Advice on toroidal inductor design for power harvesting

[Viroos]

Hi, I'm a mechanical engineer, but occasionally do some electro-mechanical systems too, but I feel that my knowledge in EE is insufficient. Now I need to design a toroidal inductor in order to harvest power from overhead high voltage lines. How to do it right? The winding should be "simple" or like in Rogowski coil? The core should be iron, ferrite or laminated steel? Thanks!

 

[davidbeach]

That would be called theft.

 

[System Protection]

 

[waross]

Now I need to design a toroidal inductor in order to harvest power from overhead high voltage lines.

That may be more difficult than you imagine.
For best efficiency the toroidal core should encircle the high voltage conductor.
That will be difficult to do while maintaining safe clearances.

 

[Viroos]

That would be called theft.

The design is for the electric corporation itself.

That may be more difficult than you imagine.
For best efficiency the toroidal core should encircle the high voltage conductor.
That will be difficult to do while maintaining safe clearances.

I make it as two halves.

 

[waross]

The toroidal core would best be part of a conventional power transformer.
At that point, toroidal doesn't matter much.
For very small loads such as electronics packages, a Potential transformer may serve.

The amount of power available to harvest by non-contact means is related to the strength of the magnetic field which in turn is current dependant.

The minimum clearance at which flashover occurs may make an encircling core unrealistically large.

 

[Viroos]

The device is attached to the power line with no grounding and is used to charge a battery.

 

[waross]

Attach a Potential Transformer to the power line.
Select a 120 VAC battery charger within the capacity of the PT.

A toroid?
For non-contact induction harvesting a toroid must encircle the primary conductor.
If you are able to install an insulator similar to a transformer bushing around the conductor you may be able to use a bushing CT.
Be aware that the output will be a current proportional to the line current and that the voltage will be determined by the current times the load impedance.
Be aware also that the open circuit voltage will be very high.
Lethally high.
Often high enough to puncture the insulation of your winding and thus destroy your transformer.
A Capacitive PT may be safer if you are able to find one that will develop sufficient current.
Or, if you really want to harvest from the magnetic field surrounding the conductor, consider a straight core so that the magnetic flux may enter at one end and exit at the other end. Mount the core so that it is perpendicular to the current carrying conductor and that the windings are parallel to the conductor.
Feed the output to a bridge rectifier and a zener diode and then to the battery.
It MAY charge the battery, SLOWLY or EVENTUALLY. (Or maybe not)
Ps, We'll watch for you. What province and under what name will we see your obituary?

 

[bacon4life]

Assuming this is for medium voltage. At transmission level voltages, line mounted electronics are quickly damaged by stuff like corona and partial discharge.

Lots of vendors already make self powered devices like fault indicators, marker ball light or line current sensors. Having purchased various devices over the years that were line powered, it seems like there is a pretty big learning curve for vendors to make a power supply that works reliably when clamped to a medium voltage conductor.

Any chance the electric corporation can partner with someone who already makes a functioning scavenging supply? My experience is that vendors are quite eager to help when utilities offer to participate in testing of new products.

Do you have a goal for how much energy to scavenge, as well as the minimum current you want the device to still function at?