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A question about Transformers

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It's also depending on the frequency of the AC voltage

if the frequency is close to man's avarage heart beat rate (60 a 70 Hz) than the chance it will disturb the heart beat is pretty big and more lethal than just a DC voltage with the same values

of course it starts all about 63V or higher (that's what I learned on school )

i normaly say every thing lower than 48 Volt is considered safe (not lethal) you still can burn your self and have a not so good time if you are a conductor for many amps at that voltage:D

Robert-Jan
 
It's also depending on the frequency of the AC voltage

if the frequency is close to man's avarage heart beat rate (60 a 70 Hz) than the chance it will disturb the heart beat is pretty big and more lethal than just a DC voltage with the same values

of course it starts all about 63V or higher (that's what I learned on school )

i normaly say every thing lower than 48 Volt is considered safe (not lethal) you still can burn your self and have a not so good time if you are a conductor for many amps at that voltage:D

Robert-Jan

Yes, I have heard the same thing, that frequency plays a big part. Evidently the lower frequencies are far more dangerous than the higher frequencies for the reason Robert mentioned. As far as AC or DC being more dangerous, I was tought DC is "potentially":)more harmful.
 
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That's why DC is used in welding and not AC. Because AC will just go through the metal and not arch like DC.

Larry

Ssshh! You'll give my AC-only 180A stick welder a complex, dude!

DC is used for various reasons: penetration, choice of positive or negative, easier arc control and a greater selection of rods are some. However, AC is still used and is still available on a lot of stick machines--it's easier to build an AC welder, and you don't have as many problems with arc blow.

AC arcs just fine. Ever seen the sparks in a power outlet when you unplug a fan while it's turned on?


Torben
 
Yes, I have heard the same thing, that frequency plays a big part. Evidently the lower frequencies are far more dangerous than the higher frequencies for the reason Robert mentioned. As far as AC or DC being more dangerous, I was tough DC is "potentially":)more harmful.

I don't have the "right" answer, but if the above is true (that lower frequencies tend to be more dangerous) then DC should be inherently more dangerous than AC since its frequency is 0. But I've also read the thing about near-heartbeat frequencies being dangerous because they confuse the heart.

This is interesting reading: https://en.wikipedia.org/wiki/Tesla_coil#The_.27skin_effect.27_and_high_frequency_electrical_safety

Whether AC or DC is worse, I don't really worry about. I'm with Leftyretro--treat it all with respect. Even if it won't kill directly, you can even start a fire with a 9V battery, or get a slight zap, jerk your hand back, and gash yourself on the sharp metal of the hard drive cage because you didn't turn off the computer before reaching in to plug in a fan (happened to me).


Torben
 
I don't know about starting fires. I imagine AC and DC are equally bad. DC only tends to be worse because the usual source is batteries which can provide huge currents. At higher voltages AC is probably worse because the peak voltage is higher than the RMS and dielectric heating also becomes a more significant factor.

As far as electricution is concerned I know for a fact that power line frequency AC is more worse than DC. For a start the peak voltage is 1.414 times higher (this should be pretty obvious) as it interferes with the heart beat more than DC.

How AC affects the body depends largely on frequency. Low-frequency (50- to 60-Hz) AC is used in US (60 Hz) and European (50 Hz) households; it can be more dangerous than high-frequency AC and is 3 to 5 times more dangerous than DC of the same voltage and amperage. Low-frequency AC produces extended muscle contraction (tetany), which may freeze the hand to the current's source, prolonging exposure. DC is most likely to cause a single convulsive contraction, which often forces the victim away from the current's source.

AC's alternating nature has a greater tendency to throw the heart's pacemaker neurons into a condition of fibrillation, whereas DC tends to just make the heart stand still. Once the shock current is halted, a "frozen" heart has a better chance of regaining a normal beat pattern than a fibrillating heart. This is why "defibrillating" equipment used by emergency medics works: the jolt of current supplied by the defibrillator unit is DC, which halts fibrillation and gives the heart a chance to recover.


