Unshielded Cables Research Articles

Energization-Status Identification of Three-Phase Three-Core Shielded Distribution Power Cables Based on Non-Destructive Magnetic Field Sensing

Three-phase three-core distribution power cables are widely deployed in power distribution networks and are continually being extended to address the ever-increasing power demand in modern metropolises. Unfortunately, there are high risks for the repair crew to operate on energized distribution power cables, which can cause deadly consequences such as electrocution and explosion. The predominant energization-status identification techniques used today are either destructive or only applicable to un-shielded power cables. Moreover, the background interferences affect the sensing technique reliability. In this paper, we have developed a non-destructive energization-status identification technique to identify energized three-phase three-core distribution power cables by measuring magnetic fields around the cable surface. The analysis shows that the magnetic-field-distribution pattern as a function of azimuth around the cable surface of the energized (current- or voltage-energized) three-phase three-core distribution power cable is distinguishable from the de-energized one. The non-idealities of phase currents and cable geometry were also discussed, and the proposed method still works under these circumstances. The sensing platform for implementing this technique was developed accordingly, consisting of magnetoresistive sensors, a triple-layered magnetic shielding, and a data acquisition system. The technique was demonstrated on a 22-kV three-phase three-core distribution power cable, and the energized status of the cable can be successfully identified. The proposed technique does not damage cable integrity by piercing the cable, or exposing the repair crew to hazardous high-voltage conductors. The platform is easy to operate and it can significantly improve the situational awareness for the repair crew, and enhance the stability of power distribution networks.

THE EVALUATION OF POSSIBILITY OF NORMAL OPERATION OF CABLES BASED ON TWISTED PAIRS WITH PVC JACKET UNDER THE CONDITIONS OF HIGH HUMIDITY AND TEMPERATURE

Introduction. Development of cables for structured cabling systems based on twisted pairs for shipbuilding is carried out in two main directions: increasing the fire safety of cables and increasing the long-term permissible operating temperature by using new, more heat-resistant, electrical insulating materials. Purpose. Substantiation of the possibility of unshielded cables on the basis of unshielded twisted pairs with thermoplastic polyethylene insulation in PVC protective jacket in conditions of high humidity and high operating temperatures on the basis of the results of accelerated aging. Methodology. The cycle of aging under conditions of increased humidity is performed for 336 hours. Then the sample was under natural drying conditions for 1440 hours. Thermal aging in a thermostat at 90 °C was carried out in two stages: first – for 206 hours, the second – for 260 hours. In the initial state and after accelerated aging, measurements of the capacitance and tangent of the dielectric loss angle of all the insulating gaps at frequencies of 100 Hz, 1 and 10 kHz were performed. Results. According to the results of accelerated aging under conditions of high humidity and temperature, it is established that the design of an unshielded cable based on unshielded twisted pairs with thermoplastic polyethylene insulation in a protective coating based on PVC-plastic is resistant to external influencing factors. Practical value. The prolonged holding at temperature of 90 °C is equivalent to operation at temperature of 40 °C for 6.8 years. At higher operating temperatures, the lifetime of the cable is significantly reduced.

Mitigation of Lightning Flashover from Tree to Medium Voltage Aerial Cable Using Shield Wire

This paper presents the performance and protection of medium-voltage (MV) aerial cables against lightning faults by means of laboratory experiment and digital modeling. With the series of laboratory tests, practical examination of lightning hazard to shielded and unshielded aerial cables is conducted, and the need for shield wire protection is established. For the purpose of simulation studies, digital models are developed by using Alternative Transient Program-Electromagnetic Transient Program (ATP-EMTP) and its transient analysis of control system features. The performance of lightning flashover overvoltage on shielded and unshielded aerial cable is evaluated with the developed digital models. The evaluation is made by considering a direct lightning strike on wooden poles, messenger wires, and nearby trees. Based on the experimental and simulation results, practical recommendations are proposed for improvement in lightning performance of aerial cables. This study offers possible solutions for the protection of aerial cables against lightning flashover, induced overvoltage, and direct lightning strike, which may improve electricity reliability and availability to customers.

