Non-contact Voltage/Current Measurement

[Preppy]

Hi everyone,

I'm wondering about plausible methods which could be used to accurately
sense voltages and currents from high tension overhead AC power lines.
Aside from the conventional potential and current transformers, I'm
thinking about ways of doing measurements without contact with the
cables and perhaps from a distance from cable, by observing E and M
fields around the cable, for example. I know of one technique
involving the measurement of the effects of E and H fields on light
around the conductor, where optical fiber is used (the Farady effect,
and Pockels effect).

Anyone think of other methods? Is it possible to use lasers from a
distance? Or, some sort of ELF field measurement?

Thanks for your thoughts - been curious about this for a while.

Paul

 

[Uncle Al]

Hi everyone,

I'm wondering about plausible methods which could be used to accurately
sense voltages and currents from high tension overhead AC power lines.
Aside from the conventional potential and current transformers, I'm
thinking about ways of doing measurements without contact with the
cables and perhaps from a distance from cable, by observing E and M
fields around the cable, for example. I know of one technique
involving the measurement of the effects of E and H fields on light
around the conductor, where optical fiber is used (the Farady effect,
and Pockels effect).

Anyone think of other methods? Is it possible to use lasers from a
distance? Or, some sort of ELF field measurement?

For one isolated power line the electric field will vary inversely
with distance (not distance squared). An AC line will allow
phase-lock detection. Maybe Zeemann and Stark splittings of emissions
at a focused mid-air laser pulse for the magnetic and electric fields
respectively.

High voltage lines are immensely dangerous You won't find any birds
perched on them. Linemen wear steel mesh Faraday cage clothing in
addition to clamping on.

 

[Henry Kolesnik]

Uncle Al

Birds do sit on million volt lines and in Brazil and China maintenace
workers have a safe system to get on these lines and they work on them live
with over a million volts and live. LADP tried in vain to get permission to
maintain their million volt line from Utah to LA but regualtory dummies
couldn't understand technology and denied permisssion.

73
Hank WD5JFR

 

[John Woodgate]

I read in sci.electronics.design that Preppy <[email protected]>

I'm wondering about plausible methods which could be used to accurately
sense voltages and currents from high tension overhead AC power lines.
Aside from the conventional potential and current transformers, I'm
thinking about ways of doing measurements without contact with the
cables and perhaps from a distance from cable, by observing E and M
fields around the cable, for example. I know of one technique involving
the measurement of the effects of E and H fields on light around the
conductor, where optical fiber is used (the Farady effect, and Pockels
effect).

Anyone think of other methods? Is it possible to use lasers from a
distance? Or, some sort of ELF field measurement?

You don't need to use complicated means like Faraday and Pockels;
conventional electronics techniques are much simpler, far more sensitive
and quite accurate enough for any purpose you are likely to have.

Measurement of magnetic field is easy; in principle all you need is a
pickup coil (small inductor on a *bobbin-type* ferrite core) and a
suitable amplifier. Calibration isn't difficult, either; a single-turn
coil produces a calculable field strength at low frequencies.

Electric field measurements are a little more tricky to get working, but
basically you just have a well-insulated electrode connected to a high-
impedance buffer amplifier, whose other input terminal is earthed.

 

[Preppy]

I read in sci.electronics.design that Preppy <[email protected]>


You don't need to use complicated means like Faraday and Pockels;
conventional electronics techniques are much simpler, far more
sensitive and quite accurate enough for any purpose you are likely to
have.

Measurement of magnetic field is easy; in principle all you need is a
pickup coil (small inductor on a *bobbin-type* ferrite core) and a
suitable amplifier. Calibration isn't difficult, either; a single-turn
coil produces a calculable field strength at low frequencies.

Electric field measurements are a little more tricky to get working,
but basically you just have a well-insulated electrode connected to a
high- impedance buffer amplifier, whose other input terminal is
earthed.

Thanks for the comments John. I have a few questions about your
thoughts. If we are using field measurements to determine voltage and
current, wouldn't one have to eliminate the effects from adjacent
conductors? You would think that the geometry of the lines and their
location relative to your measurment would have a major impact and be
very hard to get right. Then there is the issue of calibration, of
course . . . if we wanted accurate readings (less than 1% lets say).

