Cable Depth Research Articles

Modeling Magnetic Fields from a DC Power Cable Buried Beneath San Francisco Bay Based on Empirical Measurements.

The Trans Bay Cable (TBC) is a ±200-kilovolt (kV), 400 MW 85-km long High Voltage Direct Current (DC) buried transmission line linking Pittsburg, CA with San Francisco, CA (SF) beneath the San Francisco Estuary. The TBC runs parallel to the migratory route of various marine species, including green sturgeon, Chinook salmon, and steelhead trout. In July and August 2014, an extensive series of magnetic field measurements were taken using a pair of submerged Geometrics magnetometers towed behind a survey vessel in four locations in the San Francisco estuary along profiles that cross the cable’s path; these included the San Francisco-Oakland Bay Bridge (BB), the Richmond-San Rafael Bridge (RSR), the Benicia-Martinez Bridge (Ben) and an area in San Pablo Bay (SP) in which a bridge is not present. In this paper, we apply basic formulas that ideally describe the magnetic field from a DC cable summed vectorially with the background geomagnetic field (in the absence of other sources that would perturb the ambient field) to derive characteristics of the cable that are otherwise not immediately observable. Magnetic field profiles from measurements taken along 170 survey lines were inspected visually for evidence of a distinct pattern representing the presence of the cable. Many profiles were dominated by field distortions unrelated to the cable caused by bridge structures or other submerged objects, and the cable’s contribution to the field was not detectable. BB, with 40 of the survey lines, did not yield usable data for these reasons. The unrelated anomalies could be up to 100 times greater than those from the cable. In total, discernible magnetic field profiles measured from 76 survey lines were regressed against the equations, representing eight days of measurement. The modeled field anomalies due to the cable (the difference between the maximum and minimum field along the survey line at the cable crossing) were virtually identical to the measured values. The modeling yielded a pooled cable depth below the bay floor of 2.06 m (±1.46 std dev), and estimated the angle to the horizontal of the imaginary line connecting the cross-sectional center of the cable’s two conductors (0.1143 m apart) as 178.9° ±61.9° (std dev) for Ben, 78.6°±37.0° (std dev) for RSR, and 139.9°±27.4° (std dev) for SP. The mean of the eight daily average currents derived from the regressions was 986 ±185 amperes (A) (std dev), as compared to 722 ±95 A (std dev) provided by Trans Bay Cable LLC. Overall, the regressions based on fundamental principles (Biot Savart law) and the vectorial summation of cable and geomagnetic fields provide estimates of cable characteristics consistent with plausible expectations.

Analysis of underground cable ampacity considering non-uniform soil temperature distributions

An analytical model for the assessment of cable ampacity due to non-uniform underground temperature distribution is presented. The uneven underground temperature is usually caused by a non-uniform surface heating (e.g., a street or parking crossing, etc.), which is extended for certain length along the cable installation and in depth. The underground temperature distribution is obtained by solving the heat equation with the respective boundary conditions. The cable ampacity reduction is calculated as a function of the surface temperature distribution and the cable depth of burial. The model is validated and several numerical results are obtained for different installation conditions.

Tension Analysis of Submarine Cables during Laying Operations

This paper presents a semi-analytical approximation for a two-dimensional (2D) tension analysis of submarine cables during laying operations. In the analysis, based on geometric compatibility relations and equilibrium equations, a set of non-linear differential equations are obtained. The present model considers effects of ocean currents, cable ship motion, pay-out rate, water depth and material properties on submarine cable behavior in water, which are crucial during laying operations. As shown in numerical examples, with consideration of currents and cable ship motion, the cable tension appears to be smaller and cable configuration curve tends to be fatter than the conventional catenary theory.

Effect of the transmission configuration of wind farms on their capacity factors

This study conducted a feasibility study to analyze and improve the operational performance of two current onshore wind farms on the Changhua coastal area in Taiwan. We selected two adjacent wind farms A and B with similar wind-power density and geographical conditions; whereas, their main differences were the material of cables, the type of transformers, the number of cable branches, and the depth of buried cables. In actual operation states, the wind farm A had greater capacity factor than the wind farm B; therefore, the wind farm A was regarded as a base case, and two new wind farms 1B and 2B, resulting from the changes in the cable materials, transformer types, cable branches, and buried cable depth of the wind farm B, were proposed to assess the feasibility of system improvement. Results showed that the material of cables, the type of transformers, the number of cable branches, and the depth of buried cables were the crucial factors of affecting the efficiency of wind farm B. Shallow cabling increased the temperature of cables, higher temperature causing a decline in cable capacity, and this phenomenon was crucial to aluminum cables rather than copper cables. The results of comparing the wind farms 2B with B indicated that the maximal transmission loss of cables was reduced by 6.4GWh/year, and the maximal annual CO2 emission was reduced by 4.5kt/year. Additionally, the increased cost of transformers and cabling was recovered in 2.12years, when the wind farm B was modified to 2B before construction.