Effective filtering solution with low cost small size for common‐mode reduction in dc–dc converters

An effective solution is introduced aimed to reduce the size and cost of electromagnetic interference (EMI) filters in dc–dc converters. This method is based on the insertion of small ground inductor (grounded through RF inductor). This technique is suitable for unshielded cables. The RF inductor prevent the return current of the common-mode (CM) noise at high frequencies, it is inserted between the earth ground (ground reference plane) and the chassis ground of the converter, therefore it isolate the converter chassis from power line ground at high frequencies. As well, maintaining the electrical safety grounding at the power frequency with very low impedance to ground. The efficiency of the proposed method is demonstrated by combining measurements and simulations for the fast testing. The level of CM current is compared versus a specific standard. This allows showing that the EMI emission levels can be reduced by as much as 30 dB.

Power Line Communication Parameters of Multi Conductor Power Line

Abstract: The article describes how to count R, L, C, G parameters of multi conductor overhead lines and cables. Power lines are usually solved as three phase lines, sometimes with neutral line and grounding. For the modelling of these phenomena transmission line model was extended in Franek et al. (2015). But for model usage is necessary to know R, L, C, G parameters of used cables and lines. This article describes how to count these parameters for shielded and unshielded multi conductor cables and overhead lines.

Study on the Cable Crosstalk of Ship Cabin

The mechanism of cable crosstalk involving what and how does the factors affect the level of crosstalk is introduced in detail. A transmission line model for predicting crosstalk between power cable and the other wires nearby with common reference ground based on multiconductor transmission theory (MTL) is developed. Crosstalk among circuit configurations when the victim cables with load terminations are different types is analyzed and simulated. Models where the types of the victim lines are shielded coaxial cable, shielded twisted pair and unshielded twisted pair are simulated. It is found that the shielding can provide an attenuation of about 50dB than the unshielded cables. In addition, the condition of multi-cable coupling is simulated and some thoughts are brought out to inspire more detailed study. Finally, some measures are suggested to suppress the crosstalk between cables according to the two-type of coupling mechanism (inductive coupling and capacitive coupling).

Numerical studies of the electromagnetic reciprocal influences of symmetric communication cable

The reciprocal influences between chains of symmetric communication cables is considered based on mathematical simulations of electromagnetic processes. It is assumed that the electric- and magnetic-field force lines are situated in the plane perpendicular to the cable axis and, therefore, the mathematical models describing the electric-potential distribution and components of the vector magnetic potential of alternating currents in a complex form can be presented in a two-dimensional setting. Differential equations written in the Cartesian coordinate system and describing the electric and magnetic potential distributions are solved by the finite-element method. The electromagnetic processes are studied numerically for the UTP Cat 5e LAN cable used in the structured cable networks. Such an approach allows one to determine electric- and magnetic-field distributions and calculate the coefficients of capacitive and inductive coupling in the cross section of a symmetric cable for a preset position of twisted pairs. The main way to reduce the reciprocal influences in unshielded symmetric communication cables is appropriate selection of twist pitches. The twist pitch in each chain should be chosen such that the integral of the capacitive and inductive coupling coefficients over a length of the symmetry section between all the cable chains tends to zero.

Effect of limiting airflow in mitigating combustion-driven manhole events

"Manhole event" refers to a range of phenomena, such as smokers, fires, and explosions, which occur in underground electrical infrastructure, primarily in large cities. Whereas some manhole events are caused by failure of primary distribution cable, most are caused by failure of unshielded secondary cable in network systems. Based on analysis and knowledge of field conditions, manhole events can be divided into at least two classes, those in which exothermic chemical reactions dominate and those in which electrical energy dominates [4]. In an electrically driven event, the arcing energy is so great that it causes rapid vaporization of the conductor and nearby polymers, which sweeps the oxygen from the cable duct so the event evolves through electrical fault energy induced pyrolysis. In the more common combustion-driven events, the electric fault energy ignites the cable insulation near the fault, resulting in self-sustained combustion as a result of air flowing down the duct. This establishes a combustion zone, which consumes oxygen and liberates heat, causing anaerobic decomposition of polymeric materials downstream of the combustion zone, which results in generation of combustible gases. In combustion-driven manhole events, airflow through the duct plays an important role in the combustion propagation in the duct and the evolution of the manhole event.

