Getting power from transmision lines electromagnetic field 2

[Bronzeado]

Hi folks,

In developing countries, corridor of transmission lines run nearby small villages with no electricity. This seems to be very unfair to people from those villages.

There is an ideia of getting power (1-2kW) from the electromagnetis field of the transmission lines to feed those village. I wonder if somebody has information on this kind of development.

Best regards,

Herivelto Bronzeado

 

[waross]

Thanks for your efforts, Gunnar, cranky108 and davidbeach.
Consider the familiar configuration of a trefoil arrangement of three conductors on a pole or tower. the center conductor high, in the center, and the other two conductors lower on a cross arm. Now visualize a second cross arm lower on the same pole. The spacing below the first cross arm would be equal to phase to phase spacing. A "pick-up conductor would be run below each phase conductor for a mile or so. I suspect that the results will be much better than Gunnar found in his experiment, but still inadequate.
I am tending towards bushing style CTs installed on insulator strings.
Another possibility, a voltage divider using 35 kV power factor capacitors. The capacitors could have their cases mounted on insulators suitable for the transmission line voltage.
A small 35 kV distribution transformer would be connected in parallel with the last capacitor in the string.
The advantages are;
1, This would help the line power factor slightly.
2, The major components will probably be in stock, the capital outlay for a pilot project will be small.
3, I imagine that the effect of tapping small amounts of energy from a transmission line may be in the order of magnitude of the unbalances resulting from poorly designed transpositions.
Will this work? What will we need for over voltage protection?
Do you see any problems with capacitor banks distributed along your transmission lines, Bronzeado? If we service three villiages, we should not be too unbalanced.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[davidbeach]

Bill, at those voltages there is almost no need for shunt capacitors. Particularly at 500kV you will find that the lines are provided with series capacitors and shunt reactors. The series capacitors are used for line compensation and the shunt reactors are needed for voltage control during light load conditions. Additional shunt capacitance may not be desirable. As Gunnar says, if it were practical it would already be used in practice.

 

[Skogsgurra]

Hi Slava!

You seem to live in a country with some mysterious inverted inflation. You started with a few cent's worth of tips - and now you are down to two millicents? Remarkable!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[slavag]

Oops, it's inflation. I pushhed on the "0" more than needed.
My 2 cent.
Actaully, I understand the Herivelto situation.
Solar is good solution, but is expensive now.
DG is expensive and in additional is request fuel and maintanace.
Taping on the 500kV-unpossible, for few kW's it's ......
Isn't simple situation.
Best Regards.
Slava

 

[scottf]

A few points:

1. I can't see any scenario where any kind of CT can be used to provide an appreciable amount of power, evenif we disregard the system conditions issue (i.e. varying current levels in transmission line).

2. There exists a device called a Power Voltage Transformer. These are commonly used to provide station power from transmission line voltages, but are sometimes applied to supply power to villages and camps. There are commonly available up to 230 kV and 100 kVA. There are also units available at 345 kV, with ratings close to 33 kVA.

There have been projects in South America and Asia, where the rated secondary voltage of these PVTs were in the 15 kV range and small distribution networks were run from them. Since the PVTs inherently have a high impedance, regulation has to be addressed on the LV side. However, this high impedance also offers the advantage of low available fault current levels on the LV.

I've seen transmission line tap points as simple as a 230kV to 15kV PVT and an arrester installed on the side of a transmission tower. 15 kV line runs down tower and into camp and a few distribution xfmrs are placed in the camp to power the small building.

Price of a 230kV/100kVA PVT is approx. $100k.

 

[slavag]

I will think about this one:

http://www.offshore-technology.com/contractors/power/ormat/

 

[civilperson]

The price of a standard substation with transformer down to 15kV or 3kV is over two million dollars, (assuming dual three phase components). This may be amortized over many years and many customers but the accountants have the final say as to profitability. The villagers need a minimum standard of living to afford this infrastructure. Even US Rural Electrification Cooperatives required subsidies to succeed. Local wind or solar generation could be the first step with excess power sold to the grid owners.

 

[Bronzeado]

Thank you guys for your efforts.

Initially, I would like to say that things are normally done because who does did not know that they are impossible.

Gunnar, I agree with most you said:

“It will probably be possible to build an isolated platform and put a piece of conductor close to the transmission line so that varying distance would not be a problem. But the safety distance when dealing with 230 and 500 kV is such that the induction between the "primary" and "secondary" will be very small - if you do not apply system voltage insulation. And then, you could just as well use a transformer. With much better results.”

I think that a “hybrid air-iron core transformer” could be used, with the iron being like a half C following the path of the magnetic field created by the lateral phase (cable) of the transmission line, with a coil wound on it. In this case, the induced voltage. It will be like a CT broken in a half but not touch the cable. Gunnar, could you do this experience, please? Thank you!

Slava, I think this discussion is more valuable than 0.00002$. Please, rise your offer!
In our region is like yours (I think), to much sun and little water. The distribution company have already tried solar (photovoltaic) technology but had no success. I do not know why. May be because they are expensive and need too much maintenance (?).

