Underground Conductors Research Articles

Transient Electromagnetic Interference between Overhead and Underground Conductors

Transient Electromagnetic Interference between Overhead and Underground Conductors

An electromagnetic monitoring method based on underground charging conductor for hydraulic fracture diagnostics

Hydraulic fracturing is a key technology for oil and gas production and energy conversion. To ensure the ideal fracturing operation, real-time monitoring is required. This paper proposes an electromagnetic monitoring method based on underground charging conductor. By this method, electromagnetic waves are directly excited at the fracture initiation site by supplying power to the wellbore, and the electric field changes caused by hydraulic fracturing are observed on the ground. Using the single fracture model, we derive the potential formula of the charging conductor on the ground. Water tank experiments show that this method can measure the potential anomalies before and after the fractures are formed and can show the fracture orientation. We apply this technology to the fracturing monitoring for the hot dry rock in well GR1 and obtain high-precision electromagnetic signals in real time. By the charging conductor model, we calculate the fracture orientation and length, as well as the fracturing fluid diffusion range. We also analyze the influence of different fracturing technologies on fracture development and complexity. This study provides reference for adjusting fracturing parameters, optimizing fracturing scheme and deploying heat exchange wells.

DESIGNING A 34.5 kV DISTRIBUTION NETWORK WITH SUPERCONDUCTORS AND COMPARISON WITH THE EXISTING SYSTEM

Aim: Electrical energy goes through many different stages from its generation to delivery to the end user. In the transmission and distribution processes of the electrical energy, the energy losses may occur. It is essential to seek appropriate solutions to minimise the electrical power losses and to eliminate all parameters that impair the quality of energy so as to help the electrical network system can operate efficiently, economically, reliably and sustainably. In this study, a medium voltage distribution network and of all parameters were modelled and examined in the computer environment. Modelling and analysis processes were done through the DigSilent Power Factory program which can perform power system analyses. Method: The study consists of three stages. In the first stage, Rabak Feeder modelling of Izmit TM and some analyses of this feeder were made in the DigSilent program. In the second stage, all the underground aluminium conductors in Rabak Feeder were replaced with the superconductors and were modelled and analysed in the DigSilent Power Factory program. In the third stage, Rabak Feeder was redesigned with the superconductors and analyses were made. Results: As a result of these analyses, all parameters of the models were examined. The parameters obtained from the existing and the other two-stage models were compared. These comparisons show that the efficiency of the system increases while the voltage drops and energy losses both decrease when the superconductors are used. Conclusion: The use of the superconductors has increased the efficiency of the system by reducing the voltage drops and energy losses.

Bare versus insulated conductors for improving the lightning response of interconnected wind turbine grounding systems

This paper investigates the lightning response of a pair of interconnected wind turbine grounding systems assuming their connection to be performed by a bare or insulated underground conductor. Typical first and subsequent stroke current waveforms are injected at one of the grounding systems and the transient response is studied for different soil resistivities considering frequency-dependent soil parameters. The ground potential rise (GPR) at the current injection point and the voltages transferred to the adjacent grounding system are calculated. GPR peak reductions are obtained using either a bare or insulated conductor, but the former is more effective. It is shown that when the wind turbine grounding systems are interconnected by a bare conductor, the GPR peak reduction is essentially due to the interconnecting wire. On the other hand, when the interconnection is made through an insulated conductor, the GPR reduction is related to the current that is partly diverted to the adjacent tower, especially for high resistivity soils. For an insulated interconnecting conductor and first lightning return-stroke currents, the adjacent grounding system also contributes to the GPR peak decrease.

Characterizations of a Novel Structure of Fault-Tolerant HTS Cable

This paper presents a type of high temperature superconducting (HTS) cable, which is fabricated by winding the second generation (2G) HTS tapes on round former consisting of stranded stainless steel (SS) wires. It has the advantages of strong flexibility, high mechanical strength, and high engineering current density. With taking the resistivity of SS much larger than that of copper or aluminum, the cable has higher resistance and strength than the conventional HTS cable with former made from copper strands at condition of fault accident. After the configuration of the cable is designed in detail, the quenching resistance and fault current limiting are numerically analyzed. We fabricate a model cable and carry out the experiment of fault current. The experimental results show that the quenching resistance of this cable is much higher than the resistance of conventional underground XLPE cable and overhead conductor, which indicates that the proposed cable has a strong ability of fault current limiting and can be applicable in HTS devices with functions of fault current limiting such HTS cable, transformer, motor/generator, and current limiter.

