Experiments

Status
Not open for further replies.
SG-1 said:
If you have any of Ben Franklins DNA you might want to stroll around during a thunderstorm with your new Fluorescent tube handled umbrella & see how that lights up your path.
Click to expand...
"I don't think so, Tim!" ~ Al Boreland
 
Here's an interesting idea. A whole bunch of people (a lot of them) standing under HV lines will in fact change the impedance of the lines. Why? Because the human body has less electrical resistance than air does, thus the leakage current now has less ohms between lines and ground ;)

You can also take a whole bunch of rebar, glue a part of their end into pvc, jam the pvc into the ground, place a whole bunch of them between two towers (which can be 100yds or more), rebar stands 5-6ft in the air. Now connect all the bottoms of rebar together with wire (bond them just above the pvc, above the gnd, etc) and then take a wire from the last rebar and connect a load between it and the earth (or metal of a tower). Power away folks, power away.

Ever wonder what happens to the line impedance when it rains? HV perhaps saves more from low amps but also has some challenges dealing with leakage and impedance fluctuations.

Wrapping the lines in say a pvc sheath would help the poco, but that's extra cost and weight.
 
FionaZuppa said:
Here's an interesting idea. A whole bunch of people (a lot of them) standing under HV lines will in fact change the impedance of the lines. Why? Because the human body has less electrical resistance than air does, thus the leakage current now has less ohms between lines and ground ;)

You can also take a whole bunch of rebar, glue a part of their end into pvc, jam the pvc into the ground, place a whole bunch of them between two towers (which can be 100yds or more), rebar stands 5-6ft in the air. Now connect all the bottoms of rebar together with wire (bond them just above the pvc, above the gnd, etc) and then take a wire from the last rebar and connect a load between it and the earth (or metal of a tower). Power away folks, power away.

Ever wonder what happens to the line impedance when it rains? HV perhaps saves more from low amps but also has some challenges dealing with leakage and impedance fluctuations.

Wrapping the lines in say a pvc sheath would help the poco, but that's extra cost and weight.
Click to expand...

I don't think that's correct. As gar has pointed out, there is no leakage current with pure capacitive coupling. You need something that is actually putting a load on the system to get current flow.
 
LarryFine said:
According to my EE friend, damp air has greater impedance (higher dielectric strength) than dry air, not less.
Click to expand...

In my last house I had a plug-in fluorescent fixture over a very small workbench. As there was apparently no vapor barrier under the sort-of concrete floor, it was perpetually damp in the warmer months. During such times, I would have to touch the lamps in order to get them to fire up.
 
LarryFine said:
According to my EE friend, damp air has greater impedance (higher dielectric strength) than dry air, not less.
Click to expand...

I suspect not. Here's a real world example to explain it.

Data centers do not allow humidity to drop too low,,, why? Because when the air is dry it allows static charge to build up on objects. Having moisture in the air provides more "conductor" and less "insulator", thus no static charge buildup. In other words, there's more free electrons available with water in the air. Remember, when water (not steam) is in the air its usually not 100% pure water, etc.

gadfly56 said:
I don't think that's correct. As gar has pointed out, there is no leakage current with pure capacitive coupling. You need something that is actually putting a load on the system to get current flow.
Click to expand...
Things sticking up under HV lines are not ideal caps. And, its alternating field at 60Hz, and we know caps "pass" current in alternating e field. A cap is physically an open circuit, but will appear to pass current when its subject to e field that has Hz, etc. All caps have leakage even when placed in a vacuum.
 
Last edited:
LarryFine said:
According to my EE friend, damp air has greater impedance (higher dielectric strength) than dry air, not less.
Click to expand...

I suspect that either he was mistaken or you misunderstood him. A vacuum has the highest dielectric strength.
 
I think GAR was speaking of conduction current, no electron flow.

If you wire a light bulb in series with a capacitor it burns just fine. Yet no electrons pass through the capacitor. The electric current through the capacitor is displacement current, no charge flow.
 
190111-2127 EST

An ideal capacitor dissipates no energy as heat when an AC current flows thru the capacitor.

Generally when leakage is used with the discussion of a capacitor it refers to resistive components of the capacitor that dissipates heat as current flows thru the capacitor.

With respect to power lines there is power lost via objects in the electric and magnetic fields of the power lines. There is also radio frequency radiation at 60 Hz from the power lines, but not much.

