Electrical Energy

[Danijel Gorupec]

On 9/3/2018 at 4:36 PM, studiot said:

By placing the windings in slots they are actually moved out of the position of maximum field.

However if the armature was smooth and the windings were on the surface, there would be considerable sideways force generated on them (it's still there in the slots) so they would tend to slip sideways.

It doesn't matter that the windings are out of the most intense part of the field because they still cut the same number of field lines.

The slots are there to stop the sideways slip and hold the windings in place.

 

Sorry for being late, but I thought it might be insightful to invoke some caution regarding the above reasoning.

The fact that windings in slots are out of the position of maximum field is, I would say, an understatement. Indeed, I feel it would be better to say that windings in slots are in position of insignificant field. All the iron that surrounds the wires acts as a good magnetic shielding - iron takes the large majority of the flux and very little of it actually goes through wires. As a result, the majority of motor torque cannot develop in the wires - and it is not that wires are pushing on the iron and turn the rotor around.

Of course, placing windings into slots helps them not to slip sideways (it also helps fasten them against much more significant centrifugal forces). In addition, it enables motors with narrower air gap - if placed on the surface, wire dimensions would add to the air gap (and, as Studiot said, immersed into considerable field of the air gap they would then also feel considerable sideways forces).

The third quoted sentence is the debatable one... A current-carying wire develops a force proportional to the field it is immersed into. The idea of 'number of filed lines it cuts' might come useful sometimes, but to me it seems somehow artificial (and confusing). It is just the field 'through' the wire and the current in the wire that counts (actually, it is just the quantity and velocity of electrons and the field density and its direction at their path). As the filed density is quite low inside deep motor slots, so the wire there cannot feel much force - no matter how much field lines it cuts.

The majority of rotor torque must be generated in the iron itself - in rotor 'teeth', specifically. The purpose of the rotor winding is to generate field gradient where 'teeth' are immersed into... This is how I see the torque generation in a modern electric motor... You might get quantitatively good enough results if you just make calculations where you simply multiply rotor winding current and field density in the iron (or in the air gap, but not in the slots where winding actually is). However, such a procedure does not describe what actually is happening inside and might confuse a student who tries to think rigorously.
 

[Theredbarron]

29 minutes ago, Danijel Gorupec said:

The majority of rotor torque must be generated in the iron itself - in rotor 'teeth', specifically. The purpose of the rotor winding is to generate field gradient where 'teeth' are immersed into... This is how I see the torque generation in a modern electric motor... You might get quantitatively good enough results if you just make calculations where you simply multiply rotor winding current and field density in the iron (or in the air gap, but not in the slots where winding actually is). However, such a procedure does not describe what actually is happening inside and might confuse a student who tries to think rigorously.

 

Is it the higher up the teeth the more immersed? Is this all pretty much to reduce Eddie currents?

[studiot]

51 minutes ago, Danijel Gorupec said:

Sorry for being late, but I thought it might be insightful to invoke some caution regarding the above reasoning.

The fact that windings in slots are out of the position of maximum field is, I would say, an understatement. Indeed, I feel it would be better to say that windings in slots are in position of insignificant field. All the iron that surrounds the wires acts as a good magnetic shielding - iron takes the large majority of the flux and very little of it actually goes through wires. As a result, the majority of motor torque cannot develop in the wires -1  and it is not that wires are pushing on the iron and turn the rotor around.

2   Of course, placing windings into slots helps them not to slip sideways (it also helps fasten them against much more significant centrifugal forces). In addition, it enables motors with narrower air gap - if placed on the surface, wire dimensions would add to the air gap (and, as Studiot said, immersed into considerable field of the air gap they would then also feel considerable sideways forces).

3   The third quoted sentence is the debatable one... A current-carying wire develops a force proportional to the field it is immersed into. The idea of 'number of filed lines it cuts' might come useful sometimes, but to me it seems somehow artificial (and confusing). It is just the field 'through' the wire and the current in the wire that counts (actually, it is just the quantity and velocity of electrons and the field density and its direction at their path). As the filed density is quite low inside deep motor slots, so the wire there cannot feel much force - no matter how much field lines it cuts.

The majority of rotor torque must be generated in the iron itself - in rotor 'teeth', specifically. The purpose of the rotor winding is to generate field gradient where 'teeth' are immersed into... This is how I see the torque generation in a modern electric motor... You might get quantitatively good enough results if you just make calculations where you simply multiply rotor winding current and field density in the iron (or in the air gap, but not in the slots where winding actually is). However, such a procedure does not describe what actually is happening inside and might confuse a student who tries to think rigorously.
 

Don't forget what I said was very broad brush and compact.

 

1) I am sorry if what I wrote led you to think that I meant the wires were pushing the rotor. Thiswas not a description to the working of a motor, but the answer to a question Why do we bother with slots?

2) Yes slots have several advantages. My comment was about what would happen if we did not have them.