Thanks,

Paul

 

[John Woodgate]

I read in sci.electronics.design that Preppy <[email protected]>

I have a few questions about your
thoughts. If we are using field measurements to determine voltage and
current,

Is that what you are trying to do? Your question said 'sense', so I
thought you were more concerned with the fields produced than the actual
voltages and currents.

You can determine the voltages and currents by asking the distribution
company. But they may want to know why you want to know!

 

[Preppy]

I read in sci.electronics.design that Preppy <[email protected]>


Is that what you are trying to do? Your question said 'sense', so I
thought you were more concerned with the fields produced than the actual
voltages and currents.

Yes, trying to actually measure voltages and currents - presumably by
observing near fields.

You can determine the voltages and currents by asking the distribution
company. But they may want to know why you want to know!

Of course, but let's say I AM the distribution company , and I want
to do measurements for diagnostics reasons. I'm trying to determine if
the physics involved are feasible. I stand on the ground, and point my
ELF antenna at the lines, and measure voltage current. Easier said than
done, but I wonder if it can be done.

Tnks

Paul

 

[John Woodgate]

I read in sci.electronics.design that Preppy <[email protected]>

I stand on the ground, and point my
ELF antenna at the lines, and measure voltage current. Easier said than
done, but I wonder if it can be done.

AFAIK, instruments to do this are commercially available, but costly.

 

[Paul W.]

I read in sci.electronics.design that Preppy <[email protected]>


AFAIK, instruments to do this are commercially available, but costly.

I see. Any idea who and what they are called?

Paul

 

[Paul Hovnanian P.E.]

I see. Any idea who and what they are called?

Current transformers and potential transformers. Typically, these are
installed at fixed points along high voltage transmission systems, at
substations. There isn't much need for portable equipment. By that, I
mean remote sensing equipment that can be temporarily attached to the
line. Its pretty easy to diagnose line problems by making measurements
from either end since there aren't any lateral taps between substations.

On distribution lines (around 12 to 34kV), there are clamp-on current
transformers that can be installed to monitor load distribution on
lateral lines, etc.

 

[Franz Heymann]

I read in sci.electronics.design that Preppy <[email protected]>


You don't need to use complicated means like Faraday and Pockels;
conventional electronics techniques are much simpler, far more sensitive
and quite accurate enough for any purpose you are likely to have.

Measurement of magnetic field is easy; in principle all you need is a
pickup coil (small inductor on a *bobbin-type* ferrite core) and a
suitable amplifier. Calibration isn't difficult, either; a single-turn
coil produces a calculable field strength at low frequencies.

Electric field measurements are a little more tricky to get working, but
basically you just have a well-insulated electrode connected to a high-
impedance buffer amplifier, whose other input terminal is earthed.

How do you cope with the fact that the presence of the probe and its lead to
the amplifier lays hell out of the field distribution which you are trying
to measure?

Franz

 

[JeffM]

voltage measurements without contact with the cables
http://www.google.com/search?num=10...meters+"without+*+contact"&btnG=Google+Search

 

[Uncle Al]

How do you cope with the fact that the presence of the probe and its lead to
the amplifier lays hell out of the field distribution which you are trying
to measure?

I agree. It must be a dielectric probe (fiberoptic) or
well-collimated EMF. Getting within 15 feet of a high-voltage line
can be suicide. An inert remote probe looks to be the OP's question.
All that gives you to work with is air and fields (and maybe the glass
or porcelain of the insulators). The probe would nominally be a laser
beam. The only things I can imagine that would rise above background
- and then preferably at night - would be phase-locked detection of
Stark (electric) and Zeeman (magnetic) splittings of atomic and
molecular transitions. You might have to pop a laser focus in situ to
get emitting species.

 

[Preppy]

I agree. It must be a dielectric probe (fiberoptic) or
well-collimated EMF. Getting within 15 feet of a high-voltage line
can be suicide. An inert remote probe looks to be the OP's question.
All that gives you to work with is air and fields (and maybe the glass
or porcelain of the insulators). The probe would nominally be a laser
beam. The only things I can imagine that would rise above background
- and then preferably at night - would be phase-locked detection of
Stark (electric) and Zeeman (magnetic) splittings of atomic and
molecular transitions. You might have to pop a laser focus in situ to
get emitting species.