Most 50 — Adopted in Asia

With a bit rate of 50 Mbps, MOST 50 Technology not only offers twice the bit rate of the long-established MOST 25 Technology, but also permits the use of unshielded copper cables for networking the MOST devices. The catalyst for Asian manufacturers planning to take MOST 50 onboard was the option of retaining their existing wiring and assembly processes and the lack of requirement to switch to fiber optics. SMSC further compares these two multimedia network standards and conveys possible trends for the various markets.

HF Model of an Unshielded 2-Wire Energy Cable Submitted to Power Electronic Converter Constraints

In adjustable speed drive applications operating at high switching frequencies, common mode and differential mode perturbations may cause premature ageing of electric machines and important electromagnetic radiations. These disturbances are generated by the power electronic converter, but can be amplified by the connection between the converter and the electric machine. This connection is ensured by multi-wire energy cables, shielded or unshielded. Whereas it is easy to find models allowing to simulate the HF behaviour of cables intended to transmit information, the HF models of the cables intended to carry electric power are still to be built.This paper deals with HF modelling of an unshielded 2-wire energy cable, which is a first step to multi-wire cable models. A model with distributed constants is proposed and validated in both time and frequency domains, first in a voltage pulse mode and loaded by a pure resistive load, then in an experimental set-up where the cable ensures the connection between an elementary power electronic converter and a load with inductive couplings and stray capacitors.

An EMC evaluation of the use of unshielded motor cables in AC adjustable speed drive applications

The most common solution for modern adjustable speed drives (ASD) is the use of induction motors (IM) fed by voltage-source inverters (VSI). The inverter generates a pulsewidth modulated (PWM) voltage, with dv/dt values of about 6 kV//spl mu/s or even more. In three-leg inverters for three-phase applications the occurrence of common-mode voltage is inherent due to asymmetrical output pulses. As a result, for electromagnetic compatibility (EMC) reasons, in most applications shielded cables are used between the inverter and the motor, implying high installation costs. The present paper discusses the use of cheaper, unshielded cables from an EMC point-of-view. A new method for measuring electromagnetic interference (EMI) from unshielded cables is proposed and measurement results are presented. The level of EMI is evaluated in different situations: without an output filter, with a classical LC output filter and with an advanced output filter with dc link feedback. It is concluded that, from an EMC point of view, unshielded cables can give very good performance provided that a common-mode (CM) output filter is used.

The Effects of Cable Capacitance on Longwall Power Systems

Utilization voltages used on longwall equipment operating in coal mines in the United States have increased steadily over the past 15 years from 1000 up to 4160 V. This voltage increase has directly influenced the 200% gain in overall longwall productivity from 1987 to the present. The transition from medium voltage (661-1000 V) to high voltage (greater than 1000 V) has permitted significant increases in mining face widths and equipment sizes. Longwall systems with total connected loads of over 5000 hp are now common, and all longwalls in the United States now use high-voltage equipment, with the majority utilizing 4160 V. Shielded cables, which have significantly more capacitance than unshielded cables, are required for high-voltage applications in the mining industry. This capacitance can have detrimental influences on system overvoltages and relay selectivity during ground-fault conditions if the values for the neutral grounding resistor and the ground-fault-relay pickup settings are improperly chosen. These issues are addressed in this paper.

Modeling of magnetic-field coupling with cable bundle harnesses

A field-to-line coupling model is developed for cable bundle harnesses in terms of the scattering currents and total line voltages. The equivalent distributed sources representing the effects of electromagnetic coupling are expressed as a function of the incident magnetic-field components. Such a formulation is particularly suitable to be used for the analysis of multiconductor transmission lines excited by a transient field, when data for the incident electric field are either inaccurate or not available. This model allows the accurate calculation of the induced voltages and currents on complex cable bundles. The effects on the induced voltages and currents due to ground losses and to the presence of the dielectric sheath in shielded and unshielded cables is discussed, considering bundles excited by either slow or fast transient fields. Numerical applications demonstrate the validity of the proposed procedure.

