Biggest misunderstandings with 3 phase power......

[kwired]

Yep, that's about as clear as mud to a novice!

See what I reply with further down.

For an apples to apples comparison should it not be:
240x200x1.73 = 83,040 kW ????

I am using same VL-L for each. But I do get your point. It is less than double. Disappointing.

Why was I thinking times 3???? I wanted to think 3 times the power intuitively.

it is a factor of 1.732 which is less then double

Hello Mr. Dungar and all of the great contributors on this stellar forum.

I do understand the math I have been exposed to. However I believe if you really really grasp the subject it should be a wonderful mental challenge to develop a lucid abstraction for non analytical laymen that would enhance their depth of knowledge. That is the challenge I am putting out there for smart people like you who do understand their subject. I would be honored if you would go through the analogy I gave above and tell me why it is not useful or correct and lend me some guidance and help. If you can improve on it or present a totally different one I would be doing cartwheels.

My feeling is since no one gave me feedback directly on it, it must be totally deficient and even crazy. I have searched the web but cannot find a good answer. Feel free to start a new thread if you wish and I will contribute. Most electricians in the field are lost once you descend into the second or third level of detail. This I find very sad. This is just a genuine request, you do not have to reply since you owe me nothing. This is just a fun mental challenge that may help us all.

Do have a great Fourth......lots of celebration.

The problem I find with water/hydraulic analogy to try to explain electrical fundamentals is there is always something that doesn't completely translate. Though the analogy may be able to help one understand some there is usually some characteristic of hydraulics that just doesn't quite match electrical, and usually leaves the person you are trying to teach with a misunderstanding.

Three phase is not three single phase systems, it is one system with three major components for the source. Any three phase source derived from a phase converter is not a true three phase system it just acts like one in many ways.

 

[dionysius]

The problem I find with water/hydraulic analogy to try to explain electrical fundamentals is there is always something that doesn't completely translate. Though the analogy may be able to help one understand some there is usually some characteristic of hydraulics that just doesn't quite match electrical, and usually leaves the person you are trying to teach with a misunderstanding.

Can you describe just one specific scenario and give me and others a chance to see if what you say is valid. I am looking at phasor diagrams and asymmetrical loads and so far the fluid model is consistent. I will say that the phasor model (and it also is only a model) is extremely powerful. As line inductances are considered the angle between the phasors vary from 120 deg. As load imbalances are applied the neutral point starts to move in a circular path. It is no longer a fixed point.

In DC we all know the fluid analogy is excellent. All I am trying to do is extend it to AC. No rocket science here.

 

[jim dungar]

I have searched the web but cannot find a good answer.

Probably because a good answer does not exist.

You need to understand the math behind a waveform and then how waveforms add and subtract from each other.

If the discussion involves people totaly ignorant of the subject. Then do they really care if the analogy is not correct?

 

[Ingenieur]

Probably because a good answer does not exist.

You need to understand the math behind a waveform and then how waveforms add and subtract from each other.

If the discussion involves people totaly ignorant of the subject. Then do they really care if the analogy is not correct?

:weeping:

there is a reason why an EE essentially minors in math
12 calc credits
3 in linear algebra
3 in diff eq's
4 in prob/stat
and usually an elective, topology, computation, etc.

the 'answer' is derived by thinking in mathematical terms, not mechanical

 

[dionysius]

:weeping:
the 'answer' is derived by thinking in mathematical terms, not mechanical

There is no difference. The brain is neuroplastic. I taught myself calculus at a young age. I have some college where I studied applied mathematics. I remember spending hours and days in amazement with the number magic of Euler's almost surreal {e raised to the power of i times pie = 1}.

If you care to elaborate I am all ears. The example I can so well remember is when I learned all about angular momentum. I used the spinning top and bicycle wheel of my childhood to help me fully understand the math of gyros, gimbals, and Inertial Navigation which added accelerometers.

 

[Saturn_Europa]

The most common misunderstanding regarding three phase power I run into is the impression that in a balanced line the current in a phase conductor is 1/3 of the total current. That is, that if 150A of OCPD is needed, then it's a 50A fuse on each phase.

Correct me if I am wrong, but if the load is balanced across all three phases and 150 A of OCPD is needed than all three phases should be fused at 150 A.

 

[dionysius]

Probably because a good answer does not exist.

With all due respect, Jim, but that is a cop out. The answer exists, it is just that we have not tried hard enough. Had Einstein just accepted Newton's view he would not have bothered with General and Special Relativity and Gravitation.

 

[Ingenieur]

There is no difference. The brain is neuroplastic. I taught myself calculus at a young age. I have some college where I studied applied mathematics. I remember spending hours and days in amazement with the number magic of Euler's almost surreal {e raised to the power of i times pie = 1}.

If you care to elaborate I am all ears. The example I can so well remember is when I learned all about angular momentum. I used the spinning top and bicycle wheel of my childhood to help me fully understand the math of gyros, gimbals, and Inertial Navigation which added accelerometers.