3) Well I would like to see your mathematics that supports this view. I would suggest wire, embedded or not, passes through the whole of the flux generated by the stator pole, in passing from one meshing point to the next. Therefore the EMF generated will be the same, embedded or not.

10 minutes ago, Theredbarron said:

Is it the higher up the teeth the more immersed? Is this all pretty much to reduce Eddie currents?

See my comment.

[Theredbarron]

On ‎9‎/‎3‎/‎2018 at 7:36 AM, studiot said:

By placing the windings in slots they are actually moved out of the position of maximum field.

However if the armature was smooth and the windings were on the surface, there would be considerable sideways force generated on them (it's still there in the slots) so they would tend to slip sideways.

It doesn't matter that the windings are out of the most intense part of the field because they still cut the same number of field lines.

The slots are there to stop the sideways slip and hold the windings in place.

 

The solution to eddy currents is sheet or segmental construction since the eddy conduction path is broken at every interface.

However there is a cost-benefit assessment to be made becasue the thinner the laminations the more expensive they are.

 

The principle of brake testing applies to all rotary machinery, I had thought you would be interested.

 

 

Sorry was it this part? So no matter where they are aligned the same field lines are cut from the iron?

That's it for eddie currents? pretty much gone from the laments

[Theredbarron]

Is it possible to use the Eddy currents as an advantage?

Are there any other types of armatures out there or is this the issue?

[Theredbarron]

So is it possible to induce eddy currents without alternating in a conductor making the electrons in the mass move in one direction allowing electrons to be pulled from the other end of the conductor sort of turning the conductor into a capacitor that pulls electrons instead of pushing them or change the polarity and have them push electrons around? To control this flow would be diodes.

[studiot]

The point here is that the electrical mechanism of operation of transformers and electric machinery is complicated and not a one step process.

This is (perhaps) why Dima was right to observe that many textbooks skate over this issue rather delicately.

I mentioned transformers as they are easier to understand than motors or generators so I would always start with them first.

[Theredbarron]

I was thinking about using gas for a rotor. On another thread we were discussing static electricity a bit. I want to attempt to stimulate the air and extract the static electricity from it. Is there anything on eddy currents and static electricity?

[John Cuthber]

53 minutes ago, Theredbarron said:

Is there anything on eddy currents and static electricity?

Yes.

Since eddy currents are only caused by changes in magnetic fields (and thus by changes in currents) but static electricity is- definitively- static...

static electricity can not give rise to eddy currents.

[Theredbarron]

22 minutes ago, John Cuthber said:

Yes.

Since eddy currents are only caused by changes in magnetic fields (and thus by changes in currents) but static electricity is- definitively- static...

static electricity can not give rise to eddy currents.

Another question I have abut static electricity is will it produce o3 if its not creating an electrical arc? More of when the exchange of electrons between molecules as it creates the static electrical energy is what I'm referring to. 

[Danijel Gorupec]

21 hours ago, studiot said:

3) Well I would like to see your mathematics that supports this view. I would suggest wire, embedded or not, passes through the whole of the flux generated by the stator pole, in passing from one meshing point to the next. Therefore the EMF generated will be the same, embedded or not.

From the context of your post I figured that you were referring to the force/torque generation, not the EMF generation... If indeed your were referring to the EMF generation, then yes, depicting 'number of lines cut' can be an acceptable pedagogical approach. The number of field lines cut is indeed a good illustration of the flux change (which is what generates the EMF)... However using 'number of lines cut' to explain force/torque generation, would in my opinion just make more confusion than explanation.

[studiot]

23 minutes ago, Danijel Gorupec said:

From the context of your post I figured that you were referring to the force/torque generation, not the EMF generation... If indeed your were referring to the EMF generation, then yes, depicting 'number of lines cut' can be an acceptable pedagogical approach. The number of field lines cut is indeed a good illustration of the flux change (which is what generates the EMF)… 

So why do you think I wrote this?

21 hours ago, studiot said:

Therefore the EMF generated will be the same, embedded or not.

 

24 minutes ago, Danijel Gorupec said:

 However using 'number of lines cut' to explain force/torque generation, would in my opinion just make more confusion than explanation.

How many more times do I have to say I didn't so use it.

The explanation was very very clearly directed at the "question why are there slots?"

[Danijel Gorupec]

27 minutes ago, studiot said:

How many more times do I have to say I didn't so use it.

Don't get mad so quickly. If I misunderstood, I am sorry. The torque is generated as well in a generator as it is in a motor so I could not know what are you referring about if you mention both, EMF and torque, in the same post.

[studiot]

2 minutes ago, Danijel Gorupec said:

Don't get mad so quickly. If I misunderstood, I am sorry. The torque is generated as well in a generator as it is in a motor so I could not know what are you referring about if you mention both, EMF and torque, in the same post.

Of course we want torque, and I have already offered my route to it.

 

4 hours ago, studiot said:

The point here is that the electrical mechanism of operation of transformers and electric machinery is complicated and not a one step process.

This is (perhaps) why Dima was right to observe that many textbooks skate over this issue rather delicately.

