Potential Transformer

[Kit Talich]

Hello all!

I am currently working on my senior design project of a Digital
Power Meter here at the South Dakota School of Mines and Technology
(Shamless plug!). I plan to measure and display Voltage, Current, Power
and Power Factor. To do this I plan to sample both waveforms and
calculate the rest. I have found a Hall Effect type current sensing
chip. While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can
find some of these? Small size would also be desired.


P.S.: Gimme a JOB! B.S. EE minor:CSC

 

[Ian Stirling]

Hello all!

I am currently working on my senior design project of a Digital
Power Meter here at the South Dakota School of Mines and Technology
(Shamless plug!). I plan to measure and display Voltage, Current, Power
and Power Factor. To do this I plan to sample both waveforms and
calculate the rest. I have found a Hall Effect type current sensing
chip. While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can

If it's isolated from the user, and double insulated, a simple resistive
divider may work well.

 

[John_H]

Why use a voltage transformer if high-value resistors work? just make sure
you keep within the power and voltage constraints on the resistors in a
resistor divider and you can sample within the range of your A/D converter.
Easy!

 

[John Popelish]

Hello all!

I am currently working on my senior design project of a Digital
Power Meter here at the South Dakota School of Mines and Technology
(Shamless plug!). I plan to measure and display Voltage, Current, Power
and Power Factor. To do this I plan to sample both waveforms and
calculate the rest. I have found a Hall Effect type current sensing
chip. While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can
find some of these? Small size would also be desired.

Is that a request for a 230V to 10V PT? Are you willing to use an
ordinary 10 volt step down transformer with a 230 volt primary? Is 9
volts out close enough?

If so, you might look at some toroidal transformers with dual
primaries (115-230). They have quite good voltage regulation under
light load.
http://rocky.digikey.com/WebLib/Amv...Series Low Profile Miniature Transformers.pdf

 

[Joerg]

Hello Kit,

... While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can
find some of these? Small size would also be desired.

Buy them in Europe. Everything is 230V there. You can also buy current
transformers (make sure to never, never leave the burden resistors off).

Regards, Joerg

 

[Rich Grise]

Hello all!

I am currently working on my senior design project of a Digital
Power Meter here at the South Dakota School of Mines and Technology
(Shamless plug!). I plan to measure and display Voltage, Current, Power
and Power Factor. To do this I plan to sample both waveforms and
calculate the rest. I have found a Hall Effect type current sensing
chip. While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can
find some of these? Small size would also be desired.


P.S.: Gimme a JOB! B.S. EE minor:CSC

If you want to measure potential, how about a - may I have a drum roll
please - voltage divider and ADC?

You _do_ have a common ground reference, haven't you?

Good Luck!
Rich

P.S.: Employ me, and I'll help you reassimilate into Real Life. ;-)

 

[Phil Allison]

Hello all!

** Beware - gmail and Google Groupie !!!

I am currently working on my senior design project of a Digital
Power Meter here at the South Dakota School of Mines and Technology
(Shamless plug!). I plan to measure and display Voltage, Current, Power
and Power Factor. To do this I plan to sample both waveforms and
calculate the rest. I have found a Hall Effect type current sensing
chip. While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can
find some of these? Small size would also be desired.

** Where did the "10A" come from ??

Or did you mean to say V ?

A small toroidal transformer would be ideal to derive a scaled and isolated
AC supply voltage - but do not use it for powering the device sine the
addition of a rectifier circuit will clip the waveform.



......... Phil

 

[Phil Allison]

"John Popelish"

If so, you might look at some toroidal transformers with dual primaries
(115-230). They have quite good voltage regulation under light load.

** That last bit looks like a tautology.



............ Phil

 

[Pooh Bear]

If you want to measure potential, how about a - may I have a drum roll
please - voltage divider and ADC?

You _do_ have a common ground reference, haven't you?

How about a patent on that ?

Graham

 

[John Larkin]

Hello all!

I am currently working on my senior design project of a Digital
Power Meter here at the South Dakota School of Mines and Technology
(Shamless plug!). I plan to measure and display Voltage, Current, Power
and Power Factor. To do this I plan to sample both waveforms and
calculate the rest. I have found a Hall Effect type current sensing
chip. While I have found a few 120V-5V PT's my personal requirements
are 230V 10A. Potential Transformers that accomplish this feat seem to
be a little more rare. Does anyone out there know of somewhere I can
find some of these? Small size would also be desired.

Use a resistibe voltage divider. Or a series resistor into a small
audio-type transformer, operated in current mode. Or any ole 240-to-6
or whatever transformer. You'll probably have to to a phase tweak
somewhere in the system anyhow.

P.S.: Gimme a JOB! B.S. EE minor:CSC

Gimmie a resume!