Bill, for safety, we do not like things directly connected in the transmission line phase to ground. So, capacitor dividers in remote areas are almost forbidden, as if they loose their ground connection a full voltage will be at that connection. May be in the future, with surge arresters installed along the transmission line to improve its performance, the way they think could change.

David, I think that what Bill said there is no relationship with the reactive compensation of transmission line. Also, the capacitance of these capacitor dividers is insignificantly small when compared with those of the transmission line. I agree with you when you and Gunnar say that “if it were practical it would already be used in practice”. But, remember that the use of things depends on your needs. In this case we need to do something to supply small remote villages and it is important to know if this kind of device is feasible.

Again, I would like to thank all of you for discussing this matter and for playing in this forum.

 

[Skogsgurra]

I like your attitude, Bronzo! If it can't be done - just go and do it!

But, more often than not, it is a sad fact that things cannot be done. The very few exceptions to this are things like the flight of the bumble-bee, putting man on the Moon, making old whisky out of fresh alcohol. The success of the latter is disputed, though...

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[Bronzeado]

Thanks, Gunnar!

Best regards,

Herivelto Bronzeado

 

[cranky108]

Once upon a time, there was a brand of reclosers that used a line ct for a charging the batteries in the recloser. It did not work well for reclosers that were normally open or lightly loaded, but in some cases it did work.
Sort of like wind power, it isen't always there.

Maybe an approch could be a combonation of sources, and a battery set/inverter.

Not the most efficent, but it is another option.

 

[ATBradbury]

hmmn, although of no use to you, maybe the best solution is for power distribution company to fund DC low voltage and small wind turbines that might fit inside a cage to be installed at the top of the pylon, causing negligible stress on the pylon.

The distribution company installs this to fullfill a social obligation, and when their is not enough wind power it may run a device that picks up the alternating field and rectifies it, supplementing the wind turbine, with the devices located in the pylon installation.

This then takes DC at modest voltage off to nearby villages, where it supplies cheap laptop, lighting and refridgeration.

 

[waross]

Thank you scottf for your information.
At $100,000 that is probably the best we can do safely and practically.
divided between 100 or more users and amortized over 10 years this is much more doable than a multi-million dollar substation.
In regards to solar and wind power, they are great if you do it yourself or it is owned by a corporation with a budget for regular service.
However, sad experience with almost all types of social economic development is that giving technology to an unsophisticated group and then leaving them on their own is a waste of time and money. By the way, I have seen a successful development project. A village needed a secondary school. A small group spent months encouraging and empowering the local people. They made quiet suggestions and shared bits of information. Eventually, the villagers had the information and encouragement to form their own school.
The crowning mark of success came several years later.
One teacher resigned to take a position elsewhere. Then the other teacher left. Then the church that had supplied the rented quarters announced that the space would no longer be available. So there was a school with no classrooms and no teachers, and classes were due to start in a few weeks. The folks who had helped the villagers start the school thought that they were going to see another project fail dismally. They were heartbroken and at their wits end as to how to help. Then, suddenly, the villagers realized; If WE don't do something fast WE will lose OUR school. There was a flurry of activity, teachers were found and a classroom was found and school started on schedule.
I realize that this may seem off topic, but I lived with these people for over a year and I remember the lessons learned whenever someone suggests solar or wind power for a remote unserviced location.
Thanks all for the varied information. The next time this subject comes up, we will know what is not practical and more importantly, why it is not practical.
And the $100,000 solution will not appeal to those looking for a free lunch.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[QBplanner]

Bronzeado:
I recall Hydro Quebec once found Mcgill University to do a research on this topic. the rough ideas is to supply some spot loads along the 735kV or 500kV line without putting in step-down Trx. I don't remember all the details but they propose some kind of simple platforms under the line to gether some power from the EMF.
I don't know if they made it or not.
Sorry ca not offer more information.
QB

 

[Bronzeado]

QBplanner,

Thank you for the information.
I will try to find more on this matter with Hydro Quebec and Mcgill University.

Regards,

Herivelto Bronzeado

 

[Skogsgurra]

You tell us what you find? Please. This is getting interesting.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[LMBT]

To power some microwave stations, Hydro-Quebec uses a system that relies on induced voltage on the ground wires. The system is described in the following article.

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=1256405

They say in the article that they use it in around 30 locations with loads in the order of 25 kW buy it could maybe be used up to 300 kW.

LMBT

 

[Bronzeado]

LMBT,

Excelent information.
Thank you.

Regards,

Herivelto Bronzeado

 

[Skogsgurra]

The paper says: 735 kV transmission line, 3 - 4 km, insulated overhead line picking up power, capacitive coupling, special magnetic voltage regulator, heavy overvoltage protection - the overhead ground line still has to do its duty protecting the transmission line, 25 kW.

This is capacitive coupling - not inductive. Power usually goes with voltage squared - that would mean that the 1 - 2 kW mentioned in the OP would be possible also with lower voltages in the transmission lines.

I did search the IEEE site before, but wasn't able to find this very interesting article. Thanks and PLS to LMBT.

Gunnar Englund

http://www.gke.org

--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[waross]

Just as I was about to point out the difference between magnetic coupling and capacitive coupling.
That's a great reference.
This is a great forum.

Bill
--------------------
"Why not the best?"
Jimmy Carter