Batteryless current clamps?

[John Larkin]

On Thu, 19 Nov 2009 10:27:34 -0800 (PST), George Herold
<ggherold@gmail.com> wrote:

On Nov 19, 11:40 am, John Larkin
jjlar...@highNOTlandTHIStechnologyPART.com> wrote:
On Thu, 19 Nov 2009 07:29:26 -0800, Fester Bestertester <f...@fbt.net
wrote:

So, for a millivolt output probe, this might be as simple as 2 windings (or a
tapped single winding) with a range switch to select the winding?

Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.

Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.

Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.

http://en.wikipedia.org/wiki/Rogowski_coil

The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.

http://www.gmw.com/electric_current/Danfysik/866_867/867.html

John


Wiki's great thanks John. That second link didn't have much info on
how the device works. Is the following the same thing?

http://adweb.desy.de/mdi/CARE/Lyon/Lyon%20DCCT_Technology_Review.pdf

(I googled second-harmonic DCCT)

George H.

Fig 3 is about right. The green feedback path is usually an N-turn
winding to net an N-to-1 current transformer.

There are usually two physical toroids. Ib, If, and T3 are wound on
both, as if they were a single core. T1 and T2 are each wound on one
of the cores, in opposite directions so that there's no net coupling
of the carrier frequency into T3 or the customer's Ib circuit.

The AC path (sense winding T3 and its amplifier, driving If) fight to
keep the flux zero at higher frequencies. The second-harmonic system
works at low frequencies, again to keep net core flux zero, which
happens when Ib = N * If.

I designed one of these once. It was fun, and not all that easy.

John

 

[daestrom]

Bill Sloman wrote:

On Nov 19, 3:18 pm, John Fields <jfie...@austininstruments.com> wrote:
On Wed, 18 Nov 2009 15:08:46 -0800 (PST),Bill Sloman





bill.slo...@ieee.org> wrote:
On Nov 18, 8:45 pm, John Fields <jfie...@austininstruments.com> wrote:
On Wed, 18 Nov 2009 08:46:00 -0800 (PST),Bill Sloman
bill.slo...@ieee.org> wrote:
On Nov 17, 9:28 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 17 Nov 2009 10:59:38 -0800, "Joel Koltner"
zapwireDASHgro...@yahoo.com> wrote:
"John Fields" <jfie...@austininstruments.com> wrote in message
news:sir5g5h9h69vfurapjd9e2kn8efeod8qat@4ax.com...
news:7ar5g59hdrcdpu3icb3rlmdn31iqiqfa67@4ax.com
5uA... nice!
Seems that someone on eBay is selling a +/-5uA movement:
http://cgi.ebay.com/Weston-Bakelite-Glass-5ua-microamp-Panel-Meter-Hi...
Nope, it'll get you nothing.
Know why?
Because the federales will toss your rear in jail quite rapidly?
---
Nope, because the magnetic field generated by the power line will never
cut the conductor wrapped around it since the conductor will be
essentially perpendicular to the varying field.
Since the original claim was
" >Wrapping some turns around the power company's lines will get you
many, many
watts. "
This isn't the reason - lines is plural and the nett current through
the lines as a bunch balances out to zero.
---
Since that's obvious to the most casual observer, the context of his
statement must have been about wrapping some turns around [one] of the
power company's lines, which I addressed by referring to it as "the
power line".
---
Nice try.
snipped the rest
---
Of course, you fraud, since by snipping the rest you sidestep the issue,
which is your ignorance in believing that a solenoid wound around an
alternating current carrying conductor can be used to extract power from
the varying magnetic field surrounding that conductor.

Your enthusiasm for inventing implausible straw men knows no bounds. I
never made any such claim. My scepticism about you claim was purely
based on the fact that you were ignoring what Joel Koltner had
actually said.

Nothing could be further from the truth, as demonstrated here:

news:26iag5hjpub42ookl0nk74vc3ffgs7316q@4ax.com

Since, conveniently, you don't have access to abse, I'll take the
liberty of emailing you the photos as soon as I post this.

Enjoy.

