measuring and grounding induced voltages in the structures

[panthripu]

Hi guys
I am looking for some information on the title mentioned.The metallic structure very near to the busbar having thousands of ampares are subjected to induction phenomenon . Is it possible to measure these induced quantities (voltages and currents ). Grounding them also has an issue as these quanties are so large that they starts arcing at the terminations of the grounding strip. Any idea or comments please. Any one working in steel melting furances could answer it.

 

[G._S._Ohm]

Start by measuring the voltage drop along a length of the metallic structure. It may be in the mV range.

 

[gar]

121127-0915 EST

To measure the induced voltage (current) in a conductor from a changing magnetic field is difficult.

As soon as you put a 1 turn coil in a changing magnetic field there will be an induced voltage in the coil.

Suppose you have a 10 ft length of EMT and you want to measure the AC voltage drop across that conduit from a current thru it. The desire is to measure the AC resistance. See my photo P21 at http://beta-a2.com/EE-photos.html for making a four terminal resistance of the conduit.

Put one of these terminations at each end of the conduit. Run wires from the voltage points to a meter, and apply a current thru the conduit. If you just made the voltage connections by some loose open wires coming away from the conduit a one turn loop is created with a fairly large window. The current thru the conduit creates a magnetic field that induces a voltage in the one turn loop. This induced voltage might be larger than the i*R voltage drop along the conduit that you want to measure.

How do you solve this problem? Make the loop window just as small as possible. In the conduit case run one voltage lead thru the center of the conduit, and at the end where both leads come from the conduit twist the leads together. A second method is to measure only the voltage from the voltage test leads that is in-phase with the current thru the conduit. A combination of the two methods is also useful.

Note: the induced error voltage in the one turn loop is 90 degrees out of phase with the current.

e = dPhi/dt = K*I*d(sin t)/dt = K*I*cos t

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