# Lightning Earthing Impedance Measurement Project

Hi,

I would like to seek guidance on the development of the Lightning Earthing Impedance Measurement Project.

The brief overview of the project is as follows,

This overview outlines the concept of measuring the earthing impedance with the variable frequency AC source to predict the behaviour of power transmission earthing system under the influence of transient fault / switching transient / lightning transient conditions.

In practice, the impedance of earthing systems is measured at power frequency to gauge the effectiveness of earthing system. The power system frequencies are 50/60 Hz. However, the frequencies under the various abnormal conditions could be several tens of kHz due to the transients generated in the system during fault conditions / switching transients / lightning transients. The earthing system is expected to efficiently absorb the high currents produced under these abnormal conditions. This calls for the characterization of the earthing system at various frequencies ranging from power frequency to several tens of kHz.

Following are the steps of such a measurement

A) Low distortion sine wave generator produces variable frequencies ranging from 10Hz to 100kHz @ typically 10 volts peak to peak.

B) A power amplifier of 100kHz bandwidth amplifies the signal produced by the sine wave generator to a level of typically 1kW to constitute a variable frequency AC source.

C) Variable frequency AC source injects the current into the earthing system at the various frequencies of interest (typically ranging from 10Hz to 100kHz).

D) The rise of earth potential at the point of injection of current in the earthing system is measured with the differential voltage probe (100kHz bandwidth).

E) Injected current magnitude is monitored with the wide bandwidth (100kHz) current sensor.

F) The acquired waveform of current and voltage are processed through the lock-in amplifiers / software filtering to minimize the effects of various noise such as power frequency noise, power system harmonics, traction noise, broadband noise, communication signal noise etc..

G) The RMS value of voltage and current are obtained from the filtered waveforms.

H) The ratio of RMS voltage to RMS current is obtained at various injected frequencies to show the value of earthing impedance of the system under test.

I) The magnitude of earthing impedance in ohms is plotted against the frequency in Hz in log scale to exhibit the behaviour of earthing systems under the influence of various frequency conditions ranging from 10Hz to 100kHz.

I look forward to useful suggestions from the forum members with regards to the development of the above mentioned Lightning Earthing Impedance Measurement System.

Regards

Deepak

Hi, welcome to the forum.
You can paste a link in your post. Like this: Experimental investigation into the performance of large-scale earthing electrodes -ORCA
I think you need a laptop with a data-aquisition device. I don't know how an Arduino board could help with this.

I have a conceptual concern with your project.

It seems all very well to characterise the various cables and connections in your earthing system as they are linear components.

What I suspect you cannot readily characterise, is the impedance of the ground itself, as I suspect it is extremely non-linear and you would have to generate something like artificial lightning bolts to replicate its actual behaviour!

1kW amplifiers and lightning simulators both sound like ways to start fires and/or
electrocute people in the building.

Its possible to measure resistance without high power levels or voltage levels.

The non-linearity is in our favour since a system with a low impedance at 10V
(say) will have as low or lower impedance at 1kV (until something fuses).

I would think limiting the injected current to a few amps and a few volts ought to
be adequate - it begs the question how you complete the circuit (via another
temporary earthing point? At the main earthing post?)

sort of test, territory-dependent...

Paul__B:
I have a conceptual concern with your project.

It seems all very well to characterise the various cables and connections in your earthing system as they are linear components.

What I suspect you cannot readily characterise, is the impedance of the ground itself, as I suspect it is extremely non-linear and you would have to generate something like artificial lightning bolts to replicate its actual behaviour!

Quite.

Its one thing to characterise ground for an electrical safety pov.
Quite another to predict lightning.
It does not follow ohms law unfortunatley

I agree with Paul__B and Boardburner2, the resistance can be an indication, and it would be nice to measure that for a complete country. However, lightning is something completely else.

The lightning can for example connect iron ore in the ground and a resistance measurement can not.
The massive amount of energy does repel to itself. The charge could still go to the ground surface and spread there, while the resistance measurement only measures the resistance to earth below the surface.