Partial discharge measurement in solid dielectric of H.V Cross-linked polyethylene (XLPE) submarine cable

<p>A partial discharge described as anon-linear electrical break-down even that happened in a section of insulating area between two conduct which are at different potentials the damage of the insulating material, these conductors have a different insulating material potential of damage, under AC voltage discharge interval process. In this paper, we propose a Matlab /Simulation software. A detailed analysis of the partial discharge (PD) signal in the underground electric power conductor performed for monitoring, and investigation of numerous effects associated with the partial discharge event, such as heat ,phonic and electrical. Thus, to gain the important data of the insulating material status.</p>

Of "Sound" and "Unsound" Body and Mind: Reconfiguring the Heroic Portrait of Harriet Tubman

Of "Sound" and "Unsound" Body and MindReconfiguring the Heroic Portrait of Harriet Tubman Janell Hobson (bio) Harriet Tubman (ca. 1822–1913) is central to narratives of US progressive history and specifically black women's history. For this reason, she can easily be invoked in a historic acceptance speech by Viola Davis, who became the first black woman to win a Leading Actress Emmy in 2015 at a time when she had planned to produce and star in a Tubman biopic. Tubman has also inspired the establishment of a national park, as with the Harriet Tubman Underground Railroad National Monument, and won the popular vote in a 2015 campaign to place a historic woman on the US currency. She is even contemporized for modern audiences, whether that involves denigrating her in a vulgar spoof called the Harriet Tubman Sex Tape, which briefly appeared on and then was subsequently removed from Russell Simmons's All-Def Digital YouTube channel due to its controversy, or celebrating her in a satirized Drunk History episode on Comedy Central, as portrayed by Octavia Spencer. She also appeared in the popular television series Underground, portrayed by Aisha Hinds, who delivered an unforgettable monologue in her iconic role. Functioning as perhaps the most iconic black woman in American culture, Tubman's image, words, and story continue to inspire and provoke. Despite her hypervisibility as a historic icon, Tubman, who is renowned for her status as an Underground Railroad conductor, Civil War hero, and woman's suffragist, remains invisible as a person with a disability. That is, her disability as an identity marker is downplayed. I raise this issue for a few reasons. First, Harriet Tubman has been heralded as an extraordinary individual with incredible strength resulting in self-liberation and the liberation of approximately seventy slaves from the antebellum South on the Underground Railroad, and yet her "superwoman" abilities remain a mystery for many—mostly because these abilities remove her from the realm of the ordinary and the everyday. Second, this image of strong black womanhood clings to a woman who historically suffered from a disability [End Page 193] throughout her life, thus complicating the "strength" she embodied. Finally, Tubman was perceived as "illiterate," a woman who could not read nor write and therefore lacked the literary agency to make her own story legible in the annals of history. This last point shifts the critique of Tubman's disability from the physical to the cognitive, in which her ingenuity, navigational skills, and survival techniques are rendered mystically, even magically, as if they could not be based in intellectual genius. Steeped in romanticism and mysticism—guided as she was by her "supernatural" visions in her journey along the Underground Railroad—Tubman also functions as more mythical than historical in the popular imaginary. She becomes what Vivian May describes as an "icon of strength," someone who "seems ahistorical, selfless, and without equal, not someone who worked within long-established networks of communication and resistance."1 Such a mythic lens further restricts and confines notions of heroism. Tubman's history is much like that of other legendary historical figures, who represent what Nell Painter calls "invented greats."2 Utilizing the example of Sojourner Truth (1797–1883), another black woman icon, Painter argues that such "invented greats" are "consumed as a signifier and beloved for what we need [them to be]."3 If greatness is based on what we need our icons to be, then perhaps it is time to redefine what it means to be "great." In other words, a non-ableist rendering of the "great woman" must reconstitute Tubman in a way that foregrounds what we might consider to be her "vulnerable strength" in the historical narrative. By complicating her strength through the lens of vulnerability, I in no way wish to diminish her abilities or to engender an ableist critique of the strength she embodied. Instead, I wish to call attention to the ways that we have discursively distinguished between weakness and strength, in which the superwoman is always capable, while her opposite—the disabled woman—is often assumed to be incapable. This is a supposition that writer Carolyn Tyjewski challenges when reminding us that "if one looks...

A Noniterative Approximation of a Full-Wave Model of Thin Wire Above and Buried in a Lossy Ground

This work proposes a formulation to overcome some of the numerical challenges of a full-wave model of a lossy single-phase overhead line or a bare underground conductor without significant loss of accuracy. This approach is defined as a quasi full-wave approximation which consists to a non-iterative approach to avoid solving the integral equation associated with a full-wave model. For the sake of comparison, four possibilities are considered in the evaluation, namely: full-wave, quasi-full-wave, quasi-transverse-electromagnetic and image approximations. The results show that the loss of information of the proposal approach is minimal and it can be used for a suitable evaluation of the electromagnetic fields associated with the overhead line or buried conductor.