The pictures were perfectly clear. It was less obvious what you were
actually doing, but since I couldn't care less, this isn't any great
loss.

The joke is that even if you do extract "many watts" from the power
company's power lines, you won't be stealing from them. In order to be
able to extract power you have to be drawing power for which you will
be billed, and any extra watts you extract by transformer action is
subtracted from the power you are already paying for - your paid for
load will be seeing a lower drive voltage.

Joel Koltner made a rather good joke, which you have totally failed to
get.

If you make a 'tap' upstream of the revenue meter, even with just
transformer action, you're stealing. Revenue meters (kilowatt-hour
meters) have always had terminal voltage as one of their inputs. An
illegal tap upstream may affect the voltage at the service entrance some
small amount, but the metering will reduce the billed kWh accordingly.
So regardless of the exact voltage supplied by the utility (it often
varies slightly throughout the day), the amount of energy delivered at
the service entrance is what is billed for. Power drawn off before the
meter isn't measured and is 'stolen'.

Of course if you just 'wrap some turns around the power line' without
orienting the coil properly in relation to the line, you're not going to
get any power because transformer action won't work when your turns of
wire are parallel to the power line's magnetic field (i.e. 'wrapped
around' the power line). And I think that was John Field's point.

daestrom

 

[John Fields]

On Thu, 19 Nov 2009 10:43:58 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

On Nov 19, 3:18 pm, John Fields <jfie...@austininstruments.com> wrote:
On Wed, 18 Nov 2009 15:08:46 -0800 (PST),Bill Sloman





bill.slo...@ieee.org> wrote:
On Nov 18, 8:45 pm, John Fields <jfie...@austininstruments.com> wrote:
On Wed, 18 Nov 2009 08:46:00 -0800 (PST),Bill Sloman

bill.slo...@ieee.org> wrote:
On Nov 17, 9:28 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 17 Nov 2009 10:59:38 -0800, "Joel Koltner"

zapwireDASHgro...@yahoo.com> wrote:
"John Fields" <jfie...@austininstruments.com> wrote in message
news:sir5g5h9h69vfurapjd9e2kn8efeod8qat@4ax.com...
news:7ar5g59hdrcdpu3icb3rlmdn31iqiqfa67@4ax.com

5uA... nice!

Seems that someone on eBay is selling a +/-5uA movement:
http://cgi.ebay.com/Weston-Bakelite-Glass-5ua-microamp-Panel-Meter-Hi...

Nope, it'll get you nothing.
Know why?

Because the federales will toss your rear in jail quite rapidly?

---
Nope, because the magnetic field generated by the power line will never
cut the conductor wrapped around it since the conductor will be
essentially perpendicular to the varying field.

Since the original claim was

" >Wrapping some turns around the power company's lines will get you
many, many
watts. "

This isn't the reason - lines is plural and the nett current through
the lines as a bunch balances out to zero.

---
Since that's obvious to the most casual observer, the context of his
statement must have been about wrapping some turns around [one] of the
power company's lines, which I addressed by referring to it as "the
power line".
---

Nice try.

snipped the rest

---
Of course, you fraud, since by snipping the rest you sidestep the issue,
which is your ignorance in believing that a solenoid wound around an
alternating current carrying conductor can be used to extract power from
the varying magnetic field surrounding that conductor.

Your enthusiasm for inventing implausible straw men knows no bounds. I
never made any such claim. My scepticism about you claim was purely
based on the fact that you were ignoring what Joel Koltner had
actually said.

---
What Joel _actually_ said was that energy could be extracted from the
varying magnetic field surrounding a power line by wrapping turns around
it.

Since you pointed out that energy can't be had by wrapping turns around
bundled conductors carrying charge flowing in opposite directions,
that's something that, obviously, every dunce realizes.

Knowing that, my take on Koltner's lighthearted comment was that he was
referring to a single conductor, such as the ones used in high voltage
distribution systems which are called, by the way, "power lines".
---

Nothing could be further from the truth, as demonstrated here:

news:26iag5hjpub42ookl0nk74vc3ffgs7316q@4ax.com

Since, conveniently, you don't have access to abse, I'll take the
liberty of emailing you the photos as soon as I post this.