Root temperature and energy consumption at different cable depths in electrically heated substrates

A finite element method-based model of a substrate heated by an electric heating cable buried in a thermal isolated container was experimentally validated with root mean square error values of root zone temperature ranging 0.25 to 0.62 oC. The two-dimensional transient model allowed variations in the physical properties of the substrate with temperature, water content and depth. The operation of nine configurations of a heating cable buried in sand at different depths (50 to 450 mm, at 50 mm intervals) at 200 mm spacing was simulated and assessed. The validated model was used to perform 24-h simulations applying boundary conditions, and substrate moisture content was experimentally obtained at a mean substrate surface temperature of 13.98 oC. Such simulations reproduced the operation of the heating system by setting a reference temperature of 20 oC at the control point in the root zone. Burying the heating cable in the surface layers of the substrate caused large temperature gradients and high heat losses through the substrate surface. Accordingly, average temperature in the root zone increased with heating cable depth, up to the 200 mm depth. For greater depths, temperature in the root zone was constant. The ON/OFF control was most effective with the heating cable buried in the root zone and at control point temperatures of 20 ± 1 oC. Burying the heating cable in the surface layers required higher energy consumption, up to 28 % at 50 mm. The most efficient heating cable depth was 350 mm, with a daily energy consumption of 6750 kJ m-2.

Effect of Dry Zone Formation around Underground Power Cables on Their Ratings

As it is known, there are many factors affecting underground power distribution cables' loadings such as ambient temperature, cable depth laying, number of cable parallel circuits and thermal resistivity of the soil. One important factor usually ignored is the formation of dry zones around the underground power cables due to cable loading. Dry zones usually form around underground power cables under loading condition due to the migration of soil moisture content. In this paper the effect of dry zone formation on the underground power cables ampacity is investigated. De-rating factor for the formation of dry zone around underground power cables is suggested and calculated for different types of natural backfill soils. IEC 60287-1-3 is taken as reference. Experimental work is done to study the dry zone phenomena of each type of soil.

ESTIMATION OF THE ENERGY CONSUMPTION OF ELECTRICAL WIRE HEATING IN SAND SUBSTRATES ACCORDING TO THE TARGET ROOT ZONE TEMPERATURE

Heat transfer processes occurring in greenhouse cultivation substrates are very complex due to the high number of environmental and soil factors involved. Few estimation methods allow establishing the energy consumption of the heating elements as a function of the design parameters (depth and spacing) and of environmental and cultivation criteria, such as the ambient temperature and the target root zone temperature suitable for plant development. The objctive of this work is to analyze the influence of the target root temperature on the energy consumption of six configurations of soil heating system: 150, 225 and 300 mm depth with 100 and 150 mm spacings. An experimental test was arranged to measure ambient and root temperatures and operation times of the electrical heating cables. Dimensional analysis was applied to data obtained experimentally to relate all the involved variables: thermal properties of the substrates, depth, spacing, power and operation time of the heating cable, daily mean values of the measured temperatures. The obtained expressions permitted to quantify the energy consumption. An increase in target temperature in the root zone brings about increases in daily energy demand. An increase in air temperature brings about a decrease in energy requirements, but the slope of the curves increases as a function of target temperature. At a fixed heating cable depth, energy consumption is always higher for 100 mm cable spacing than for 150 mm spacing, and the differences become larger for shallower heating cable installation depths. The heating system with the cable installed at 150 mm spacing and 150 mm depth obtains the lowest energy consumption value, while the configuration with the cable installed at 100 mm spacing and 150 mm depth, and the configurations with the cable buried at 225 mm depth require the highest consumption.

Molecular thermodynamics of water in direct-buried power cables

The balance of this article examines what actually happens to water within a direct-buried cable throughout the day and year as the cable temperature, the soil temperature, the water content of the soil vary. Water, which is almost present at 100% relative humidity at the typical 1 meter burial depth of direct-buried power cables, moves very quickly through any polymeric layers

Ampacity Derating Factors for Cables Buried in Short Segments of Conduit

Buried cables are often routed through short segments of conduit, and when this situation occurs, the ampacity must be reduced or the cable will overheat as a result of the high thermal resistance created at the location of the conduit. This problem is examined for extruded cables by using a finite element heat transfer software program to determine the derating in ampacity that cables in conduits must experience in order to remain below a maximum conductor temperature. The derating factors are provided as a function of conduit length, soil resistivity, burial depth and number of cables in the conduit. The results show that once the length of conduit exceeds about 20 times its outer diameter, then the ampacity of the circuit must be reduced to the value that it would have if the entire length were buried in the conduit. Factors that result in lower cable ampacities, such as high soil thermal resistivity and deeper burial depths lead to larger derating factors.