Arrangement Optimization of Power Cables in Harmonic Currents to Achieve the Maximum Ampacity Using ICA

In this article, a new electro-thermal optimization algorithm is proposed to determine the parallel power cables arrangement to obtain the maximum ampacity. The optimization procedure is based on the imperialist competitive algorithm (ICA). Electrical calculations are performed using the sub-conductors method and consideration of the skin and proximity effects. FEM thermal model and electrical calculations are coupled with optimization procedure to determine the ampacity in the optimization algorithm. Optimized arrangements are determined under sinusoidal and harmonic load currents conditions. Furthermore, the effects of different boundary conditions of the ground surface such as isothermal and convective heat flux are evaluated. The underground single conductor cables with solid bonded metallic sheaths and existing of circulating currents are considered. Cables are considered to be installed adjacent to each other in different rows above each other in flat formations. Also, the artificial bee colony (ABC) optimization algorithm is performed to validate the ICA procedure. Experimental measurement of a case study is carried out for simulation confirmation and the results show good agreement.

Derivative Method Based Orientation Detection of Substation Grounding Grid

The grounding grid is a key part of substation protection, which provides safety to personnel and equipment under normal as well as fault conditions. Currently, the topology of a grounding grid is determined by assuming that its orientation is parallel to the plane of earth. However, in practical scenarios, the assumed orientation may not coincide with the actual orientation of the grounding grid. Hence, currently employed methods for topology detection fails to produce the desired results. Therefore, accurate detection of grounding grid orientation is mandatory for measuring its topology accurately. In this paper, we propose a derivative method for orientation detection of grounding grid in high voltage substations. The proposed method is applicable to both equally and unequally spaced grounding grids. Furthermore, our method can also determine the orientation of grounding grid in the challenging case when a diagonal branch is present in the mesh. The proposed method is based on the fact that the distribution of magnetic flux density is perpendicular to the surface of the earth when a current is injected into the grid through a vertical conductor. Taking the third order derivative of the magnetic flux density, the main peak coinciding with the position of underground conductor is accurately obtained. Thus, the main peak describes the orientation of buried conductor of grounding grid. Simulations are performed using Comsol Multiphysics 5.0 to demonstrate the accuracy of the proposed method. Our results demonstrate that the proposed method calculate the orientation of grounding grid with high accuracy. We also investigate the effect of varying critical parameters of our method.

Frequency-dependent models of overhead power lines for steady-state harmonic analysis: Model derivation, evaluation and practical applications

This paper presents a novel frequency-dependent model for electric power lines to be used in harmonic studies. First, the differential equations representing the distributed nature of the line electrical parameters are considered; frequency dependency due to the effect of ground return and the skin effect is then incorporated. These derived equations represent what in this paper is defined as the analytical model, used as benchmark for model comparison. The vector fitting technique is used here to approximate the analytical model and derive a frequency-dependent frequency domain model. A passive circuit realization of the proposed model in a PI structure is presented and can be directly implemented in steady-state analysis tools such as harmonic power flow solvers. This paper then presents the evaluation and verification of the proposed model for multiple test cases. The test cases of unbalanced three-phase lines for overhead and underground conductors are considered. Moreover, to evaluate system-level impacts of the proposed model, the IEEE 13 node test feeder is considered. Through the evaluation of the test results, it is shown that the proposed model is more accurate than currently-used steady state models such as the simple (nominal) PI or the constant PI (with constant parameters calculated at fundamental frequency) models in terms of steady state harmonic voltages and currents at the line terminals. Test results obtained using the proposed model are within comparable accuracy to the ones obtained using the electromagnetic and transient (EMT) model, without having to run computationally expensive time domain simulations.