Enjoy.

The pictures were perfectly clear. It was less obvious what you were
actually doing, but since I couldn't care less, this isn't any great
loss.

---
You're really not much of an objective, honest, truth-seeking scientist,
are you?

If you're as smart as you unabashedly keep on proclaiming you are, you
should know very well what the pictures show; that energy cannot be
extracted from the varying magnetic field surrounding a conductor with a
solenoid-wound coil, but can be readily extracted using a
toroidally-wound coil.

Of course you have to feign ignorance and invoke indifference because
your position, from a technical point of view is untenable and you know
it, so in order to save face, instead of simply admitting error, you
resort to subterfuge.
---

The joke is that even if you do extract "many watts" from the power
company's power lines, you won't be stealing from them. In order to be
able to extract power you have to be drawing power for which you will
be billed, and any extra watts you extract by transformer action is
subtracted from the power you are already paying for - your paid for
load will be seeing a lower drive voltage.

---
Geez, Dr. Sloman, even for you that's pretty stupid.

Have you never even considered that getting "free" power involves
tapping into the lines on the energy company's side of the meter?
---

Joel Koltner made a rather good joke, which you have totally failed to
get.

---
Trying to make trouble, huh?

I have no quarrel with Joel and I don't think he has one with me since
all I did was apprise him, with no rancor, (with a little humor, even)
of the reason why one can't use a solenoid oriented coaxially with a
conductor carrying AC to extract energy from the varying field.

You, on the other hand, do nothing _but_ try to foment discord when your
errors are exposed, in an effort to diffuse the focus and allow you to
exit, without brickbats, from the melee you created in the first place.
JF

 

[John Fields]

On Thu, 19 Nov 2009 21:29:10 -0500, daestrom <daestrom@twcny.rr.com>
wrote:

If you make a 'tap' upstream of the revenue meter, even with just
transformer action, you're stealing. Revenue meters (kilowatt-hour
meters) have always had terminal voltage as one of their inputs. An
illegal tap upstream may affect the voltage at the service entrance some
small amount, but the metering will reduce the billed kWh accordingly.
So regardless of the exact voltage supplied by the utility (it often
varies slightly throughout the day), the amount of energy delivered at
the service entrance is what is billed for. Power drawn off before the
meter isn't measured and is 'stolen'.

Of course if you just 'wrap some turns around the power line' without
orienting the coil properly in relation to the line, you're not going to
get any power because transformer action won't work when your turns of
wire are parallel to the power line's magnetic field (i.e. 'wrapped
around' the power line). And I think that was John Field's point.

---
Indeed.

Thank you.

JF

 

[Tzortzakakis Dimitrios]

? "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> ?????? ???
?????? news:dnsag51jfmub8nppj2kfj3nt07l3jv6djg@4ax.com...

On Thu, 19 Nov 2009 07:29:26 -0800, Fester Bestertester <fbt@fbt.net
wrote:

So, for a millivolt output probe, this might be as simple as 2 windings
(or a
tapped single winding) with a range switch to select the winding?

Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.

Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.

Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.

http://en.wikipedia.org/wiki/Rogowski_coil

The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.

http://www.gmw.com/electric_current/Danfysik/866_867/867.html
Anyway, current transformers must always be operated with the secondary

shorted. In the generating facilities in Kozani, West Macedonia, where 400
kV current transformers were involved, the operators of the plant had a
special indicator whether the secondary was shorted.


--
Tzortzakakis Dimitrios
major in electrical engineering
mechanized infantry reservist
hordad AT otenet DOT gr

 

[daestrom]

Tzortzakakis Dimitrios wrote:

? "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> ?????? ???
?????? news:dnsag51jfmub8nppj2kfj3nt07l3jv6djg@4ax.com...
On Thu, 19 Nov 2009 07:29:26 -0800, Fester Bestertester <fbt@fbt.net
wrote:

So, for a millivolt output probe, this might be as simple as 2 windings
(or a
tapped single winding) with a range switch to select the winding?
Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.

Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.

Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.

http://en.wikipedia.org/wiki/Rogowski_coil

The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.

http://www.gmw.com/electric_current/Danfysik/866_867/867.html
Anyway, current transformers must always be operated with the secondary
shorted. In the generating facilities in Kozani, West Macedonia, where 400
kV current transformers were involved, the operators of the plant had a
special indicator whether the secondary was shorted.

Some old switchboard CT's I worked on in the Navy had very thin
insulator between two spring clips. Whenever we wanted to remove a
meter for cal, we slip the insulator out so the two clips would short
together, shorting the CT. Then we could open circuit the meter and
remove it from the panel. I don't remember exactly what the blade was
made of, but it's surface wasn't perfectly smooth like polished
material, more porous like unglazed ceramic (of course it wasn't any metal).

The reason they built the insulator so thin was that if one accidentally
open-circuited the CT without removing the wafer first, the high voltage
developed by the CT would just 'punch thru' the wafer and safely short
the CT. Then all you had to do to repair things was make sure you
closed the circuit and replace the wafer-thin insulator blade.

Was kind of surprised when I moved to commercial power systems that they
didn't use something similar. Just has to have a breakdown voltage that
is low enough to avoid damaging the CT.

daestrom

 

[John Larkin]

On Fri, 20 Nov 2009 10:53:45 -0500, daestrom <daestrom@twcny.rr.com>
wrote:

Tzortzakakis Dimitrios wrote:
? "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> ?????? ???
?????? news:dnsag51jfmub8nppj2kfj3nt07l3jv6djg@4ax.com...
On Thu, 19 Nov 2009 07:29:26 -0800, Fester Bestertester <fbt@fbt.net
wrote:

So, for a millivolt output probe, this might be as simple as 2 windings
(or a
tapped single winding) with a range switch to select the winding?
Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.

Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.

Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.

http://en.wikipedia.org/wiki/Rogowski_coil

The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.

http://www.gmw.com/electric_current/Danfysik/866_867/867.html
Anyway, current transformers must always be operated with the secondary
shorted. In the generating facilities in Kozani, West Macedonia, where 400
kV current transformers were involved, the operators of the plant had a
special indicator whether the secondary was shorted.


Some old switchboard CT's I worked on in the Navy had very thin
insulator between two spring clips. Whenever we wanted to remove a
meter for cal, we slip the insulator out so the two clips would short
together, shorting the CT. Then we could open circuit the meter and
remove it from the panel. I don't remember exactly what the blade was
made of, but it's surface wasn't perfectly smooth like polished
material, more porous like unglazed ceramic (of course it wasn't any metal).

The reason they built the insulator so thin was that if one accidentally
open-circuited the CT without removing the wafer first, the high voltage
developed by the CT would just 'punch thru' the wafer and safely short
the CT. Then all you had to do to repair things was make sure you
closed the circuit and replace the wafer-thin insulator blade.

Was kind of surprised when I moved to commercial power systems that they
didn't use something similar. Just has to have a breakdown voltage that
is low enough to avoid damaging the CT.

daestrom

Lower-power CT, like residential-metering size, 100 amps or so, will
generally tolerate being unloaded. They will saturate and make two
not-too-huge voltage spikes per cycle and not get very warm. The nasty
part is that, once the burden is reconnected, they are very likely to
wind up magnetized, which will mess up low-current accuracy.

John

 

[JosephKK]

On Tue, 17 Nov 2009 07:20:32 -0800 (PST), Tim Williams
<tmoranwms@gmail.com> wrote:

On Nov 17, 2:18 am, Fester Bestertester <f...@fbt.net> wrote:
I'm curious how the Fluke i200s current clamp probe can give mV output
without the use of batteries.

Is that the one with the 10/100 switch and a green LED?

I'm pretty sure most of the weight is not ferrite, it's a battery
somewhere.

Actually about equally ferrite and plastic with copper coming at about
1/3 either of those. No battery whatsoever and AC only.