When a new object is placed in the fields of the power lines it places an additional loss load on the power system. The object might reduce some other losses, but it does not totally replace other losses, and therefore it is a new net load on the power system.

.
 
LarryFine said:
According to my EE friend, damp air has greater impedance (higher dielectric strength) than dry air, not less.
Click to expand...

My research into this indicates that water vapor has a higher Voltage Break Down than dry air. Ions are recombined into the water droplets before they can form into an electric circuit.

The presence of water on the contaminated surface of insulators & other materials does make a flashover more likely in the presence of corona discharge.
 
SG-1 said:
My research into this indicates that water vapor has a higher Voltage Break Down than dry air. Ions are recombined into the water droplets before they can form into an electric circuit.

The presence of water on the contaminated surface of insulators & other materials does make a flashover more likely in the presence of corona discharge.
Click to expand...

dry air is more of an insulator than humid air
humid air is more of a conductor than dry air

https://www.physicsclassroom.com/class/estatics/Lesson-1/Conductors-and-Insulators


Pure H2O is a good insulator, and if you displace air molecules with pure H2O the mixture moves towards better insulator. Outside of special lab tests and environment (aka "real world"), the higher %RH the easier it is for charge to migrate, hence a better conductor.
 
190112-0923 EST

Distilled water exposed to air has moderately low conductivity, but nothing close to ultra pure water.

Several sources indicate that distilled water exposed to air has a resistivity of about 1 megohm-cm. Measurements I have made with grocery store distilled water might imply somewhat lower. Rain or fresh snow water is quite a bit lower than store distilled water, but not nearly as low as tap water. Note there is a 100 to 1 ratio difference between megohm-cm and megohm-meter.

Several references:

https://www.google.com/search?q=ohm....69i57j0l4.30126j0j8&sourceid=chrome&ie=UTF-8

https://www.researchgate.net/post/W...distilled_water_and_deionized_water_DI_water2

https://www.labmanager.com/white-pa...ty-measurement-of-purified-water#.XDoAXyMrLAw

.
 
On the other hand:

E. Miscellaneous correction factors. Changes in the air medium that forms the insulation influences the strength of an air gap. A brief discussion of each factor follows.


1. Dielectric strength of air. The dielectric strength of air in a uniform electric field at standard atmospheric conditions is approximately 3 kilovolts per millimeter.


The pressure, temperature, and humidity of the air, the shape, dimensions, and separation of the electrodes, and the characteristics of the applied voltage (wave shape) affect the disruptive gradient.


2. Atmospheric effect. The empirically determined electrical strength of a given gap is normally applicable at standard atmospheric conditions (20 °C, 101.3 kilopascals, 11 grams/cubic centimeter humidity). An increase in the density (humidity) of the air inhibits sparkover for a given air gap. The combination of temperature and air pressure that results in the lowest gap sparkover voltage is high temperature and low pressure. This combination of conditions is not likely to occur. Low air pressure, generally associated with high humidity, causes increased electrical strength. An average air pressure generally correlates with low humidity. Hot and dry working conditions normally result in reduced electrical strength. The equations for minimum approach distances in Table R-3 assume standard atmospheric conditions.


3. Altitude. The reduced air pressure at high altitudes causes a reduction in the electrical strength of an air gap. An employer must increase the minimum approach distance by about 3 percent per 300 meters (1,000 feet) of increased altitude for altitudes above 900 meters (3,000 feet). Table R-5 specifies the altitude correction factor that the employer must use in calculating minimum approach distances.



Source: https://www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.269AppB
 
190112-1341 EST

Circuit breakers, such as those made by Mechanical Products, for aircraft use have to be tested under low pressure conditions.

In the early 1960s I did some consulting work at MP. One project was to solve a production problem on an order for the breakers for the prototype B-1 bomber. Yield was initially only about 5% because of the very tight specifications. Finding the problem I was able to improve the yield to about 95%.

At the time I did work at MP it was family owned by Mr. Knapp, and his son in law Lyle Trolz was president. I liked brownies, and when we went to lunch Mr. Knapp always made sure I had brownies for dessert. In the early 1960s MP was sold to Howard Aiken, and that is how I met him. Aiken was the driving force behind the Harvard Mark I. Approximately 1935 Aiken proposed the idea of a digital computer, but his idea received no support at that time. James B. Conant was president of Harvard at that time. Thru a Harvard VP Aiken was put in contact with IBM and that got the Mark I started.

https://en.wikipedia.org/wiki/Harvard_Mark_I
https://en.wikipedia.org/wiki/James_B._Conant

.
 
