How to Define the Direction of Current?

I think... that the right hand rule applies. In theory, the orientation of a magnetic field produced by a current in the wire will be a product of the direction of that current. The "Right Hand Rule" specifies that direction when the hand is held out as if you are hitchhiking. The thumb denotes the current direction with the fingers denoting the magnetic field's direction or sense.

All is well and fine for a DC signal. However, if it is an AC signal the current switches back and forth! A 60 Hz AC current reverses every 16.67 mS.

So, if your question is for an AC transmission line, my answer is the current goes both directions! ;-)

Quick correction. In a 60Hz AC line, current changes direction every half cycle which is 8.3ms.

Doesn't matter if the correction or the current is quick or not -- if it's alternating . . . :-0

Okay. At T=0 the current goes positive. At T=8.33 mS the current goes negative.

My 2 cents... Now lets add the load...if it's reactive: capacitive loads will store electric field (for voltage) and thus lag (in time, phase) for voltage but lead in current, whereas inductive loads will store magnetic field (for current) and thus lag (in time, phase) for current, but lead in voltage. So, the type of load will determine synchronization of when current and voltage go positive or negative relative to each other, but the 1/2 cycle rule still applies for reversals. Incidentally, the bi-direction of the AC current is tested by using a current loop meter. Only one of the AC leads can be used to determine the current. If both are used the current will indicate zero due to cancellation of the fields. Try it! Happy hacking.

And to answer your question specifically: Use a simple transformer with the coil parallel to the transmission line and watch the current flip back in forth (in opposite direction of flow in trasnmission cable).

If you ask this question, may I suggest that you stay far away from H.V. power lines?

Very well said. There is no non contact way to do this task. If it were requiredto measure highvoltage DC one could use a compass or some inductive meathod. If the circuit could be interupted a True RMS meter could be used, if a non invasive meathod has to be used a clamp meter could be used. Sorry but as described the situation has no solution. Try locating the power lines on a map and see if you can find the generator, or load.

Arrrggghhh! How about a large aperature induction coil held underneath the HV conductors such that the magnetic flux from the transmission line passes through the aperature of the coil? The strength of the magnetic field is directly proportional to the current in the conductor, although absolute value measurements would not be possible without calibration. Spacing of different phases of polyphase conductors and distance from induction coil must be around the same order of magnitude for significant differences to be measured, but it is certainly a non-contact method of measuring current, similar to the method of using CT's (current transformers) to measure current in electrical processes.

You folks have over-engineered this...simply climb the tower and swing from any conductor...break the line in front of you and which ever hand catches fire and explodes first is the direction to the power plant... The question I have is why somebody would want to know this information....

You will need two things, one, a clamp probe, and two, a voltage probe connected to an oscilloscope.
You can find out which direction the load is and which direction the source is from determining which direction the current flows when a positive or negative voltage differential is on two lines.
The current meter will have to be connected around one of the lines. However, the voltage probe, if properly applied does not have to actually touch either of the lines, just be in proximity to them, making CERTAIN that they are not close enough to arc between the two lines. The high voltage should create enough capacitive coupling to generate a voltage waveform. From that waveform, a polarity can be associated to the polarity current signal. Good luck and understand that information provided here is purely for your knowledge and should not be applied unless you are authorized and fully trained on the utility lines mentioned.

Yes the right hand rule.