High-Melting Point Asphalt on the basis of High-Paraffin Oil Tar

Objectives: A special place among oil bitumen is occupied by refractory bitumen - bitumen of solid marks or, as they are called, solid bitumen. Methods: They differ from the liquid bitumen with high softening point and some other physical and chemical properties, conditioned by the technological mode of production. Bitumen of solid brands find their application in various sectors of the economy both in pure form, as the basic raw material, or as a mixture with various organic products and minerals as part of the production of a number of technical materials. Results: The positive qualities of refractory bitumen and asphaltites, making them indispensable for heat and water proofing of underground channel-free heat conductors are: high softening point; thermo plasticity, which excludes the appearance of cracks; watertight; low water absorption (up to 30 times less than bitumen perlite). The possibility of obtaining high-melting grades of bitumen from high-paraffin tar in the presence of a catalytic complex by “conventional oxidation” that is the raw material purge air, and without purging air using potassium permanganate as a source of molecular oxygen. It is shown that in “conventional oxidation” (sparing of oxygen of air) in the presence of a catalyst complex it is possible to achieve a high softening temperature - over 1000C - almost four times faster than using air purging without purging catalyst. Applications: Using the catalyst of atomic oxidation of petroleum residues showed that it took about 7 hours to reach the softening temperature of almost 1300C

Making Freedom: The Underground Railroad and the Politics of Slavery by R. J. M. Blackett (review)

Reviewed by: Making Freedom: The Underground Railroad and the Politics of Slavery by R. J. M. Blackett Christopher Leadingham Making Freedom: The Underground Railroad and the Politics of Slavery. By R. J. M. Blackett. (Chapel Hill: The University of North Carolina Press, 2013. Pp. ix, 102.) Underground Railroad (UGRR) stationmasters, stockholders, and conductors assisted in the escape of thousands of runaway slaves through much of the nineteenth century. Early histories of the movement, typically written by the descendants of white abolitionists, largely denied agency to both the free and enslaved African Americans who played integral roles in planning and orchestrating escapes. R. J. M. Blackett echoes the work of recent UGRR historians, such as Keith Griffler, to contest this view and demonstrate black agency. He also examines the passage of the 1850 Fugitive Slave Law and explains that the legislation shaped the political milieu of the period. The author illustrates how the actions of black and white abolitionists, escaped slaves, and southern lawmakers influenced local, state, and federal policies and shaped the future of both slavery and the national government. Blackett employs vivid examples from the Ohio Valley to demonstrate that the slaves themselves were motivated to escape based upon innate notions of freedom. Those who chose to self-emancipate did so for a variety of reasons. Some hoped to be reunited with family members and friends. Others chose to leave when masters violated informal hiring agreements. The more opportunistic, such as fifteen-year-old Zechariah Mead, followed the example of others and escaped as members of large groups. The author explains that the promise of freedom and the proximity of free land motivated many to forsake the bonds of servitude. Slaveholders sought to limit both the spread of news and the mobility of slaves by passing legislation that prohibited bondsmen from comingling with working-class whites and free blacks. Slaves often devised and coordinated their own escapes. Some that escaped utilized the federal postal system to communicate with and arrange for the passage of family members and friends. Abolitionists such as William Still of the Philadelphia Vigilance Committee played key roles in relaying information to those left behind. Blackett maintains that the passage of the 1850 Fugitive Slave Law thrust the actions of escapees and those who aided them into the public spotlight. The legislation, a component of the Compromise of 1850, made the recapture and rendition of slaves a national matter. Extensive resistance to the law amplified sectional tensions and encompassed the larger debates concerning slavery and the unity of the national government. Free-born African Americans and their white northern allies united to oppose the law and assist fugitive slaves in their pursuit of freedom. Some in Harrisburg, Pennsylvania, launched a committee to aid escapees as they passed through the city. The author demonstrates that the enactment of the Fugitive Slave Law led to a rash of kidnappings across [End Page 90] southeastern Pennsylvania that heightened tensions between the Pennsylvania and Maryland state governments. Public opinion widely favored the continued enforcement of the law and the legislation proposed in the Pennsylvania legislature sent a clear message that runaways were not welcome in the state. Escapes highlighted the vulnerability of the slave system. Southern slaveholders were skeptical that slaves acted on their own behalf. Local and regional newspapers hastily drew links between escapees and those free blacks and whites suspected of harboring abolitionist sentiment. Blackett demonstrates that such connections were not so farfetched. Northern abolitionists frequently traveled south under the guise of legitimate business ventures to help fugitive slaves escape from the region. Their actions created much suspicion among slaveholders and heightened the ambiguity of the UGRR. The author explains that some slave masters created defensive organizations to stem the tide of slave escapes. In Kentucky, slaveholders from Boone, Mason, Pendleton, and Bracken Counties gathered in November 1852 to inventory members’ slaves and establish a recapture fund. Others called for a boycott of all northern manufactures and even considered the expulsion of free blacks from the South. However, southerners proved unable to stem the tide of slave escapes despite their best efforts. R. J. M. Blackett effectively illustrates the powerful social and political transformations wrought by the 1850...

