Intensity of the Magnetic Field

It's simple physics. If H_i is higher, then I_i is higher. Your network is probably unbalanced.

Current is higher or you're not measuring the field strength at the same distance, R, from the conductor. The H field drops off as 1/R.

Dear sir

thank you very much for your response

but ,please what mean by (The H field drops off as 1/R.)

thanks

I will try to explain it. A current flowing through a wire creates a magnetic field that circles the wire. We call this field the H field. It is a vector field, meaning that at any point the field has a magnitude and direction.

If you take a circle centered on the wire and you multiply the H field tangent to the circle times the circumference of the circle, it gives you the current flowing through the wire (by Maxwell's laws). The further you are from the wire, the larger the circumference (C=2πR), so the H field will be inversely proportional to R. The circumference times the H field will always give the same answer for the current. (This is called a line integral)

You may be more familiar with the B field. The B field is the H field multiplied by the permeability, μ, (which depends on the material). B=μH.

And other ferrous metal in the area could affect your readings.

Is your 400kV network overhead, underground, GIS? What is the configuration of the lines, trefoil, flat, transposed? How did you get close enough to a 400 kV line to measure the field intensity of each phase? Don't forget that a Hall-effect Transducer will show the vector sum of the magnetic field from all sources combined, and distance matters a lot.

Dear sir

Thank you for your respone

our 400kV network is overhead line, configuration of the lines is triple wire for

each phase,when i measured the Intensity of the Magnetic Field by 3D

measurement of the magnetic field(Gauss meter) i stood under phase /R

then phase /S then phase /T .In other words,the distance for all measurment was

symetrical

Thanks for the feedback! So your OHL is configured flat like this O----O----O and is ordered R-Y-B. Where is the tower in relation to the conductors? What is the distance from the middle phase to ground, and are there any underground conduits/pipelines running parallel with the phases? How long is OHL and are there any transpositions? Did you also record the individual line currents during your tests?

If the lines are side by side, then it's not really symmetrical. What are the distances between the wires compared to the height? Any reading directly underneath one line would also see the field from the other lines, depending on the distance of separation, and the center line would have more interference.

I would be suspicious that the electrical field would interfere with the electronics of your current sensor.

Here is a paper on remote sensing of current on lower voltage HV power lines. The sensor must be mounted on the power pole closer to the wires, and the geometry is taken into account in measuring the currents.

http://www.cired.net/publications/cired2001/1_55.pdf

Dear sir

Thank you for your interest

but the problem now, when we need to open the control panel door for 400KV

circuit breaker which that place approximately under the wire for the R/phase

We feel the presence of electricity and we can not touch the door knowing that the

door grounded.

best regards

That is a totally different problem, your cabinet is not properly bonded and/or grounded, you are feeling what is known as "touch" or "step" potential.

Does the measured value of magnetic field include that(how much) of the earth?.