They also read DC, and have an offset knob to account for the
ferrite's hysteresis.

Only active probes do that.

The passive probes only read AC, and as I recall, are 1 or 10 mV/A.

Tim

I can make any output ratio i want, i know how they work.

 

[Bill Sloman]

On Nov 20, 1:31 pm, John Fields <jfie...@austininstruments.com> wrote:

On Thu, 19 Nov 2009 10:43:58 -0800 (PST),Bill Sloman





bill.slo...@ieee.org> wrote:
On Nov 19, 3:18 pm, John Fields <jfie...@austininstruments.com> wrote:
On Wed, 18 Nov 2009 15:08:46 -0800 (PST),Bill Sloman

bill.slo...@ieee.org> wrote:
On Nov 18, 8:45 pm, John Fields <jfie...@austininstruments.com> wrote:
On Wed, 18 Nov 2009 08:46:00 -0800 (PST),Bill Sloman

bill.slo...@ieee.org> wrote:
On Nov 17, 9:28 pm, John Fields <jfie...@austininstruments.com> wrote:
On Tue, 17 Nov 2009 10:59:38 -0800, "Joel Koltner"

zapwireDASHgro...@yahoo.com> wrote:
"John Fields" <jfie...@austininstruments.com> wrote in message
news:sir5g5h9h69vfurapjd9e2kn8efeod8qat@4ax.com...
news:7ar5g59hdrcdpu3icb3rlmdn31iqiqfa67@4ax.com

5uA... nice!

Seems that someone on eBay is selling a +/-5uA movement:
http://cgi.ebay.com/Weston-Bakelite-Glass-5ua-microamp-Panel-Meter-Hi...

Nope, it'll get you nothing.
Know why?

Because the federales will toss your rear in jail quite rapidly?

---
Nope, because the magnetic field generated by the power line will never
cut the conductor wrapped around it since the conductor will be
essentially perpendicular to the varying field.

Since the original claim was

" >Wrapping some turns around the power company's lines will get you
many, many
watts. "

This isn't the reason - lines is plural and the nett current through
the lines as a bunch balances out to zero.

---
Since that's obvious to the most casual observer, the context of his
statement must have been about wrapping some turns around [one] of the
power company's lines, which I addressed by referring to it as "the
power line".
---

Nice try.

snipped the rest

---
Of course, you fraud, since by snipping the rest you sidestep the issue,
which is your ignorance in believing that a solenoid wound around an
alternating current carrying conductor can be used to extract power from
the varying magnetic field surrounding that conductor.

Your enthusiasm for inventing implausible straw men knows no bounds. I
never made any such claim. My scepticism about you claim was purely
based on the fact that you were ignoring what Joel Koltner had
actually said.

---
What Joel _actually_ said was that energy could be extracted from the
varying magnetic field surrounding a power line by wrapping turns around
it.

Since you pointed out that energy can't be had by wrapping turns around
bundled conductors carrying charge flowing in opposite directions,
that's something that, obviously, every dunce realizes.

Knowing that, my take on Koltner's lighthearted comment was that he was
referring to a single conductor, such as the ones used in high voltage
distribution systems which are called, by the way, "power lines".

Wrapping turns around a high voltage power line probably wouldn't be a
good idea.

<snip>

--
Bill Sloman, Nijmegen

 

[John Fields]

On Fri, 20 Nov 2009 10:43:14 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

On Nov 20, 1:31 pm, John Fields <jfie...@austininstruments.com> wrote:

What Joel _actually_ said was that energy could be extracted from the
varying magnetic field surrounding a power line by wrapping turns around
it.

Since you pointed out that energy can't be had by wrapping turns around
bundled conductors carrying charge flowing in opposite directions,
that's something that, obviously, every dunce realizes.

Knowing that, my take on Koltner's lighthearted comment was that he was
referring to a single conductor, such as the ones used in high voltage
distribution systems which are called, by the way, "power lines".

Wrapping turns around a high voltage power line probably wouldn't be a
good idea.