High-order fast integration for earth-return impedance between underground and overhead conductors in Matlab

Purpose – The earth-return mutual impedances between underground and overhead conductors can be expressed by Pollaczek integrals. Many efforts have been exerted to calculating this kind of integrals. However, most of numerical methods turn out to be time-consuming as integrands become highly oscillatory and strongly singular. Therefore, efficient algorithms should be devised. The paper aims to discuss these issues. Design/methodology/approach – The paper separates the singularity from the whole integral and couple with the singularity and oscillation, respectively. A sinh transformation is applied for the finite part and complex integration method is used to calculate the tail. Findings – Numerical experiments show that the given method shares the property that the stronger the singularity and the higher the oscillation, the better the accuracy of the calculation. Originality/value – The sinh transformation is first proposed to calculate Pollaczek integrals. This efficient algorithm can be used to evaluate mutual impedances between conductors. Also, it provides a new aspect of the research on fast calculation of Pollaczek integrals and Sommerfeld integrals.

Electric Transmission: Underground HVDC Supergrid Can Work in Europe

AbstractElpipes are game‐changing underground high‐voltage DC (HVDC) power lines that will allow pipeline companies to compete in the power transmission market. Elpipe technology uses polymer‐insulated underground HVDC conductors that are rigid (not wires, but sections of bus pipe). This allows much heavier conductors than are possible if they have to wrap on a reel. This greater capability means that they can carry more than twice as much power (more than 15 gigawatts) as the largest transmission line ever built, a 7.2‐gigawatt, 800‐thousand‐volt overhead HVDC line in China built by ABB and State Grid Corp China.

Efficient methods for the computation of Pollaczek integrals in the magnetic field

Calculation of the Pollaczek integral is very important in evaluating the magnetic field in air generated by an underground conductor. This paper provides an efficient algorithm to calculate these integrals by splitting the semi-infinite range into two parts, where the integral tail is evaluated by complex integration methods, and the integral on the finite segment is calculated by the Clenshaw-Curtis quadrature. The computational cost remains the same regardless the frequency, and the higher the oscillation the better the accuracy of the calculation. The efficiency and accuracy are tested by numerical examples.

Exact Solution of Pollaczek's Integral for Evaluation of Earth-Return Impedance for Underground Conductors

Calculation of earth-return impedance for underground conductors is based on the efficient evaluation of Pollaczek's integral. So far, the established practice involved either approximate expressions or numerical integration algorithms. Apart from extensive comments on the latter, this paper presents for the first time three exact solutions in the form of converging series. One of the series guarantees a specific relative accuracy for any parameter range with a specific number of terms and can be regarded as the definite solution that will hopefully settle the issue of computing Pollaczek's integral both rapidly and accurately. The exact solution provides the means to assess the validity of the impedance formula.

The Research of Borehole-Ground DC Method Detecting Anomaly of Underground Dynamic High-Resistivity Conductor and Case Hole Effect

In exploration of coalbed methane, the release and accumulation of absorbed gas driven by underground water is equal to existence of high-resistivity conductor. Application of numerical modeling conducted with finite difference to analyze anomaly sounding corresponding to underground high-resistivity conductor in borehole-ground DC method, and research of casing effect for DC method combining with physical modeling, may attribute to development of borehole-ground DC method which is capable for exploration of coalbed methane.

Calculation of the Magnetic Field in Air Produced by the Underground Conductor Using Pollaczek Integral

A fast approach for evaluating the magnetic field in air generated by an underground conductor is proposed in this paper. By means of the asymptotic extraction technique, the magnetic field can be decomposed into two parts. One is the contribution from the asymptotic integrand, which can be calculated analytically; and the other can be expressed by a sum of the definite integral and the exponential integrals. Due to the fact that there is no improper integral involved, the approach proposed here is highly efficient. Meanwhile, the impact of the eddy current to the magnetic field is quantitatively analyzed. The proposed approach could be used in the electromagnetic environment assessment for underground power cable systems.

Fast and Highly Accurate Algorithm for Calculating the Earth-Return Impedance of Underground Conductors

The earth-return impedance of underground conductors, whose expression was first derived by Pollaczek, is of particular importance for the study of the electromagnetic compatibility problems among the underground conductor system. In this paper, a fast and highly accurate algorithm is presented to calculate the Pollaczek's integral. The high accuracy acquired by the proposed procedure is due to the fact that the tail of the Pollaczek's integral is approximated by a sum of several exponential integrals, which in nature means that there is no truncation to the Pollaczek integral. The extensive comparison with published data indicates that the proposed algorithm is highly accurate and the computational time is reasonable.