Sounds like a bucket of fun. What about just a cleverly designed ELF
antenna designed and positioned with good symmetry well away from the
lines at a safe distance? Those near-fields should be pretty strong
when dealing with high tension lines.

How would one measure the splittings from the laser?

Paul

 

[Uncle Al]

[snip]

I agree. It must be a dielectric probe (fiberoptic) or
well-collimated EMF. Getting within 15 feet of a high-voltage line
can be suicide. An inert remote probe looks to be the OP's question.
All that gives you to work with is air and fields (and maybe the glass
or porcelain of the insulators). The probe would nominally be a laser
beam. The only things I can imagine that would rise above background
- and then preferably at night - would be phase-locked detection of
Stark (electric) and Zeeman (magnetic) splittings of atomic and
molecular transitions. You might have to pop a laser focus in situ to
get emitting species.

Sounds like a bucket of fun. What about just a cleverly designed ELF
antenna designed and positioned with good symmetry well away from the
lines at a safe distance? Those near-fields should be pretty strong
when dealing with high tension lines.

How would one measure the splittings from the laser?

In one version the scanned laser or maser would interrogate or pump
existing molecular transitions. In another, a pulsed laser focus
would excite a small volume of air and the UV-Vis-NIR emissions would
be subject to high-finesse spectroscopy. Good for studies, not nearly
so good for real world data.

 

[Thomas C. Sefranek]

Uncle Al

Birds do sit on million volt lines

Not in this life! Look a bit closer!
They sit on the ground lines used for lightning conductors.
The high tension lines irritate them well before alighting on the wire.

and in Brazil and China maintenace
workers have a safe system to get on these lines and they work on them live
with over a million volts and live. LADP tried in vain to get permission to
maintain their million volt line from Utah to LA but regualtory dummies
couldn't understand technology and denied permisssion.

Yea, it's hard to get the word out.


--
*
| __O Thomas C. Sefranek [email protected]
|_-\<,_ Amateur Radio Operator: WA1RHP
(*)/ (*) Bicycle mobile on 145.41, 448.625 MHz

http://hamradio.cmcorp.com/inventory/Inventory.html
http://www.harvardrepeater.org

 

[Isaac Wingfield]

Sounds like a bucket of fun. What about just a cleverly designed ELF
antenna designed and positioned with good symmetry well away from the
lines at a safe distance? Those near-fields should be pretty strong
when dealing with high tension lines.

The near fields (either E or M) vary as the fourth power of distance.
Calibration is left as an exercise for the student.

Isaac

 

[Uncle Al]

Not in this life! Look a bit closer!
They sit on the ground lines used for lightning conductors.
The high tension lines irritate them well before alighting on the wire.

Yea, it's hard to get the word out.

The bird quote is not mine. Definitely, and exactly the opposite.
Any bird coming toward a 500K transmission line would be fried in
mid-air. Workers clamp onto 100 kV lines routinely - including
helicopter-based maintenance. The really high tension stuff requires
wearing a personal Faraday cage - steel mesh suit in canvas - or you
get fried by the field even though you are clamped on. It takes big
balls in a chainmail sack to be a lineman.

 

[Franz Heymann]

The near fields (either E or M) vary as the fourth power of distance.
Calibration is left as an exercise for the student.

No. 1/r^2 approximately.

Franz

 

[Mark Folsom]

I agree. It must be a dielectric probe (fiberoptic) or
well-collimated EMF. Getting within 15 feet of a high-voltage line
can be suicide. An inert remote probe looks to be the OP's question.
All that gives you to work with is air and fields (and maybe the glass
or porcelain of the insulators). The probe would nominally be a laser
beam. The only things I can imagine that would rise above background
- and then preferably at night - would be phase-locked detection of
Stark (electric) and Zeeman (magnetic) splittings of atomic and
molecular transitions. You might have to pop a laser focus in situ to
get emitting species.

Use a piezoelectric wafer and measure the thickness of it optically.

Mark Folsom