# Magnetic toroid - coupling to a power line

1. Jun 9, 2009

### stephen163

I need to obtain a toroid for inductive coupling to medium voltage power lines. The frequencies to be coupled are between 10 kHz and 900 kHz. Bear in mind that at power frequency (50 Hz), the current will be high (up to 100 Amps).

Anyone have any idea on a magnetic material that can achieve this feat? Are there any commercially available products already available to do this?

2. Jun 9, 2009

### chayced

Sounds like the illusive TPU of Steven Mark(s). Good luck, heard about farmers doing this with large coils, but never seen anything conclusive. I doubt you will get any usable power from a HV line unless it's a huge coil. Again, good luck.

3. Jun 10, 2009

### Bob S

Suppose you had a toroid of magnetic length L and realitive permeability u. Suppose it had N turns and an rms current of I. Then the peak magnetic field is

Bpeak = sqrt(2) u uo NI/L
For most magnetic materials, you will need to keep Bpeak below 1 Tesla.

So the maximum permeability you can use is
umax=BpeakL/[1.41 u0 NI]

Using L= 0.2 meters, N=1 turn primary, and I = 100 amps for a toroid, we get

umax = 1130 effective relative permeability.
So you will need to gap the toroid to keep the effective permeability below 1130, even with only 1 primary turn.

In the past, I have used a Rogowski coil for currents up to 100 amps from Magnelab:
http://www.magnelab.com/catalog/uct.php [Broken]
But I have no idea what their frequency response might be.
Another source might be Power Electronic Measurements in Nottingham, UK.
http://www.pemuk.com/

Last edited by a moderator: May 4, 2017
4. Jun 10, 2009

### Staff: Mentor

No, it sounds like he is coupling communication signals onto and off of the power line, not trying to steal energy.

5. Jun 10, 2009

### Staff: Mentor

You need to be careful in at least two ways. The first is obvious -- the shock hazard and safety regulations involved in dealing with high voltages. There are several insulation and spacing rules that must be followed in order to get safety approvals for any device that deals with high voltages. Your liability is huge without getting those safety approvals.

The second problem has to do with FCC regulations (or the equivalent agency if you are not in the US). There are strict limits on what you can couple to power lines -- the limits vary with the frequency of the signals. In addition, some utility companies use communication over their high voltage lines for their own purposes, and would not appreciate you adding an interfering signal in their comm band. See the Utility Applictions section of this page:

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

.

Last edited: Jun 10, 2009
6. Jun 11, 2009

### Bob S

Many years ago I bought a small unit from Sears Roebuck (X-10 unit) that I used to remotely turn on and off appliances and lights. It also worked remotely for lights in my friend's house who lived a block away. I have also seen in Switzerland subscription music being broadcast either on the power line or telephone line in the 50 kHz to 500 kHz band.

7. Jun 12, 2009

### chayced

sorry read inductive coupling and power lines and drew the wrong conclusion. X-10 or any of the other wire communication standards might give you a good starting point.