I mentioned transformers as they are easier to understand than motors or generators so I would always start with them first.

Seeing this again, I realise I also owe you an apology since I have confused you with a different member I called Dima.

[Theredbarron]

Okay so the whole reason for alternating current from what I understand is to make the electrons have a continual flow correct? If this is so then I would have to make an Armature and a stator because I want to use parallel magnetic fields. This rotor and stator are going to be for power generation but an attempt to create direct current only. Not the gas one that I was talking about. I will still have to use diodes to maintain it's Direction. I'm assuming that this is kind of a problem trying to make direct current only. I thought about that and how just applying a positive field to a conductor only attracts the electrons to that location. So I'm going to move the positive field but it has to be from the inside of a conductor. This is where I want to attempt to make an eddy current. If I can attract the electrons from the inside of a metal tube on one end causing a flow of current on the same end attracting the electrons from the other end. Sort of a twisting and squeezing effect on the electrons from the inside of the conductor.

[Strange]

Note that there are also DC motors and DC generators: https://www.electricaleasy.com/2012/12/basic-construction-and-working-of-dc.html

AC is used for motors in the house and factory because there is an AC supply. The motors in automobiles, for example, are DC motors. (I think it is easier to control torque and speed precisely with DC motors - but that may just be because I have only seen controllers for DC motors when working in automotive.)

[Theredbarron]

33 minutes ago, Strange said:

Note that there are also DC motors and DC generators: https://www.electricaleasy.com/2012/12/basic-construction-and-working-of-dc.html

AC is used for motors in the house and factory because there is an AC supply. The motors in automobiles, for example, are DC motors. (I think it is easier to control torque and speed precisely with DC motors - but that may just be because I have only seen controllers for DC motors when working in automotive.)

Correct cars do use DC what the alternator uses alternating current then rectifies it to make DC.

 I know they have DC generators but they alternate the fields in the Armature as far as I understand.

[studiot]

AC motors and generators are used in preference to DC in vehicles, boats and aircraft because they are smaller and lighter than the equivalent DC version.

This characteristic is inversely propostional to the frequency of generation with DC = 0 and the weight/size decreasing as frequency increases (aircraft use 400 cycles)

Ac also allows for polyphase equipment.

[Theredbarron]

15 minutes ago, studiot said:

AC motors and generators are used in preference to DC in vehicles, boats and aircraft because they are smaller and lighter than the equivalent DC version.

This characteristic is inversely propostional to the frequency of generation with DC = 0 and the weight/size decreasing as frequency increases (aircraft use 400 cycles)

Ac also allows for polyphase equipment.

I do agree that AC Motors are much better also for power generation. DC generators don't have to rectify what's coming out because the contacts only touch the part of the windings of the Armature that are receiving that polarity of magnetic field from the stator. the alternating current portion of a DC generator is only happening in the Armature. I want to make one that creates DC that doesn't alternate current from the rotating shaft all the way out to the output leads. This would be why I need to remake the Armature as far as I can tell. Technically I won't have a stator because I won't have coil windings.

[studiot]

DC from generator is not like DC from a battery.

DC generators also have a commutator to swith the polarity.

No stator windings?

 

On 05/09/2018 at 5:05 PM, studiot said:

The point here is that the electrical mechanism of operation of transformers and electric machinery is complicated and not a one step process.

 

[Theredbarron]

The input to a DC generator is either a magnet or an electromagnet in the stator position. I want to input at the Armature and output at where the stator would be.

[studiot]

2 hours ago, Theredbarron said:

The input to a DC generator is either a magnet or an electromagnet in the stator position. I want to input at the Armature and output at where the stator would be.

How does that avoid two sets of windings?

I can't see you making a 1kw generator with permanent magnets.

[Theredbarron]

54 minutes ago, studiot said:

How does that avoid two sets of windings?

I can't see you making a 1kw generator with permanent magnets.

I'm not using permanent magnets. I was describing what regular DC generators have. My stator will be a solid conductor in the shape of a tube with the Armature inside it. The Armature will only use positive field to attract the electrons in this conductor to create a current much like an eddy current on one end of the tube. whether or not I have a coil on the tube I'm still deciding

[Theredbarron]

Sort of like heating element logic accept I'm using a tube so It can direct the flow in a circle on the one end creating a differential across the distance of the tube. How thick the tube is, the strength of the magnetic field, and the air gap are all going to be at play here still. The differential will be perpendicular to the flow. The further down the tube the more differential. I think the thickness of the tube is going to effect total power. What I want to avoid is the reversing of current to make it easier to continue current flow if that makes any sense. 

[studiot]

16 hours ago, Theredbarron said:

My stator will be a solid conductor in the shape of a tube with the Armature inside it. The Armature will only use positive field to attract the electrons in this conductor to create a current much like an eddy current on one end of the tube. whether or not I have a coil on the tube I'm still deciding

I'm having trouble picturing this

solid and tube?

Do you mean single conductor?

Perhaps a sketch?