as not tangling the wires, but I think it's better worded (thanks Wikipedia).
« Last Edit: October 25, 2011, 11:08:26 pm by laseredd »