Modelling and Control of Towed Marine Seismic Streamer Cables

Summary Full-scale measurement data have revealed that slowly varying fluctuations in the course of survey vessels performing marine seismic data acquisition with towed recording (streamer) cables are capable of forcing the in-sea hardware in longitudinal and transverse directions. This may give rise to undesired low-frequency oscillations in the depth of streamer cables. The interaction between the transverse and longitudinal motions takes place at the location of the depth-control devices that are mounted along the streamers. A quasi-static model that describes the low-frequency dynamics of streamer cables is proposed for the purpose of controller design and analysis. The simulation study showed that the overall depth-control performance is sensitive to appropriate tuning of controller gains, selection of sampling period and application of dead bands. A successful depth control will rely on the number and lift capability of the mounted depth-control devices.

Cable Tracking Requirements in the New Millennium

The beginning of the new millennium marks a turning point in requirements for submarine fiberoptic cable location and tracking, brought about primarily by the increasing number of cable networks laid along coastal margins and continental shelves as opposed to direct intercontinental connections over deep ocean basins. This change will result in significantly greater percentages of total cable lengths that will require burial and will also result in a substantial fraction of buried lengths beyond maximum practical range of shore-induced a.c. tones. In addition, the recent and projected increases in bandwidth and volume make lost revenues due to cable downtime increasingly more costly to cable owners, leading to desirability of increased protection by deeper burial depths out to deeper water depths. In this paper, the physical limitations of various techniques for locating, tracking and determining the burial depth of cables powered and unpowered are discussed, and strategies for meeting the requirements posed for the new millennium are considered.

Method for rating power cables buried in surface troughs

An alternative method is detailed by which the ambient temperature parameter as applied to the calculation of ratings of cables buried in surface trough installations can be determined. Improvement in the accuracy of cable rating calculations will allow greater utilisation of the cable asset and assist for example in the planning of system outages for maintenance work. The proposed model calculates the temperature at the cable burial depth based on measurements of solar radiation, windspeed and air temperature. The model is based on physical laws rather than empirical approaches that have been shown to be generally conservative in application. Results based on weather data monitored over a two-year period show that the ambient temperature of the soil at cable depth can be accurately determined and the model provides a significant improvement on existing methods.

Waveform Inversion of Reflection Seismic Data for Kinematic Parameters by Local Optimization

A reformulation of the usual least-squares waveform inversion problem is proposed to retrieve, from seismic data, the kinematic parameters (the two-dimensional (2D) background velocity and the source and cable depth) by local optimization. These last parameters are of paramount importance for a successful inversion of very high resolution (VHR) seismic data which we are interested in. In our inversion the source and cable depth parameters are treated in the same way as the background velocity. To avoid the problem of local minima, a change of unknowns is performed: the depth reflectivity is replaced by its dual variable, called the time reflectivity. In this way, the current value of the reflectivity is stored in the time domain and is strongly decoupled from the current value of the velocity field and cable depth. The increase in modeling complexity (an additional prestackmigration is required for each function evaluation) is compensated by the enlargement of the attraction domain of the global minimum which allows the use of a local optimization technique. A numerical implementation with Born approximation and ray tracing is detailed, in which the derivatives of the travel time are computed via an adjoint state technique for more efficiency. Numerical results illustrate the behavior of the new objective function, and inversion of synthetic and real VHR data for kinematic parameters is performed.

Ampacity of cables in single covered trays

A mathematical thermal model is developed to predict the operating temperatures of cables in a single covered tray when there is load diversity in the power cable bundle. The model accommodates two different loading scenarios: one in which the heat is distributed evenly across the cable tray cross section; and one which concentrates the heavily loaded cables along the centerline, while surrounding them with more lightly loaded cables. The temperature predictions provided by the model are compared to data found in other IEEE papers, data collected in laboratory measurements, and new data from a four-year study of cable trays in an operating nuclear plant. Reasons for differences between the field data and the computer results are discussed. The model is used to evaluate the conservatism in the available Codes and Standards. A derating factor is introduced that is defined in terms of the ampacity of power cables in open-top trays. The derating factor accounts for the added thermal resistance present when a cover is placed over the cables, trapping a layer of stagnant air on top of the cable mass. The computer model is then used to predict values for the derating factor as a function of cable depth. The derating factor is shown to be independent of the composition of cables in the tray. The presence of a cover is shown to reduce the ampacity based on an uncovered tray by up to 25 percent depending on the depth of the cables in the tray.

