Earth-return Circuits Research Articles

Case Studies in 50-bit/s Leased Lines: Modem Communication Failure at Earth-return Circuit and the Cause of Failure to Replace Metallic Transmission Line with Optical Cable

Case Studies in 50-bit/s Leased Lines: Modem Communication Failure at Earth-return Circuit and the Cause of Failure to Replace Metallic Transmission Line with Optical Cable

Interaction between a DC Traction System and an AC Power System Through Earth-return Circuits

The article describes a problem that occurs in electrified railway transportation, involving the interaction between the earth-return circuits of different power systems. One of the analysed circuits is the earth-return circuit of a high-voltage power grid, the other is the return path of a 3 kV DC traction power supply system. The paper presents the results of the field tests carried out so far and discusses a mathematical model developed in the Matlab-Simulink environment with the aim of determining the interaction between both of the said systems. Keywords: earthing, traction substation, traction return system

Models of traction stray currents interaction with the earth return circuits

Models of traction stray currents interaction with the earth return circuits

Stochastic stray currents effects on earth return circuits (underground pipelines)

Stochastic stray currents effects on earth return circuits (underground pipelines)

Assessment of d.c. traction stray currents effects on nearby pipelines

Purpose – dc electrified traction systems are a potential source of stray currents. The purpose of this paper is to evaluate the harmful effects (electrolytic corrosion) that an electrified railway has on nearby earth return circuits (e.g. pipelines). Design/methodology/approach – The electric circuit approach, based on the earth return circuit theory, to model stray currents interference on extended structures is presented. An exact method of calculation is applicable to any dc railway system in which tracks can be represented by a single earth-return circuit (equivalent rail) with current energization. In the approximate method, the equivalent rail with current energization is modeled as a large multinode electrical equivalent circuit with lumped parameters. The circuit is a chain of basic circuits, which are equivalents of homogenous sections of the rail. The electrode kinetics (polarization phenomenon) is taken into account in the model developed. Findings – Formulas in partially closed forms are derived applicable to the analysis of currents and potentials along a pipeline laid in the proximity with railway tracks. The attempt is undertaken, to incorporate the electrode kinetics into the simulation model in which the polarization phenomenon (Tafel equation) is modeled by a non-linear voltage source with source voltage being iteratively calculated. The polarization potential along the affected pipeline can be determined. Originality/value – The pipeline electrochemical response (polarization behavior – non-linear phenomenon on the interface metal-soil electrolyte) to the dc stray currents interference is innovative incorporated into the simulation model with lumped parameters using the iterative process.

Mutual impedance of non‐parallel conductors with earth return

AbstractThe calculation of currents and potentials along underground conductors (telecommunication and power cables, pipelines) occurs in many practical problems associated with interference from currents in power transmission lines or electrified railways lines. The knowledge of the mutual impedance between both earth‐return circuits is essential in case of inductive influence. The mutual impedances of long conductors may be derived using the Carson method. The formulas, however, apply only to parallel conductors. In case of non‐parallel conductors an approximation method overcomes this problem by segmenting the angled conductor along its length. In the paper the alternative approach is proposed, based on the linearization of the mutual impedance characteristic for 50 Hz. The use of the linear regression method leads to accurate results of calculation of potentials excited by the inductive effects of a transmission line on non‐parallel underground conductor.In the paper the method of determination of the mutual impedance of angled conductors with earth return is also developed for the case when one of the conductors is finite in the length. The formula for the mutual impedance contains an integral, which does not have an analytical solution. A numerical integration algorithm is developed. The exemplary calculations show that the use of the algorithm developed leads to results with considerably accuracy. Copyright © 2009 John Wiley & Sons, Ltd.

Proposal of earthing resistance measurement method without auxiliary electrodes

This paper proposes an earthing resistance measurement method for a simple earthing electrode without two auxiliary electrodes. The proposed method can measure the earthing resistance by evaluating loop impedance of an earth return circuit composed of an earth electrode of the under test and a lead wire, a return wire, and the earth soil. The return wire is placed on the soil surface without any terminations. The earthing resistance of the electrode of the under test can be given by the earth return circuit impedance at a resonant frequency design between 100 kHz and 1 MHz. The measurement conditions for the proposed method are determined by numerical calculations. Earthing resistance deviations between the proposed method and the existing method are −13% to +22% for earthing resistance values with 50, 100, or 300Ω. It is found that the proposed method can be used to evaluate an earthing resistance around 100Ω for a simple earthing electrode. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 16–26, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20196