The electrical code in the UK allows much higher DC voltages than AC voltages in situations where people might be electricuted e.g.

Any conductors with a greater potential difference (which respect to each other or earth) greater than 60VDC or 25VAC in a dry area or 30VDC or 12VAC in a wet area (damp skin is much more conductive than dry skin) need to be insulated from the user.

Any appliance with a only basic insultion between the user and the live parts does not require an earth conductor if it's operated with a voltage below 120VDC or 50VAC.

These aren't exact quotes, just what I can remember from the 17th edition of the wiring regulations.

I think this is a pretty dangerous myth which needs to be crushed as someone might incorrectly assume that 50VAC is pretty safe because 48VDC is and be electricuted as a result.
 
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I also have to agree AC is safer, IN A WAY. As alot of people know, say if you grab onto a peice of wire being fed AC, most people know that your muscles will contract, and cause you to grip the wire! With AC, you have a small chance of actually getting your hand off when the voltage is 0. With DC, there is no 0V point, so your hand is pretty much stuck there. AC is also dangerous in its own ways. like the heart fillibration stuff. AC is more likely to fillibrate your heart than DC, since its more like pulses. And also, AC arcs just as good as DC! Maybe the DC causing more fires/arcing was because there was no low point in the voltage, where the arc could possibly exinguish.

Interesting thread!
 
I also have to agree AC is safer, IN A WAY. As alot of people know, say if you grab onto a peice of wire being fed AC, most people know that your muscles will contract, and cause you to grip the wire! With AC, you have a small chance of actually getting your hand off when the voltage is 0.
Although you have a point this doesn't make as much difference as you might think because the zero crossing time is so short it doesn't give you much chance to let go.
 
T
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.

Transmission losses are much the same for DC and for AC at the same voltage.

AC is usually used because it is so much easier to transform the voltages with AC.

The power grid generators run at 35,000 volts or so, but the voltage is stepped up to 400,000 V or 132,000 volts for transmission on pylons, then down to 33,000 V, 11,000 V, and so on depending on what the final voltage is. All those voltage changes are much easier with AC.

AC motors are also simpler and can be made without brushes or electronics.

For undersea cables, the capacitance of the cable makes AC more lossy so DC is used, but at very high voltage. It also has the advantage that a DC link can join two networks of different frequencies or ones that are not synchronised.

https://en.wikipedia.org/wiki/HVDC_Cross-Channel
 
The reason AC is used is precisely because it has less loss and is easily transformed.
Transmission losses are much the same for DC and for AC at the same voltage.
Sorry guys but that's dog pucky! All things being equal in that we are talking about the same voltages and currents vis-à-vis RMS equivalence, then AC has more transmission losses than DC. Clearly you guys have never heard of AC Effective Resistance.

And in any case it's current not voltage that is often the higher function of specific losses due to I squared Z.
 
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I imagine AC and DC are equally bad.
Not so! In one major way DC is more difficult to work with.

Given the same heating effect when making the comparison, and given the same volts and amps when making the comparison, the DC arc will be herder to quench than the AC arc. Thus the switch gear and arc suppression must be more robust for the equivalent DC system.

Why you might ask? Because DC is steady state yet AC falls to zero twice per cycle.
 
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Interesting paper.
**broken link removed**
 
The transformer issue has been refined and optimized ad nauseum for over 125 years. There isn't much to discuss. BR.
How wrong you are! In fact magnetic amplifiers might make a comeback and magnetism itself is far from being fully understood.

"The magnetic amplifier is important to many phases of naval engineering because it provides a rugged, trouble-free device that has many applications aboard ship and in aircraft. These applications include throttle controls on the main engines of ships; speed, frequency, voltage, current, and temperature controls on auxiliary equipment; and fire control, servomechanisms, and stabilizers for guns, radar, and sonar equipment."