Diagnosis of Rolling-Element Bearings Failure by Localized Electrical Current Between Track Surfaces of Races and Rolling-Elements

The diagnosis and cause analysis of rolling-element bearing failure have been well studied and established in literature. Failure of bearings due to unforeseen causes were reported as: puncturing of bearings insulation; grease deterioration; grease pipe contacting the motor base frame; unshielded instrumentation cable; the bearing operating under the influence of magnetic flux, etc. These causes lead to the passage of electric current through the bearings of motors and alternators and deteriorate them in due course. But, bearing failure due to localized electrical current between track surfaces of races and rolling-elements has not been hitherto diagnosed and analyzed. This paper reports the cause of generation of localized current in presence of shaft voltage. Also, it brings out the developed theoretical model to determine the value of localized current density depending on dimensional parameters, shaft voltage, contact resistance, frequency of rotation of shaft and rolling-elements of a bearing. Furthermore, failure caused by flow of localized current has been experimentally investigated.

A FULLY-AUTOMATED ORCHARD IRRIGATION SYSTEM BASED ON CONTINUOUS MONITORING OF TURGOR POTENTIAL WITH A LEAF SENSOR

A sensor, which continuously monitors leaf thickness in the field with an accuracy of ± 1 micron, was developed and field-tested over a period of six growing seasons. The suitability of three different electrical components was investigated as transducers of linear changes in leaf thickness to a measurable electrical signal. A strain gauge based on a miniature printed circuit of a whetstone bridge fastened integrally to the face of a spring steel blade was found to be sufficiently accurate, able to withstand all ambient weather phenomena and agrotechnical practices, without interrupting normal leaf functions. The simplicity of this configuration makes it easy to install, trouble free with a functional life of at least four years. Notwithstanding the low output intensity of the device, a Campbell CR-10 data logger was able to trigger and read with sufficient accuracy, signals transmitted through standard, unshielded cables from a distance of up to 200 meters. The data logger was programmed to monitor and interpret the data received, and to open and close irrigation valves as a real-time response to leaf thickness variations. It created a high frequency, low volume irrigation regime that reacted to and reduced incipient stress with a resultant reduction of total water application of up to 30%. Concurrent research demonstrate that there is a linear and significant correlation between leaf thickness leaf turgor potential (R 2 >0.9), which in turn has been shown to be an accurate and sensitive measure of plant water status as it affects plant metabolism. The system was tested in commercial plots (citrus: 6 years; avocado: 3 years; cotton: one season) and compared with several variations of standard irrigation regimes. Cropping weights and quality of the sensor-triggered treatments were equal to or better than controlled treatments, but water use efficiency (WUE) was consistently and significantly higher in the sensor treatments.

Performance of Low Output Impedance Composite pH Glass Electrodes

Low output impedance composite pH sensors were constructed by direct attachment of an impedance converter to laboratory purpose combined pH glass electrodes. The signal was transmitted in analog form by unshielded electric cable. The performance of new and aged composite pH sensors was determined by the multiple-point calibration method. In case of new electrodes, the slope and the response time, as well as the reproducibility, were insignificantly influenced by the converter attached (the mean slope values calculated for the six electrode group studied were 57.80 mV/pH for unmodified electrodes and 57.97 mV/pH for modified electrodes). The electrode response was not affected by the presence of various electromagnetic noise sources or by the input impedance value of the measuring instrument. The slope and the response time of aged sensors were considerably improved using the impedance converter. The response time decreased from about 150–180 sec to about 30 sec and the average slope value increased from 5...

Performance of Low Output Impedance Composite pH Glass Electrodes

Low output impedance composite pH sensors were constructed by direct attachment of an impedance converter to laboratory purpose combined pH glass electrodes. The signal was transmitted in analog form by unshielded electric cable. The performance of new and aged composite pH sensors was determined by the multiple-point calibration method. In case of new electrodes, the slope and the response time, as well as the reproducibility, were insignificantly influenced by the converter attached (the mean slope values calculated for the six electrode group studied were 57.80 mV/pH for unmodified electrodes and 57.97 mV/pH for modified electrodes). The electrode response was not affected by the presence of various electromagnetic noise sources or by the input impedance value of the measuring instrument. The slope and the response time of aged sensors were considerably improved using the impedance converter. The response time decreased from about 150–180 sec to about 30 sec and the average slope value increased from 54.94 mV/pH, calculated for unmodified electrodes, to 56.96 mV/pH, for modified electrodes.

