Calculations
|
|
|
CapabilitiesMagnetic fields are produced by current carrying conductors , e.g., load currents carried by electric power transmission or distribution lines. These fields can couple into above or below ground structures, facilities, and also to individuals. When coupling to individuals, generally, the strength of the field is a concern relative to possible health effects. For coupling to collocated facilities a field proportional to the mathematical integral of the magnetic field commonly referred to as the longitudinal electric field is the driving force that induces voltages and currents unto the structures. Hence, even though the same source field may exist , the analytical procedures for predictive analysis and effects management will differ depending upon whether the coupling is to a person or a metallic structure. ESI has had extensive experience providing predictive analyses, design for field management and induced voltage mitigation, and expert witness testimony relative to both magnetic field coupling situations. The following electric power line field effects research and consulting services are available.
The Iroquois gas transmission pipeline extends for a distance of 370 miles through New York State and Connecticut starting at the St. Lawrence Seaway and ending on Long Island, NY. The pipeline collocates with electric power lines on eleven separate rights-of-way for a cumulative distance of 130 miles. ESI appeared as expert witness for IGTS before the New York State Public Service Commission and the Connecticut Citing Council regarding electromagnetic coupling concerns related to joint rights-of-way usage. Both steady state and fault electromagnetic coupling were analyzed for the purpose of evaluating and ranking alternative proposed routes. Oral and written testimony was provided to the commission and council based upon these studies. In regions of excessive induced voltage levels, mitigation systems were designed and implemented. After pipeline installation, field measurements were made to verify mitigation system operation
The Kern River pipeline is a 36 inch diameter line extending for a distance of 650 miles from Opal, WY through UTAH and NEVADA to Daggett, CA. The pipeline parallels high voltage power lines in UT, NV, and CA for a combined distance of approximately 320 miles. Under subcontract to CH2M HILL, ESI reviewed CH2M HILL steady state induction calculations. Fault current inductive and conductive coupling calculations for the entire pipeline were then made by ESI, with recommendations for mitigation provided as required.
Steady state and fault current induced voltage profiles were calculated for the Empire State Pipeline which parallels a NYPA east-west 345 kV transmission line corridor for 150 miles. A mitigation system which reduced pipeline voltage levels to 15 volts or less throughout the exposure was recommended. Expert witness testimony regarding these findings was presented before the New York State Public Service Commission relative to the application by the Empire State Pipeline Company for a certificate authorizing the construction and operation of the pipeline.
Induced ac voltages for a portion of the Vancouver Island Gas pipeline paralleling an electric power transmission line were calculated. A mitigation design for reducing the pipeline voltages was evaluated. Based upon soil breakdown data, an analysis was made to determine minimum pipeline spacing from electric power facilities so as to preclude direct arcing during power line faults. To obtain soil breakdown data, high voltage tests were conducted in the ESI laboratory. Measurements were made to determine breakdown electric field variability as a function of sample thickness. Using these data, lightning and power line fault current induction effects upon the pipeline were analyzed.
The AMOCO Whiting, IN to Decatur, AL. 525 mile eight inch products pipeline has previously experienced pipe steel failures.. In a joint venture, ESI and Bender Corrosion Associates, by means of combining field acquired data with computer modeling of the right-of-way, have identified locations along the pipeline where susceptibilities to collocated power line fault current induced voltages existed. Improvements to an existing mitigation system for reducing fault current susceptibility levels were evaluated and recommended for installation.
Collocation of electric power transmission lines and railroad facilities on a common right-of-way can result in the coupling of electromagnetic interference into the railroad signaling system. The coupling can cause induced voltages and currents which may compromise the safety and reliability of the signaling system. ESI acted in the capacity of subcontractor to SAIC under an Electric Power Research Institute (EPRI) sponsored contract to aid in the initial development of a railroad track analog circuit simulator which will be used for signal system equipment susceptibility testing.