Hogwash
psuedo intellectual gibberish, no offense
not talking about brain structure
talking about the physics of electricity and hydraulics
they are not the same
ask Bernoulli or Maxwell

in the hydraulic model there is no phase relationship
what is a resistor? Rough pipe, an orifice???
inductor, a 'paddle wheel'
a capacitor, a tank?

water has pressure and flowrate
AC electricity has voltage, current AND phase
it takes 2 formsf usage electric and magnetic fields
water only has pressure and mass flow rate
electrons are compressible
Q= C V, the higher the V the more for a fixed capacity
water is not compressable, regardless of pressure a fixed volume can't absorb more

the pressure drop across an orifice R or paddle wheel L is the same
both result in a loss of real power
but not in electricity

try having a mechanical engineer explain hydraulics using an AC electrical analogy lol

it's like trying to understand baseball by watching golf lol

 

[Ingenieur]

With all due respect, Jim, but that is a cop out. The answer exists, it is just that we have not tried hard enough. Had Einstein just accepted Newton's view he would not have bothered with General and Special Relativity and Gravitation.

That is the reality
whether you like it or not
btw who the heck are you to invalidate his answer?

are you comparing your model to relativity?

the science of electricity is well established
a hydraulic model will not provide a better understanding for those schooled in the subject

 

[ggunn]

Correct me if I am wrong, but if the load is balanced across all three phases and 150 A of OCPD is needed than all three phases should be fused at 150 A.

You are not wrong, and that was my point.

 

[ggunn]

With all due respect, Jim, but that is a cop out. The answer exists, it is just that we have not tried hard enough. Had Einstein just accepted Newton's view he would not have bothered with General and Special Relativity and Gravitation.

I don't see what the two have to do with each other. The problem with an analogy is that at the root of it it is just an analogy. If you examine it too closely it breaks down because you aren't talking about the thing, you are talking about some other thing that resembles the thing at a superficial level.

 

[dionysius]

the pressure drop across an orifice R or paddle wheel L is the same
both result in a loss of real power
but not in electricity

Electricity loses real power going through a resistor - it generates heat.

 

[Ingenieur]

Electricity loses real power going through a resistor - it generates heat.

But water losses it thru your 'inductor'
electricity doesn't
what about phase
does mass flow or volume have a delay or phase difference with the pressure it exerts?

your model is too complicated for me to understand
on top of that I don't see the need or use of it? The thought experiment
so bear with me and simplify it
assume 1 ph AC

Please provide the hydraulic circuit equivilents
generator, pump I assume: centrifugal, positive displacement?
type piston reciprocating, rotary lobe, progressive cavity
???

resistor, orifice, rough pipe????

inductor

capacitor

pipe for conductor is a given
pressure = voltage
pressure drop = voltage drop
flow Q = current
power, both real and reactive???
phase relationship pressure to Q

then we'll build a simpler model/ckt that even I can undstand
yhanks for you patience and indulgence

 

[Ingenieur]

I don't see what the two have to do with each other. The problem with an analogy is that at the root of it it is just an analogy. If you examine it too closely it breaks down because you aren't talking about the thing, you are talking about some other thing that resembles the thing at a superficial level.

making it fit distorts both
round peg into a square hole
it is better to actually talk about the 'thing'

 

[dionysius]

making it fit distorts both
round peg into a square hole
it is better to actually talk about the 'thing'

We must be very careful here. The "thing" we are talking about is only based on theory. No person has ever physically seen electrons. Science does convince us that the theory is correct and self-consistent today. Ten years from now the picture may change. It did for Newton. Thus every description of the "thing" is a model in a person's head and that includes the mathematical description. I feel that an open mind is important in this discussion. The analogy referred to by GGun applies to the above so listing the "thing" as an item we can talk directly about is not possible at this stage. Sorry folks but philosophy is very germane also to this discussion.

 

[Besoeker]

Electricity loses real power going through a resistor - it generates heat.

Converts would be a better description.

 

[Smart $]

...
You need to understand the math behind a waveform and then how waveforms add and subtract from each other.
...

The math is just an extension of the physics... so it doesn't hurt to understand the physics behind the waveforms.

 

[iwire]

We must be very careful here. The "thing" we are talking about is only based on theory. No person has ever physically seen electrons. Science does convince us that the theory is correct and self-consistent today. Ten years from now the picture may change. It did for Newton. Thus every description of the "thing" is a model in a person's head and that includes the mathematical description. I feel that an open mind is important in this discussion. The analogy referred to by GGun applies to the above so listing the "thing" as an item we can talk directly about is not possible at this stage. Sorry folks but philosophy is very germane also to this discussion.

This is more nonesense.

It is not that folks in this thread have a closed mind, it is that they have the knowledge to understand water does not behave like electricity and trying to say it does only confuses the person trying to learn the facts.

 

[Smart $]

We must be very careful here. The "thing" we are talking about is only based on theory. ...

Not theory in its entirety. In fact, only a small portion of the phenomena is theory. A good portion is fact. Do you think the world would be what it is electrically or electronically if all of it was just a theory?

 

[Ingenieur]

We must be very careful here. The "thing" we are talking about is only based on theory. No person has ever physically seen electrons. Science does convince us that the theory is correct and self-consistent today. Ten years from now the picture may change. It did for Newton. Thus every description of the "thing" is a model in a person's head and that includes the mathematical description. I feel that an open mind is important in this discussion. The analogy referred to by GGun applies to the above so listing the "thing" as an item we can talk directly about is not possible at this stage. Sorry folks but philosophy is very germane also to this discussion.

You must be careful
this is not 'theory'
these are physical laws, as in kcl and kvl
proven by experimentation and practice over 100's of years

your logic appears convoluted

you have dodged my question
provide electric/hydraulic equivilents
thanks

Electrons: although not 'seen' with the naked eye they have been 'seen' by other methods
as in filmed
this is a well understood science (by some, not me, lol)
https://blogearth.wordpress.com/2008/02/27/electron-filmed-for-the-first-time/