A question about Transformers

[Muhammad89]

HI everyone,


We all know the fact that transformers can transform only AC voltages from one level to another but not DC just basically because the transformer has no a moving part, however, since DC produces much magnetic field than AC isnt it really much adequate to use DC instead of AC to produce highly effecient Transformers that would be likely to save energy losses? and that would simply , as I think, be done by applying a moving part to the transformer. what do you think of this idea.


Muhammad89

 

[Claude Abraham]

A static (dc) field produces zero induction. That's a law that cannot be skirted. It is not a matter of choice. AC is the only option.

Low ac frequencies incur less loss than high ac frequencies, but the transformer must be physically larger and heavier for low frequency operation. There are always tradeoffs. The transformer issue has been refined and optimized ad nauseum for over 125 years. There isn't much to discuss. BR.

 

[arrie]

Muhammad, I think take your answer from what claude stated.
The only reason I'm posting this is to try and get your reasoning.

What do you mean by a moving part?

 

[rezer]

Hello again Muhammad,

In order for there to be induction, you must have a varying magnetic field that cuts across the conductors. This is what causes voltage to be induced. Unlike a generator that rotates the conductors to cut across the magnetic fields. But this is the same principle. Maybe this is what you meant by "...but not DC just basically because the transformer has no a moving part,...". There has to be motion for there to be induction.

 

[Muhammad89]

Muhammad, I think take your answer from what claude stated.
The only reason I'm posting this is to try and get your reasoning.

What do you mean by a moving part?

since DC is Zero Frequency, I meant to rotate the liminated slides of the transformer, which in turn will become a moving part simutanously with feeding the transformer with the DC. That, in my opinion result in transforming DC from 1 level to 2 level without the need of converting it into AC.

Muhammad89

 

[Larry4911]

Muhammad, you are missing the point I think. Either the conductor or the magnetic field must move through each other to induce an EMF. In your case you are probably on the way to thinking a motor could be used to power a generator.
But it cannot be done because of losses and inefficiency in both the motor and generator.

Larry

 

[arrie]

So you want to rotate the core?

If that's what I understand it will be a first. But again I believe it'll have no effect. Your transformer has two sides, a primary and secondary. As the current starts to flow in the primary, say from zero to I-max, a magnetic field is induced in that conductor, and this field cuts the secondary conductor, producing a current in it, although no physical connection exist between secondary and primary.
Remember, a current will still be induced in the secondary conductor, even if no steel core is used, it referred to as air core.
The function of the steel core is to intensify the flux. Spinning it will probably have no benefit, except to cut your coils.
So, at any point that only a static current flows through the primary coil, nothing will happen in the secondary coil, like 0V reading will be taken. It has to change, magnetic flux has to cut the conductor to induce current flow.

Hope it helps

 

[Muhammad89]

So you want to rotate the core?

If that's what I understand it will be a first. But again I believe it'll have no effect. Your transformer has two sides, a primary and secondary. As the current starts to flow in the primary, say from zero to I-max, a magnetic field is induced in that conductor, and this field cuts the secondary conductor, producing a current in it, although no physical connection exist between secondary and primary.
Remember, a current will still be induced in the secondary conductor, even if no steel core is used, it referred to as air core.
The function of the steel core is to intensify the flux. Spinning it will probably have no benefit, except to cut your coils.
So, at any point that only a static current flows through the primary coil, nothing will happen in the secondary coil, like 0V reading will be taken. It has to change, magnetic flux has to cut the conductor to induce current flow.

Hope it helps

I think you chased alot of blues away of my mind as I was thinking that the steel core was the source of the induction. (Hope it helps) hehe, your hope is fulfilled and it helped so profoundly. Thank you all for the clarification.

Muhammad89

 

[arrie]

Glad to have been of help to someone today.
Go well

 

[Larry4911]

To add to what Claude said.
As an electrician myself I feel qualified enough to explain one or two things.

The transmission of DC mains has been tried by a number of distribution networks many, many years ago. At the beginning Thomas Edison's network was DC. However the dangers inherent in distributing a high DC current is impossible to condone. It's just too dangerous. Not to mention the losses inherent in DC power lines it's just stupid. I haven't got the exact figures but, to get 100v DC out 20 miles away you would have to feed the lines with something like 1000volts. It's to dangerous and expensive.