A 12 inch lateral was constructed from the Iroquois Gas Transmission System pipeline to supply the Substation with a natural gas fuel supply. The lateral is approximately a mile in length and terminates at a meter station at the perimeter of the Substation. Within the substation, the natural gas is transported for approximately 1500 by eight inch high pressure piping of which 450 feet lies beneath the station grounding grid. The piping and the lateral parallel nine 115 kV electric power transmission circuits leaving the Substation. Both steady state operation and fault situations were analyzed to determine induced voltage and current levels on the combined piping and lateral gas delivery system. Remedial mitigative systems were designed to reduce induced voltage levels.
A Chicago & North Western Railroad single track that paralleled a 138 kV double vertical circuit for a distance of approximately six miles experienced high induced voltage levels causing an electric shock hazard. The objective of the study was to determine the cause of the induction and offer remedies for mitigation of the hazard. The approach taken for solution was (1) prepare a computer model of the electrical equivalents of the collocated track and power line circuits to simulate the electrostatic and electromagnetic coupling effects, (2) inspect the site and make electrical measurements on the track and the power line magnetic field to obtain parameters for input to the computer program, (3) exercise the model and compare results with field measurements to determine the cause of the induction, and (4) present and evaluate several alternative mitigation approaches for the elimination of the shock hazard.
This study was concerned with the prediction of electromagnetically induced voltages and currents unto a proposed 20 inch natural gas transmission pipeline which would be collocated in an electric power transmission line corridor. The corridor contained the following circuits; (1) a 345 kV double vertical circuit tower, (2) a 230 kV double vertical circuit tower, (3) a 138 kV double vertical circuit tower, and (4) a 138 kV horizontal circuit H-frame. A future 345 kV double vertical circuit was also included in the study. The corridor was computer simulated and induced voltage and current profiles for the pipeline were derived for both steady state and fault current situations.
DOT CFR 192.467(f) External Corrosion Control: Electrical Isolation states that "where a pipeline is located in close proximity to electrical transmission line footings, ground cables or counterpoise, or in other areas where fault currents or unusual risk of lightning may be anticipated, it must be provided with protection against damage due to fault currents or lightning, and protective measures must also be taken at insulating devices." The scope of this project was to derive a means by which a quick look assessment of the potential hazard imposed by nearby electric power facilities could be made. A computer program was developed which allowed a site specific evaluation as to whether mitigation measures are required in order to comply with DOT regulations.
Under subcontract to CH2M Hill, ESI performed a fault current analysis for the Seattle City Light Department to determine voltage induction levels from an expanded 115 kV electric power system upon collocated water transmission pipelines. The need for mitigation measures was also evaluated and recommendations provided.
ESI provided support consulting services to a Department of Energy study to develop advanced technologies for meeting the nation's future electric power transmission demands. One possible alternative for the development of an increased transmission capability is the expansion of the HVDC transmission line network. In particular, ESI was involved in investigations to provide environmentally acceptable techniques for monopolar earth return operation of dc systems through new deep ground electrode technology that eliminates the adverse side effects of present day earth return methods.
The principal objective of this effort was to develop a computer program having a simplified user friendly interface for predicting and mitigating induced voltage levels for power line/pipeline collocations. Currently available commercial computer programs for electromagnetic coupling studies were reviewed. It was found that these programs with their less than friendly interface generally required specialized expertise to use them, thus requiring the services of outside consultants. Hence, the computer program developed in this project removes a past existing void in computational tools available to the pipeline engineer for assessing the severity of electromagnetic coupling effects and the subsequent design of pipeline mitigation when necessary. Electric power transmission line steady state and fault current scenarios are both addressed.
On a particular right-of-way within the transmission system, a problem was noticed over a period of time that near the ends of several distribution line side taps that relatively high neutral-to-earth ac voltages had been observed. This problem was unique in that the remainder of the electric power transmisssion system did not exhibit this problem. An approach was formulated to determine the cause of these anomalies. Field measurements combined with computer modeling and simulation of these portions of the transmission/distribution system are proposed to determine the cause and subsequent actions that will be required to mitigate the voltages.
At any given time several studies may be underway relative to electromagnetic induction effects when pipelines or other facilities are collocated with overhead ac transmission lines. In these studies, induced voltage levels are determined for both steady state and fault current periods, and if required, mitigation systems recommended and designed. For example, the following studies are currently in progress or recently completed.
|
|
|