---
So, then, you agree that, aside from the obvious danger of wrapping
turns around a high voltage line, no appreciable power can be drawn from
the line by a coaxial solenoid surrounding the line?

JF

 

[JosephKK]

On Fri, 20 Nov 2009 08:44:19 -0800, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 20 Nov 2009 10:53:45 -0500, daestrom <daestrom@twcny.rr.com
wrote:

Tzortzakakis Dimitrios wrote:
? "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> ?????? ???
?????? news:dnsag51jfmub8nppj2kfj3nt07l3jv6djg@4ax.com...
On Thu, 19 Nov 2009 07:29:26 -0800, Fester Bestertester <fbt@fbt.net
wrote:

So, for a millivolt output probe, this might be as simple as 2 windings
(or a
tapped single winding) with a range switch to select the winding?
Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.

Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.

Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.

http://en.wikipedia.org/wiki/Rogowski_coil

The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.

http://www.gmw.com/electric_current/Danfysik/866_867/867.html
Anyway, current transformers must always be operated with the secondary
shorted. In the generating facilities in Kozani, West Macedonia, where 400
kV current transformers were involved, the operators of the plant had a
special indicator whether the secondary was shorted.


Some old switchboard CT's I worked on in the Navy had very thin
insulator between two spring clips. Whenever we wanted to remove a
meter for cal, we slip the insulator out so the two clips would short
together, shorting the CT. Then we could open circuit the meter and
remove it from the panel. I don't remember exactly what the blade was
made of, but it's surface wasn't perfectly smooth like polished
material, more porous like unglazed ceramic (of course it wasn't any metal).

The reason they built the insulator so thin was that if one accidentally
open-circuited the CT without removing the wafer first, the high voltage
developed by the CT would just 'punch thru' the wafer and safely short
the CT. Then all you had to do to repair things was make sure you
closed the circuit and replace the wafer-thin insulator blade.

Was kind of surprised when I moved to commercial power systems that they
didn't use something similar. Just has to have a breakdown voltage that
is low enough to avoid damaging the CT.

daestrom

Lower-power CT, like residential-metering size, 100 amps or so, will
generally tolerate being unloaded. They will saturate and make two
not-too-huge voltage spikes per cycle and not get very warm. The nasty
part is that, once the burden is reconnected, they are very likely to
wind up magnetized, which will mess up low-current accuracy.

John

There is no CT in residential metering, the energy meter is connected
directly. Even commercial / light industrial you do not see CTs in
the meter circuit until 600 A, and before that you are typically at
480 V 3-phase (in the US).

 

[John Larkin]

On Sat, 21 Nov 2009 04:29:36 -0800,
"JosephKK"<quiettechblue@yahoo.com> wrote:

On Fri, 20 Nov 2009 08:44:19 -0800, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Fri, 20 Nov 2009 10:53:45 -0500, daestrom <daestrom@twcny.rr.com
wrote:

Tzortzakakis Dimitrios wrote:
? "John Larkin" <jjlarkin@highNOTlandTHIStechnologyPART.com> ?????? ???
?????? news:dnsag51jfmub8nppj2kfj3nt07l3jv6djg@4ax.com...
On Thu, 19 Nov 2009 07:29:26 -0800, Fester Bestertester <fbt@fbt.net
wrote:

So, for a millivolt output probe, this might be as simple as 2 windings
(or a
tapped single winding) with a range switch to select the winding?
Current transformers are usually dumped into a load resistor aka
burden resistor, to convert their output current into voltage. I'm
sure the Fluke clamp-on has an internal burden resistor, and they may
switch that to change ranges.

Without a burden resistor, the output voltage will be proportional to
frequency and very dependent on core reluctance, which would be fatal
for a clamp-on meter with a hinge and a non-repeatable air gap.

Coreless Rogowsky coils are used unloaded, but need a downstream
integrator to accurately measure current.

http://en.wikipedia.org/wiki/Rogowski_coil

The coolest current transformer is a second-harmonic DCCT, accurate to
parts-per-million from DC to many kilohertz.

http://www.gmw.com/electric_current/Danfysik/866_867/867.html
Anyway, current transformers must always be operated with the secondary
shorted. In the generating facilities in Kozani, West Macedonia, where 400
kV current transformers were involved, the operators of the plant had a
special indicator whether the secondary was shorted.