Proposal of Earthing Resistance Measurement Method without Auxiliary Electrodes

This paper proposes an earthing resistance measurement method for a simple earthing electrode without two auxiliary electrodes. The proposed method can measure the earthing resistance by evaluating loop impedance of an earth return circuit composed of an earth electrode of the under test and a lead wire, a return wire, and the earth soil. The return wire is placed on the soil surface without any terminations. The earthing resistance of the electrode of the under test can be given by the earth return circuit impedance at a resonant frequency design between 100 kHz and 1 MHz. The measurement conditions for the proposed method are determined by numerical calculations. Earthing resistance deviations between the proposed method and the existing method are −13% to +22% for earthing resistance values with 50, 100, or 300Ω. It is found that the proposed method can be used to evaluate an earthing resistance around 100Ω for a simple earthing electrode. © 2005 Wiley Periodicals, Inc. Electr Eng Jpn, 154(3): 16–26, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20196

Computer simulation of responses of earth‐return circuits to the AC and DC external excitation

AbstractThe use of the circuit simulation package SPICE (Simulation Program with Integrated Circuit Emphasis) permits the complex analysis of the EMI (electromagnetic interference) on earth‐return circuits. In the approach presented, the earth‐return circuit with excitation by AC signals and transients, as well as with DC energization is modelled as a large multinode electrical equivalent circuit. The circuit is a chain of basic circuits, which are equivalents of homogenous sections of the earth‐return circuit with uniform exposure to the primary interfering electric field associated with the inductive and the conductive influence. The application of controlled voltage and current sources in the basic circuits permit the modelling of coupling effects in systems of earth‐return circuits. Contrary to the analytical methods the SPICE simulation enables one to solve the EMI problems in practical cases connected with: topological complexity of the system considered, non‐homogeneous geometrical and electrical parameters of the earth‐return circuits, non‐homogeneous earth, application of insulating flanges, bonds, earth electrodes in a system of earth‐return circuits, non‐linearity of the system, etc. The SPICE simulation is an alternative and a useful approach to the analysis of EMI problems in earth‐return circuits, when comparing with existing analytical and numerical solutions. The usefulness of the SPICE simulation has been illustrated by examples.

Effects of toroidal HVDC ground electrode on earth‐return circuits

AbstractThis paper presents a method of evaluation of currents and potentials, excited by conductive effects of high‐voltage direct‐current (HVDC) transmission system, along two parallel earth‐return circuits such as pipelines and cables buried in the vicinity of a toroidal ground electrode. It is assumed that the system considered is linear and that the earth is an isotropic, homogeneous medium of finite conductivity. Conductive coupling between earth‐return circuits is taken into account, whereas the reaction of the conductors' currents on the electrode current is disregarded. The transmission line model of the conductor with earth‐return, a segmental linear approximation of the curve of the primary earth potential distribution along the conductor and the concept of superposition have been used in the method. It should be pointed out, that the method does not require the time consuming numerical integration. The technical applications of the method are illustrated by examples.

Simulation model for drainage protection of earth-return circuits laid in stray currents area

Proper design of drainage protection against stray currents requires the knowledge of current and potential distribution along the rails of the d.c. railway system and the installation to be protected (cable, pipeline, etc.). Usually, a calculation model is used in which these earth-return circuits are treated as separate. In reality, the protected structure and the rail can be placed close together and conductive coupling between them exists, resulting in different current and potential distributions along both structures when comparing with the case of the separate structure. In this paper, a calculation model is presented in which an interchange of currents flowing along both structures – equivalent rail and protected structure – is taken into account. The formulae in closed forms are derived for calculation of such parameters as longitudinal current, potential to the remote earth, and potential to the adjacent earth. An attempt to incorporate electrode kinetics into the model is also made. In the simulation model, the polarization phenomenon is modeled by an iteratively calculated non-linear resistance. Example calculations are carried out in which the influence of the resistance of the drainage connection and the drainage current on the protection efficiency are examined. The relations presented may be useful at the design stage of protection systems containing electric drainages.

A calculation model for cathodic protection of underground extensive structures using impressed current cable anodes

Proper design of cathodic protection by use of impressed current cable anodes requires the knowledge of current and potential distribution along the anode and the structure to be protected. The conductive coupling between these earth-return circuits results in different current and potential distributions along both structures when comparing with the case of separate anode. In the paper calculation models – accurate and simplified – are presented. In the accurate model an interchange of currents flowing along both structures is taken into account, whereas in the simplified method the structures are treated as separate earth return circuits. The formulas are derived for calculation of such parameters as longitudinal current, protective current density, potential to the remote earth and potential to the adjacent earth. Calculations have been carried out in which the influence of the distance between the two structures on the values and distribution of currents and potentials along the anode and the protected structure has been examined. The relations presented may be useful at design stage of impressed current cathodic protection systems containing cable anodes.

