Electric Field Induction from the Institute of Electrical and Electronics Engineers:
"Induced voltage in a transmission line due to its proximity of another transmission line in the same right of way is often erroneously considered to be solely the result of electromagnetic induction. In general, electromagnetic induction is a function of the loading of the energized line, the proximity of the two lines and the distance that they are paralleled. Most utility personnel are not aware that large voltages can be developed from electric field induction.
Unlike electromagnetic induction, electric field induction is a not a function of the distance that the two lines are paralleled. It is primarily a function of the proximity of the two lines and the magnitude of the operating voltage of the energized line." (from Induced Voltage in Parallel Transmission Lines Caused by Electric Field Induction) http://ieeexplore.ieee.org/Xplore/login.jsp?url=/iel5/4144487/4141002/04144488.pdf?temp=x
Electromagnetic Induction from NASA education:
"The Induced Electric Field"--"A magnetic field is a region where at any point a magnetic force can be observed . . . Similarly, an electric feld is a region of electric forces. . . In particular, if an electric conductor (i.e., irrigation pipeline, watering trough, Owyhee Siphon, etc. ) is placed in an electric field, an electric current . . . will usually flow. If the conductor is a metal and obeys Ohm's rule--as in insulated copper wires used in electric machinery--the current will flow along the wire, its shape depending on that of the wire, and its magnitude on the electric resistance of the material, which depends on thickness, length and material. In addition, various rules need to be obeyed:
- The circuit must be closed, otherwise electric charges carried by the current accumulate at its ends and those accumulations create their own electric field, stopping the flow of any additional current.
- If a current does flow, it contributes its own magnetic field, modifying the one creating it and generally weakening it.
- If some more complicated relation takes the place of Ohm's Law (as happens, for instance, in plasmas), that relation rules the current flow, often making it more complex.
- And... if there is NO electric conductor in the region of changing magnetic field, NO electric current flows. However, there still exists an "induced" electric field, a modification of the properties of space, though without any material on which it acts, it would be hard to detect it.
The high voltage requires the transmission lines to be extremely well insulated from their surroundings, which is why they are strung high in the air (air is an excellent electric insulator), (except when the lines sag as we have seen) hanging from elaborate ceramic supports (ceramic insulates too). . . " http://www-spof.gsfc.nasa.gov/Education/wEMinduc2.html
Transmission Line Safety and Nuisance from CA DOE http://www.energy.ca.gov/sitingcases/riverside/documents/applicants_files/SPPE_application/04%20T-Line%20Safety%20RERC%20SPPE.pdf
Electric and magnetic fields (EMF) are present wherever electricity flows: around appliances and power lines, in offices, schools and homes. Electric fields are invisible lines of force created by voltage, and are shielded by most materials. Units of measure are volts per meter (V/m). Magnetic fields are invisible lines of force created by electric current and are not shielded by most materials, such as lead, soil and concrete.
Electric Induction – Agriculture Equipment (page 10)
Agricultural equipment can have dimensions approaching those of large road vehicles and as such can be subject to similar electric field induction levels. In practice, the conductivity of tires and good contact with the soil usually insures that electric field induction on farm equipment is seldom perceived.
Irrigation systems often incorporate long runs of metallic pipelines, which can be subject to magnetic field induction when located parallel and close to power lines. Because of the pipes' contact with moist soil, electric field induction is generally negligible, but annoying currents could still be experienced from magnetic coupling to the pipe. Pipe runs laid at right angles to the line will minimize magnetically induced currents although such a layout is not always feasible. Common mitigation measures are grounding and/or insulating the pipeline runs. (Another cost to farmers.)
Operation of irrigation systems beneath power lines presents another safety concern, particularly for systems that can project the water to conductor height. This concern is not caused by induction, but rather by the possibility of direct contact by conductive water. The water stream from a high-pressure nozzle generally consists of a solid and broken-up portion. If the solid stream contacts an energized conductor, electric current conducted down the water stream may be hazardous to someone contacting the nozzle. Line contact by the broken-up part of the water stream is unlikely to present any hazards.
Although there are these legitimate concerns regarding irrigation systems, the only known and unfortunately not infrequent cause of serious accidents is inadvertent contact to lines by upended irrigation pipes, often during an attempt to remove a small field animal that has crawled into the pipe. For this reason, irrigation pipes that are very close to any power line should be moved with caution. The pipes must never violate a safe electrical clearance space around line conductors. (What about line conductors violating a safe clearance space around irrigators?)
Magnetic Induction - Pipelines
Metallic pipelines can be within the transmission line right of way. Magnetic fields penetrate the ground and significant impacts can occur with long pipelines (there is not an established length but typically pipeline lengths more than 1,000 feet become more of a concern). Maximum voltages on the pipeline occur where there are discontinuities in either the transmission line or pipeline. When the transmission line and a pipeline are interacting, such discontinuities take the form of rapid changes in:
• Separation or termination of the pipeline and transmission line or insulating junction
• Sudden changes in pipeline coating characteristics
• A junction between two or more pipelines or transposition of transmission line phases
Note that the induction effects on pipelines during normal power line operating conditions are small compared to the induction effects experienced by a pipeline during a power line fault. The most severe kind of fault is a single phase-to-ground fault, during which high currents circulate in one of the power line phases and are not attenuated by any similar currents in other phases. Hence, fault reduction methods that suffice for single-phase fault conditions are often adequate for other conditions. In spite of the relatively low magnetic field levels during steady state conditions, induced voltages on an unprotected long metallic structure can reach hundreds of volts. The highest magnetically induced voltages occur for a fault condition since the currents in the line can be an order of magnitude greater than the normal or emergency load current. Even with extensive grounding systems connected to the structure, pipeline potentials can be on the order of dozens of volts, with hundreds of amps flowing in the structure. This constitutes primarily a shock hazard, which can be transferred miles away from the parallel corridor. In magnetic coupling studies, it is important that power lines as far away as 1,000 feet or more from the power line under study be given serious consideration.
Generally, there are three techniques to reduce the potential for high magnetically induced voltages below unsafe levels for fences, pipelines and railroad track systems:
• Sectionalize the conductor system – electrically isolate the pipeline, fence, etc. in sections to keep the voltages down to a minimum without the opportunity to build up over long distances. (Another cost to farmers.)
• Ground the conductor system – put grounds on the conductor system at key locations where the conductor system and transmission line change characteristics and locations relative to each other.
• Buried fault reduction wires – install another system of parallel conductors to the pipeline, fence, etc. at key locations to allow the voltages of the multiple conductors to equalize to a common potential thus creating a low potential difference across a person’s body that will not be unsafe. (Another cost to farmers)
My best technique: Move the proposed transmission line and spare us all this induction anxiety.