On the use of unshielded cables in ionization chamber dosimetry for total-skin electron therapy

The dosimetry of total-skin electron therapy (TSET) usually requires ionization chamber measurements in a large electron beam (up to ). Exposing the chamber's electric cable, its connector and part of the extension cable to the large electron beam will introduce unwanted electronic signals that may lead to inaccurate dosimetry results. While the best strategy to minimize the cable-induced electronic signal is to shield the cables and its connector from the primary electrons, as has been recommended by the AAPM Task Group Report 23 on TSET, cables without additional shielding are often used in TSET dosimetry measurements for logistic reasons, for example when an automatic scanning dosimetry is used. This paper systematically investigates the consequences and the acceptability of using an unshielded cable in ionization chamber dosimetry in a large TSET electron beam. In this paper, we separate cable-induced signals into two types. The type-I signal includes all charges induced which do not change sign upon switching the chamber polarity, and type II includes all those that do. The type-I signal is easily cancelled by the polarity averaging method. The type-II cable-induced signal is independent of the depth of the chamber in a phantom and its magnitude relative to the true signal determines the acceptability of a cable for use under unshielded conditions. Three different cables were evaluated in two different TSET beams in this investigation. For dosimetry near the depth of maximum buildup, the cable-induced dosimetry error was found to be less than 0.2% when the two-polarity averaging technique was applied. At greater depths, the relative dosimetry error was found to increase at a rate approximately equal to the inverse of the electron depth dose. Since the application of the two-polarity averaging technique requires a constant-irradiation condition, it was demonstrated that an additional error of up to 4% could be introduced if the unshielded cable's spatial configuration were altered during the two-polarity measurements. This suggests that automatic scanning systems with unshielded cables should not be used in TSET ionization chamber dosimetry. However, the data did show that an unshielded cable may be used in TSET ionization chamber dosimetry if the size of cable-induced error in a given TSET beam is pre-evaluated and the measurement is carefully conducted. When such an evaluation has not been performed, additional shielding should be applied to the cable being used, making measurements at multiple points difficult.

100BASE-T2: a new standard for 100 Mb/s Ethernet transmission over voice-grade cables

100BASE-T2 is a new physical-layer specification for IEEE 802.3 LANs operating at 100 Mb/s (Fast Ethernet). It enables users of the prevailing 10BASE-T Ethernet LAN technology to upgrade their networks from 10 to 100 Mb/s performance while retaining an existing voice-grade cabling infrastructure. 100BASE-T2 transceivers will operate over two pairs in unshielded twisted-pair cables corresponding to EIA/TIA category 3 (UTP-3), as minimally required for 10BASE-T. In a four-pair UTP-3 cable, simultaneous operation of two 100BASE-T2 links, or one 100BASE-T2 and one 10BASE-T link, is permitted. Since voice-grade cables exhibit more signal attenuation and significantly higher crosstalk coupling between adjacent pairs than data-grade cables, sophisticated digital signal processing techniques are needed to achieve reliable duplex 100 Mb/s transmission over two pairs. The 100BASE-T2 standard defines dual-duplex baseband transmission at a modulation rate of 25 Mbaud. During each modulation interval, a four-bit data nibble or Ethernet-specific control information is encoded into a pair of quinary signals. These signals are transmitted simultaneously on the two wire pairs in both signaling directions. In the receivers, adaptive digital filters are required for echo and NEXT cancellation, equalization, and interference suppression.

Accurate modelling of field stresses in an unshielded three-core power cable

This paper uses the charge simulation technique to calculate the potential and electric field stress distribution at the surfaces of the conductors and the dielectric of an unshielded three-core power cable. The conductors and the sheath are simulated by a suitable finite number of complex line charges. The unshielded three-core cable is placed on a grounded plane and at varying heights above it to calculate the electric field as a function of the height of the insulated cable from the ground. The maximum value of the electric field stress at the grounded plane due to the presence of the insulated three-core cable is detected to check the discharge activities at the grounded plane surface. Comparison is made with field stresses arising from a single-core unshielded insulated cable which are given in the literature. The charge simulation technique is found to be satisfactory to model and calculate accurately the field stresses in a three-core unshielded power cable.