The reason AC is used is precisely because it has less loss and is easily transformed.

If you had a DC transformer with a moving core, even if it was possible, for EG. You would have a lot of loss just turning the core. So, you have already defeated the purpose.

Larry

 

[Muhammad89]

To add to what Claude said.
As an electrician myself I feel qualified enough to explain one or two things.

The transmission of DC mains has been tried by a number of distribution networks many, many years ago. At the beginning Thomas Edison's network was DC. However the dangers inherent in distributing a high DC current is impossible to condone. It's just too dangerous. Not to mention the losses inherent in DC power lines it's just stupid. I haven't got the exact figures but, to get 100v DC out 20 miles away you would have to feed the lines with something like 1000volts. It's to dangerous and expensive.

The reason AC is used is precisely because it has less loss and is easily transformed.

If you had a DC transformer with a moving core, even if it was possible, for EG. You would have a lot of loss just turning the core. So, you have already defeated the purpose.

Larry

Thanks Larry for the explanation, it went abit out of the topic about the possibility of having a DC transformer, as I am now fully convinced it is impossible to have such Transformers. my great thanks to all of the experts and technicians on this chat.
Muhammad89

 

[Larry4911]

I know it was of topic a bit. I thought you might appreciate the reason why AC is used for transmission lines and house mains. In reference to transformers.

Larry

 

[Muhammad89]

I know it was of topic a bit. I thought you might appreciate the reason why AC is used for transmission lines and house mains. In reference to transformers.

Larry

I really and so greatly appreciate it Larry, I agree on almost all you mentioned about AC transmission and why it is prefered over DC except on your saying that DC is Much Dangerous than AC because however much the DC current is, the same amount ,but of AC is far much dangerous,however,much costy.

Muhammad89

 

[arrie]

After all, that is what transformers are about, get power to places, and turn it into something useful for appliances.
I love transformers and magnetism.
Great stuff.

For interest sake, did you know, as you drive your car with its fixed rear axle, the axle actually have the potential to provide a very small amount of power from cutting earth's magnetic field.
Who would have thought.

But don't get excited, it's minuscule. Just interesting

 

[rezer]

I really and so greatly appreciate it Larry, I agree on almost all you mentioned about AC transmission and why it is prefered over DC except on your saying that DC is Much Dangerous than AC because however much the DC current is, the same amount ,but of AC is far much dangerous,however,much costy.

Muhammad89

AC more dangerous than DC? Now that sounds like it deserves a different thread. Any takers? I'm sure many will debate this point and it really depends on who you're asking.

 

[Larry4911]

except on your saying that DC is Much Dangerous than AC because however much the DC current is, the same amount ,but of AC is far much dangerous,however,much costy.

Muhammad89

Your wrong there. DC is much more dangerous. I don't mean for the body. I mean for short circuit faults. Have you ever dropped a spanner across a fully charged car battery. No, well I have. It's not pretty. DC shorts can take your arm off. AC will just hurt or if your unlucky kill you at the same currents. That's why DC is used in welding and not AC. Because AC will just go through the metal and not arch like DC.

DC caused too many fires and that's why it's not used in transmission lines.

Larry

 

[arrie]

rezer, I'm sure it will depend on 10 types of takers.
But I'll cast my vote for AC being safer.

But make no mistake, both can kill you easily. Your heart only requires 35mA to make it on or off, depending on its current state.

 

[Larry4911]

But make no mistake, both can kill you easily. Your heart only requires 35mA to make it on or off, depending on its current state.

I don't know where you got that titbit. But it only takes 6mA AC across the heart to stop it. I think you mean 35ma between arms maybe.

However my point was DC is much more likely to cause fires and sparking than AC at the same currents.

Larry

 

[Muhammad89]

I don't know where you got that titbit. But it only takes 6mA AC across the heart to stop it. I think you mean 35ma between arms maybe.

However my point was DC is much more likely to cause fires and sparking than AC at the same currents.

Larry[/QUOT



Ooooooh, I see

Muhammad89

 

[Leftyretro]

At the same potential and impedance, the safety concerns for AC or DC should be considered equivalent. Respect both as neither care a bit about your safety

Lefty