LarryFine said:
2. Atmospheric effect. The empirically determined electrical strength of a given gap is normally applicable at standard atmospheric conditions (20 °C, 101.3 kilopascals, 11 grams/cubic centimeter humidity). An increase in the density (humidity) of the air inhibits sparkover for a given air gap. The combination of temperature and air pressure that results in the lowest gap sparkover voltage is high temperature and low pressure. This combination of conditions is not likely to occur. Low air pressure, generally associated with high humidity, causes increased electrical strength. An average air pressure generally correlates with low humidity. Hot and dry working conditions normally result in reduced electrical strength. The equations for minimum approach distances in Table R-3 assume standard atmospheric conditions.
Click to expand...
Where does the term "electrical strength" come from? We describe items in terms of resistance (R), or conductance (1/R).

Dry add is a better conductor?? Seems to be contradictory.

Static electricity is caused by an imbalance of electrons on a surface. Atoms normally contain an equal number of protons (positively charged particles) and electrons (negatively charged packets of energy). When they don't, the result can be shocking. Why? Because when two materials in motion make contact, electrons jump from one to the other to fix the imbalance!
So what do temperature and humidity have to do with static electricity? Moisture makes the air more conductive, so it can absorb and more evenly distribute excess charges. On humid (wet) days, objects don’t hold static charges quite as well. Also, temperature changes can generate a temporary voltage. This is known as the pyroelectric effect.

Author: Judee Shipman
Click to expand...

Ref: https://www.education.com/science-fair/article/temperature-humidity-static-charges-last/

Perhaps when looking at leakage from HV lines, the flash voltage # is not as important as the conductivity of the air. That is, if I believe you get higher flash V # when the air is less %RH.
 
FionaZuppa said:
Where does the term "electrical strength" come from? We describe items in terms of resistance (R), or conductance (1/R).

Dry add is a better conductor?? Seems to be contradictory.



Ref: https://www.education.com/science-fair/article/temperature-humidity-static-charges-last/

Perhaps when looking at leakage from HV lines, the flash voltage # is not as important as the conductivity of the air. That is, if I believe you get higher flash V # when the air is less %RH.
Click to expand...
Electric strength is measured in volts per meter and is purely a measure of breakdown voltage characteristics. It can be measured from one side of a solid insulator to the other or from point to point in dry air. It can also be measured from point to point along the surface of an interface between two insulators, such as ceramic and air.
Electric strength can be measured between two (approximately) infinite parallel plates to avoid the complication of electric field gradients. A point or small radius of curvature can make breakdown easier because the electric field is stronger close to the point

Sent from my XT1585 using Tapatalk
 
LarryFine said:
An increase in the density (humidity) of the air ... Low air pressure, generally associated with high humidity,
Click to expand...


Something doesn't seem to fit. Above is self contradictory?

Higher humidity air is less dense, just ask any aircraft pilot. To understand that ... just recognize that water vapor is H2O and air is about 78% nitrogen, 21% oxygen each of which is a diatomic molecule.

So, going back to my high school chemistry, 1 mole (22.4 liter at STP) of air weighs 0.78*2*14 + 0.21*2*16 grams, or about 60 grams. 1 mole (again, 22.4 liter at STP) of water vapor is 2*1+16 grams, or about 18 grams.

gar, you're the expert on these things ... isn't this true?
 
I would ask whether at temperatures well beow its boiling point water vapor behaves as an ideal gas. But your argument seems logical at first examination.

Sent from my XT1585 using Tapatalk
 
It is not the humidity or water vapor in the air that prevents static electricity build up, but a thin film of water on the surface of the materials that lowers the resistivity.
http://amasci.com/emotor/humid.html

Here is a more technical paper, see page 39 for a plot of humidity vs breakdown voltage of air.
http://ethesis.nitrkl.ac.in/2875/1/Full_Thesis_Print_04.07.2011.pdf

This does not mean that powerlines are better off during periods of high humidity or rain, because they produce corona & it's presence during high humidity increases the likelihood of a flashover.
https://www.pupman.com/listarchives/2003/November/msg00428.html
 
Status
Not open for further replies.
Top