John

 

[Phil Allison]

"John Larkin"

Use a resistibe voltage divider. Or a series resistor into a small
audio-type transformer, operated in current mode. Or any ole 240-to-6
or whatever transformer. You'll probably have to to a phase tweak
somewhere in the system anyhow.

** Using "any ole" transformer is bad advice.

Small E core mains transformers have high and non linear magnetising
currents - so the output waveform is distorted and does not follow input
voltage changes linearly. There is often significant phase shift as well.

Small mains toroidal generally have no such issues.




.......... Phil

 

[John Popelish]

"John Popelish"






** That last bit looks like a tautology.

It is pretty close, as long as the core is no where near saturation.
If it is near saturation, a slight change in voltage or frequency can
change the input to output ratio. When dealing with instrumentation
instead of power transformers, you have to be more flexible with the
concept of regulation than just load current regulation. ;-)

 

[John Popelish]

"John Larkin"





** Using "any ole" transformer is bad advice.

Small E core mains transformers have high and non linear magnetising
currents - so the output waveform is distorted and does not follow input
voltage changes linearly. There is often significant phase shift as well.

Small mains toroidal generally have no such issues.

Agreed. That is why I offered an example of a toroidal, 50-60 Hz
transformer.

 

[Phil Allison]

"John Popelish"

It is pretty close, as long as the core is no where near saturation. If it
is near saturation, a slight change in voltage or frequency can change the
input to output ratio. When dealing with instrumentation instead of power
transformers, you have to be more flexible with the concept of regulation
than just load current regulation. ;-)

** That is purest gobbledegook.

The term "voltage regulation" when referring to transformer is related to
load.

The term you needed and should have used was was " voltage linearity" .




......... Phil

 

[Phil Allison]

"John Popelish"

Agreed. That is why I offered an example of a toroidal, 50-60 Hz
transformer.

** Shame you gave a fallacious reason.

Good thing the true one is now posted.





.......... Phil

 

[John Larkin]

"John Larkin"



** Using "any ole" transformer is bad advice.

Small E core mains transformers have high and non linear magnetising
currents - so the output waveform is distorted and does not follow input
voltage changes linearly. There is often significant phase shift as well.

The magnetizing current waveform couples weakly to the secondary
voltage waveform. And any electric meter winds up needing some phase
tweak somewhere anyhow, as noted.

Small mains toroidal generally have no such issues.

What makes a toroid different?

John

 

[Phil Allison]

"John Larkin"
"Phil Allison"

The magnetizing current waveform couples weakly to the secondary
voltage waveform.

** Not true of most small E-cores.

Your knowledge of them is sadly lacking too.

" Small E core mains transformers have high and non linear magnetising
currents - so the output waveform is distorted and does not follow input
voltage changes linearly. "

And any electric meter winds up needing some phase
tweak somewhere anyhow, as noted.

** Not much help when the phase shift is varies with applied voltage.

What makes a toroid different?

** Very low Imag when used within ratings.





......... Phil

 

[John Larkin]

"John Larkin"
"Phil Allison"


** Not true of most small E-cores.

Your knowledge of them is sadly lacking too.

How many electronic electric meters have you designed and sold? I'm
running about 5000 so far.

" Small E core mains transformers have high and non linear magnetising
currents - so the output waveform is distorted and does not follow input
voltage changes linearly. "





** Not much help when the phase shift is varies with applied voltage.

AC line voltage hardly changes. It's the CT that has the serious
phase-versus-current problem, which can be electronically compensated
to some extent.

** Very low Imag when used within ratings.

Any core can be run at low Imag. The shape doesn't matter.

John

 

[Phil Allison]

"John Larkin"
"Phil Allison"

How many electronic electric meters have you designed and sold?

** Big noting yourself like this does not work with me.

In fact, it makes you look like a pathetic jerk.

AC line voltage hardly changes. It's the CT that has the serious
phase-versus-current problem, which can be electronically compensated
to some extent.



Any core can be run at low Imag. The shape doesn't matter.

** You are quite wrong, yet again, plus missing the point entirely and as
usual.

The point related to using " any ole " transformer".

Remember those words ??

How quickly you do forget.



......... Phil

 

[John Larkin]

** Big noting yourself like this does not work with me.

Why would I care how I look to you? What matters is that the money's
still in the bank.

** You are quite wrong, yet again, plus missing the point entirely and as
usual.

You might be a tad more specific. So how does the shape of the core
affect the available Bmax?

The point related to using " any ole " transformer".

Remember those words ??

Sure. Most any AC power transformer will make a decent PT for
metering. Even a little distortion doesn't matter much, if you do the
math. Besides, if it's approaching magnetic saturation, and if its
primary copper loss is so high that significant secondary distortion
results, it will run hot without load. I suppose there may be wall
warts this bad, but it would be pretty rate.

And this is a school project... it doesn't have to be qualified to
ANSI C12, as my meters were.

John