Some old switchboard CT's I worked on in the Navy had very thin
insulator between two spring clips. Whenever we wanted to remove a
meter for cal, we slip the insulator out so the two clips would short
together, shorting the CT. Then we could open circuit the meter and
remove it from the panel. I don't remember exactly what the blade was
made of, but it's surface wasn't perfectly smooth like polished
material, more porous like unglazed ceramic (of course it wasn't any metal).

The reason they built the insulator so thin was that if one accidentally
open-circuited the CT without removing the wafer first, the high voltage
developed by the CT would just 'punch thru' the wafer and safely short
the CT. Then all you had to do to repair things was make sure you
closed the circuit and replace the wafer-thin insulator blade.

Was kind of surprised when I moved to commercial power systems that they
didn't use something similar. Just has to have a breakdown voltage that
is low enough to avoid damaging the CT.

daestrom

Lower-power CT, like residential-metering size, 100 amps or so, will
generally tolerate being unloaded. They will saturate and make two
not-too-huge voltage spikes per cycle and not get very warm. The nasty
part is that, once the burden is reconnected, they are very likely to
wind up magnetized, which will mess up low-current accuracy.

John

There is no CT in residential metering, the energy meter is connected
directly. Even commercial / light industrial you do not see CTs in
the meter circuit until 600 A, and before that you are typically at
480 V 3-phase (in the US).

Of course there is. I delivered over 1800 electronic submetering units
for the Battery Park City apartment complex, and, trust me, we used
CTs. Lots of electronic meters use CTs. You should get out more.

John

 

[James Sweet]

There is no CT in residential metering, the energy meter is connected
directly. Even commercial / light industrial you do not see CTs in
the meter circuit until 600 A, and before that you are typically at
480 V 3-phase (in the US).

My uncle's house (in the US) has a 400A service with current
transformers. They're not common but they do exist. IIRC 200A is the
largest residential meter.

 

[John Larkin]

On Sat, 21 Nov 2009 12:37:10 -0800, James Sweet
<jamesrsweet@gmail.com> wrote:

There is no CT in residential metering, the energy meter is connected
directly. Even commercial / light industrial you do not see CTs in
the meter circuit until 600 A, and before that you are typically at
480 V 3-phase (in the US).


My uncle's house (in the US) has a 400A service with current
transformers. They're not common but they do exist. IIRC 200A is the
largest residential meter.

It's dangerous to make catagorical statements like "There is no CT in
residential metering." It only takes one counter-case to make you
wrong.

John

 

[Michael A. Terrell]

John Larkin wrote:

On Sat, 21 Nov 2009 12:37:10 -0800, James Sweet
jamesrsweet@gmail.com> wrote:



There is no CT in residential metering, the energy meter is connected
directly. Even commercial / light industrial you do not see CTs in
the meter circuit until 600 A, and before that you are typically at
480 V 3-phase (in the US).


My uncle's house (in the US) has a 400A service with current
transformers. They're not common but they do exist. IIRC 200A is the
largest residential meter.

It's dangerous to make catagorical statements like "There is no CT in
residential metering." It only takes one counter-case to make you
wrong.

Like the claim that no US homes have three phase power that was made
on this group (alt.engineering.electrical) a few years ago.


--
The movie 'Deliverance' isn't a documentary!

 

[John Fields]

On Fri, 20 Nov 2009 10:43:14 -0800 (PST), Bill Sloman
<bill.sloman@ieee.org> wrote:

On Nov 20, 1:31 pm, John Fields <jfie...@austininstruments.com> wrote:

Knowing that, my take on Koltner's lighthearted comment was that he was
referring to a single conductor, such as the ones used in high voltage
distribution systems which are called, by the way, "power lines".

Wrapping turns around a high voltage power line probably wouldn't be a
good idea.

---
He said, with his last breath, and then quietly sank into the sea...

JF