Disturbance effects on soil solution chemistry due to heating cable installation

Installation of heating cables for warming soil was used to evaluate the effect of disturbance on soil solution chemistry within a northern hardwood forest (Adirondack Mountains, New York). Differences in response among treatments suggested the importance of both the depth and timing of cable installation. There were increases (p>0.05) in many solutes within pilot study plots in which “surrogate cable” was installed at 15 cm depth. Most notably, mean nitrate concentrations for the 1st year following disturbance were 744 μeq l-1 at 15 cm depth compared to 7 μeq l-1 for the non-disturbed control. A comparison of pilot plots with 5 cm cable depth and an unheated soil-warming control plot with the same cable disturbance showed that the seasonality of soil disturbance may have a key role in response to disturbance. The soil solution response was diminished if installation occurred during the spring, a period of rapid uptake of nitrogen by vegetation. Mean nitrate concentrations were 176 μeq l-1 for 5-cm pilot plots (installed in fall 1991) versus 6 μeq l-1 for 5-cm, unheated soil-warming control plots (installed in spring 1992). Disturbance effects were attenuated over time and not generally apparent 1 year after installation.

Design and operation of a deep seismic survey in the Tasman Sea Basin

Deep crustal reflections, appearing at two-way times of 6–20 s, are characterised by a low signal-to-noise ratio and a low-frequency content (~ 5–30 Hz). Optimising the visibility of these reflections requires that: 1.(1) the source energy be concentrated in this band;2.(2) the receiver be as long as practically possible;3.(3) the shot spacing be as snail as possible.An airgun array simulation program was used to investigate the effect of operating a 10-gun array at different depths. It predicted that the source energy could be enhanced at low frequencies by running the gun array at depths of up to 25 m, which would improve the signal-to-noise ratio for deep reflectors by a factor of 2 relative to the same array at 7.5 m depth at the expense of some loss of temporal resolution.The receiver length was limited to 4.4 km by the number of cable sections available and the maximum tension allowable in the cable. It was configured as 88 channels of 50 m length. To reduce the shot spacing, minimise the tow noise and reduce tension in the cable, the ship speed was reduced to 4 knots. A cable depth of 20 m was chosen to reduce sea state noise and keep the receiver ghost notch frequency outside the frequency band of interest.A variety of operational problems was encountered. Fish bites holed 50% of the total cable inventory and cable sections were damaged when they sank below their maximum rated depth after being holed. Shot-generated noise was the limiting factor in deep water. Despite these problems, useful data were obtained over the Lord Howe Rise, Dampier Ridge, Gippsland Basin margin and the deep abyssal plain and the survey demonstrated the use of an airgun array tuned for maximum energy.

えい航式漁具の近似計算法に関する研究

In order to determine the depth, tension and configuration of towing cable by simple calcu-lation, the following study was conducted. (1) Experimental verifications of some assumptions which had been used in studies up to this time, 1-5) (2) A comparison between the calculated values based on the theory and experimental values of the water tank, and corrections of the values by an approximate calculation and coefficients based on the results, (3) A computer program for an approximate calculation, (4) A comparison between the calculated values using the personal computer and the observed values with the field experiments. (1) and (2) were reported already in references. Mainly (3) and (4) are studied here. The calculated Values for the towing states by using this program were coincident with the observed values within about ±5% difference.

Sensitivity analysis of modal quantities for underground cables

An accurate mathematical model, which takes into account both earth and conductor-sheath skin effects, is utilised for the computation of the high-frequency modal-attenuation constants and phase velocities of underground cables. The sensitivities of these quantities to cable dimensions, material properties, earth resistivity, spacing between cables, cable depth and frequency are evaluated for a typical underground cable system. The sensitivity analysis makes it possible to establish the effect of each parameter on modal propagation. The method of calculating the sensitivities can easily be extended to a crossbonded cable system provided the equivalent homogeneous parameters of the major section are determined

Signature Processing of North Sea Air-Gun Data: ABSTRACT

Results of development drilling on a North Sea oil field suggested that the actual structure was much more complex than the original interpretation. We present the results of a reprocessing project on selected seismic lines over the structure. The original data were recorded using a variable cable depth and a deep tow hydrophone for the gun signatures. The data were reprocessed using only signature correction to a zero-phase wavelet. However, results obtained at the horizon of interest were still affected by cable ghosts, frequency attenuation within the overlying sediments, and practical constraints on the recording of the source ghost. Because the purpose of the project was to improve delineation of very small faults, we decided to try to improve resolution by applying corrections for these effects. The initial tests were done by designing and applying End_Page 678------------------------------ filters to the signature prior to the design of the wave shaping operators. We used an average cable ghost operator in this run and designed a single operator for each shot to enhance the wavelet in the zone of interest. The results were encouraging, so we decided to try removing residual effects in a separate pass on a trace-by-trace basis after the normal signature correction. The output obtained was disappointing; therefore, we decided to use prefiltering of the signature before operator design on a trace-by-trace basis. This proved to be much less sensitive to noise on the input data and results show the small faults in the oil reservoir. End_of_Article - Last_Page 679------------

Cable depth selector and coil shunt penetrator

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