**broken link removed**
 
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How wrong you are! In fact magnetic amplifiers might make a comeback and magnetism itself is far from being fully understood.

hi,
As far as I am aware, they have never gone away..:rolleyes:
 
Interesting paper.
**broken link removed**

Thanks for that Mikebits. Kind of makes my point really.

Oh, and thanks for editing your previous post Chumly.
The email I got was:

Bull crap! All things being equal in that we are talking about the same voltages and currents vis-à-vis RMS equivalence, then AC has more transmission losses than DC. Clearly you have never heard of AC effective resistance.

I'm not sure why you felt the need for rudeness.
Yes, there is a lot of loss in AC power lines but if you read the link Mikebits posted you may understand why I was correct in what I said.

Larry
 
Oh, and Edison later patented the electric chair in order to show the danger in AC transmission. Just thought you might like to know.

Larry
 
Oh, and Edison later patented the electric chair in order to show the danger in AC transmission. Just thought you might like to know.

Not really true - there was an ongoing battle between Edison and Westinghouse - one DC and one AC. Both were trying to prove the others system was the most dangerous - including various barbaric displays in the streets. The invention of the electric chair was just another stunt to try and discredit the rivel system.

There's even a film about it, which is quite interesting.
 
Oh, and thanks for editing your previous post Chumly.
I changed it as soon as I realized that I posted before I editing.

I most often start with putting down general thoughts (sometimes pretty wild!) then editing them, but in this case I copy-pasted without edits as I half-asleep. Naturally I changed it very shortly thereafter.


Yes, there is a lot of loss in AC power lines but if you read the link Mikebits posted you may understand why I was correct in what I said.
Nope you are still incorrect when you said "The reason AC is used is precisely because it has less loss........"

As discussed you do not understand AC Effective Resistance.
 
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hi,
As far as I am aware, they have never gone away..:rolleyes:
Here is the definition of the word comeback: "A return to formerly enjoyed status or prosperity" and in that context they are not as popular as they once were and my post has merit.

Understand that the word comeback does not infer that the concern in question has "gone away" as you suggest above.

As discussed I said "magnetic amplifiers might make a comeback" and yes they were more popular by default as the alternatives were fewer!

Wiki says and I concur:

In later years, improved vacuum tubes, followed by the transistor, would come into play for the production and regulation of high-power AC and radio waves. Recently, however, a resurgence in the interest and applications of the magnetic amplifier is resulting in new uses for this venerable technology.

At one time, magnetic amplifiers were considered as an alternative to vacuum tubes because of their rugged construction, high reliability, and lower working voltages. Consequently, vacuum tubes had a definite lifespan due to heater filaments that eventually burned out over time, or a loss of vacuum resulting in potentially-destructive arc-overs within the tube.

Magnetic amplifiers were used early on to control large, high-power alternators by turning them on and off for telegraphy or to vary the signal for voice modulation. However, the alternator's frequency limits were rather low to where a frequency multiplier had to be utilized to generate higher radio frequencies than the alternator was capable of producing. Even so, early magnetic amplifiers incorporating powdered-iron cores were incapable of producing radio frequencies above approximately 200 kHz. Other core materials, such as ferrite cores and oil-filled transformers, would have to be developed to allow the amplifier to produce higher frequencies.

**broken link removed**)
 
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hi,
Thanks for the history lesson, but I was one of the engineers back in the 1950 and 60's working on industrial mag amp systems...:p

I have no need to read Wiki on this occasion.:)
 
hi,
Thanks for the history lesson, but I was one of the engineers back in the 1950 and 60's working on industrial mag amp systems...:p

I have no need to read Wiki on this occasion.:)
Fair enough, do you thus think the definition of comeback and the subsequent viewpoint to be incorrect?

In any case, and outside of such silliness, if you have any info in regard to the topic at hand, I would be more than pleased to read it and respond in kind.
 
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