A universal model for the computation of the electromagnetic interference on earth return circuits

The increasing size of modern electricity supply systems, as well as the higher operating and short-circuit currents of the high voltage systems have been matched by an over-spreading network of earth return circuits (pipelines, cables, etc.) close to high-voltage installations, resulting in a closer inductive and, in the vicinity of earth electrodes, conductive coupling of both system types. The view of the acceptance or inadmissibility of these interferences resulting from the couplings requires the quantification of the physical effects. A computer-simulation leads to reliable forecasts with respect to system stresses and suitable countermeasures. A universally valid algorithm for the calculation of interference voltages and currents in networks of optional topology or with several exposures to power lines is presented and applied to practical problem cases. The algorithm developed is superior to existing models as it simulates uniformly both the inductive and the conductive effects on earth return circuits. >

Outer conductor shields and electromagnetic fields around delay–type inductive communication cables

AbstractTwo kinds of delay‐type inductive communication cables in actual use for mobile communication are shown theoretically and experimentally. They are characterized by two different types of outer electromagnetic fields, that is, convergence type and induction type, according to the shield construction of the outer conductors. The convergence type aims at limiting the communication region by using the wavelength reduction rate in a cable; the induction type aims at generating a relatively strong outer electromagnetic field. Despite the similarity of their appearances, these two kinds of cables are shown to have entirely different usages, characteristics, and mechanisms of generating electromagnetic field. This paper studies the shield effect of the delay‐type line outer conductor, especially the phenomenon of outer electromagnetic field generated by earth return circuit as a result of the imperfect shield effect of outer conductor for longitudinal electric field. This field interferes with the main wave in the case of the convergence‐type cable, and is a dominant main wave in case of the induction‐type cable. These two kinds of cables have already been developed and are now in use.

Calculation of closed earth-return circuits containing conductors energized by direct currents

A method of calculating non-equipotential closed earth-return circuits, each of which contains n points of current energization and current outflow, is presented in the paper. A mathematical model and an algorithm for its solution are included. In this method the electrical properties of conductors are described by means of unit-length and wave parameters. Numerical calculations of potentials along railway rails are made on the basis of the presented algorithm. Conclusions are formulated from an analysis of the method.

A method of calculating currents and potentials along parallel earth-return circuits containing underground conductors supplied by voltage

The first part of this paper deals with the method of calculating electrical parameters in parallel underground conductors for frequencies up to 1000 Hz. In the second part the case of parallel single conductors is considered and a substitute electrical diagram is determined for them. Linear homogeneous differential equations are presented for this diagram. Only a special solution of those equations is given. Considerations concern a symmetrically-located AC voltage supply source of one of the conductors while the voltage is equal to zero in the second conductor. For such a case a method of calculating the currents and potentials along infinitely long and parallel underground conductors constituting magnetically coupled earth-return circuits is presented.

Currents and potentials in earth-return circuits exposed to alternating current electric railways

This paper presents a method of calculation of currents and potentials, excited by the electromagnetic effects of an AC-electrified railway system, along two infinitely long earth-return circuits buried in parallel in the vicinity of the tracks. Inductive and conductive coupling, exists within the railway system, and the earth-return circuit is taken into account, as well as interaction between currents flowing in both underground conductors, whereas the reaction of the conductors' currents on the track current is disregarded. The analysis given is applicable to any railway system in which the tracks may be represented by a single conductor with earth return. The technical applications of the method are illustrated by examples.

Project Sanguine Interference Mitigation Research

The Navy's proposed extremely low frequency (ELF) communications system (Sanguine), which would use an earthreturn circuit to excite the earth-ionosphere cavity, represents a potential electrical interference problem. The electromagnetic fields produced by Sanguine could influence other systems such as power distribution lines and telephone circuits, and other very long electrical conductors. This interference potential and the techniques useful in mitigating it are described. Also, data on power and telephone systems are presented that were useful in communications systems design tradeoff studies.

Image Theory Results for the Mutual Impedance of Crossing Earth Return Circuits

Suitable engineering expressions for the mutual impedance of crossing earth return circuits are derived by employing finitely conducting earth image theory techniques. It is shown that the image theory and previously derived analytical results, which are rather complicated, are in excellent agreement.

ELF Earth Return Coupling Into Power Systems

With the advent of the U.S. Navy's proposed ELF Communications System (Sanguine System), which would use an earth-return circuit to excite the earth-ionosphere cavity, earth-return current coupling into power systems has become important. The theoretical basis for coupling into power distribution systems is developed. A comparison is made between measured and predicted values of the induced voltage. Techniques which are useful in eliminating the effects of the induced voltage are described. The effectiveness of these interference mitigation techniques is demonstrated by comparing measurements on actual systems. Finally, data on power system interference are developed for use in communication system design tradeoff studies.