Class Cables Research Articles

Fire Retardancy Analysis of the Aged Cables in Nuclear Power Plants: Flammability Modelling using Thermogravimetric Analysis and Differential Scanning Calorimetry

The first step towards fire protection in nuclear power plants based on the concept of ‘Defense in-depth’ is realized through the minimization of combustibles. Regarding the realistic methods for minimizing combustibles in nuclear power plants, the fire retardancy of cables as the highest number of combustibles should be kept for design lifetime as well as at construction. The flame test, according to IEEE-383 and IEEE-1202, was conducted to assess the fire retardancy of aged and unaged cables, both of 1E and non-1E classes. However, previous editions of IEEE-383 (such as the 2015 edition) did not require non-1E class cables to be fire retardant. Therefore, a method to validate the fire retardancy of non-1E class cables installed in nuclear power plants (that had) got the construction permission before 2015 should be developed and implemented. Additionally, it is still unclear as to how the accelerated thermal aging specified in IEEE-383 is close to that of the real aged cables in nuclear power plants. Therefore, flammability modelling using thermogravimetric analysis and differential scanning calorimetry is proposed for solving the above mentioned issues and comprehending the flammability of cables beyond the test codes such as IEEE-1202.

Wireless partial discharge tracking on cross-linked polyethylene MV and HV cables

Medium voltage (MV)/high voltage (HV) cable lines are high-value assets and require substantial costs for their installation or replacement. For this reason, the capability to assess the condition of cable lengths and accessories on site is of great importance. Cross-linked polyethylene (XLPE) insulation is extensively used for MV, HV, and extra-high voltage (EHV) class cables [1] thanks to its excellent voltage-endurance and thermomechanical properties. In particular, XLPE-insulated cables feature substantially lower losses, easier manufacturing and jointing procedures, better environmental compatibility, and higher operating temperature compared with impregnated paper cables, which lead to lower costs in procurement and operation [2], [3].

Development of long-term reliability evaluation method for polypropylene insulated MV cables

Polypropylene (PP) has excellent heat resistant and is an environmental friendly insulation material that can be recycled comparing to cross-linked polyethylene. In Europe, PP insulated high-voltage class cables were commercialised as following the medium-voltage (MV) class. Therefore, authors developed the PP insulated cables and performed thermal, physical, and electrical tests. The most important thing will be to verify the design life of developed cables. The authors developed the long-term reliability evaluation method using frequency acceleration and established a draft standard for PP insulated MV cable.

New HTS Cable Project in Japan: Basic Study on Ground Fault Characteristics of 66-kV Class Cables

In July 2014, a new high-temperature superconducting (HTS) cable project supported by the New Energy and Industrial Technology Development Organization began in Japan. The aim of this project is to verify and improve the safety and reliability of HTS cable systems. The main verification targets are system safety in the event of the following accidents: (1) ground fault; (2) short-circuit current; (3) cryostat failure; (4) a low heat loss cryostat; and (5) a high efficiency cooling system. If a ground fault occurs, it is a matter of concern that the pressure in the cryostat increases due to the arc energy. It is an additional concern if the arc penetrates the cryostat so that the liquid nitrogen leaks out of the cable. It is important to know the amount of energy in the arc in order to numerically predict the outcomes of a ground fault. We performed basic ground fault tests using sheet samples immersed in liquid nitrogen while measuring the arc energy and also examining the structure of a protection layer that can prevent arc penetration to the outside of the cable core.

Influence of a Stainless Steel Core on Coupling Loss, Interstrand Contact Resistance, and Magnetization of an $\hbox{Nb}_{3}\hbox{Sn}$ Rutherford Cable

Calorimetric and magnetic AC loss measurements were made on a pair of TQ (ldquotechnology quadrupolerdquo) class cables, one with and the other without a stainless steel core. The coupling losses are compared to the cables' hysteretic losses determined at the same time; the latter being compared to the magnetically measured hysteretic losses of individual strand segments. The outcomes of these measurements were: (i) the effective interstrand contact resistances of the uncored and cored cables, (ii) their hysteretic losses translated in terms of ldquoeffective, ICRs (interstrand contact resistances)rdquo for comparison with the above, and hence an evaluation of the real effectiveness of the core in a contemporary cable (iii) a comparison of the cable and strand hysteretic losses and hence an estimate of an effective filament diameter, , for the as-cabled strands.

Defect tolerance of solid dielectric transmission class cable

This paper addresses the issue of determining the level of defect that is likely to cause the failure of solid dielectric transmission class cables. It also proposes methods for predicting the level of defect that is likely to cause failure and to provide a simple analytic approximation for doing so in the case of conducting spheroids aligned with the electric field. A common assumption is that conducting particles > 100 /spl mu/m in length are likely to cause failure of extruded dielectric transmission cable. This analysis suggests that when the effects of operation at elevated temperature are included in the analysis, this is probably an appropriate criterion with a sound technical basis. For maximum background fields in the range of 15 kV/mm, as presently seen near the conductor shield of some transmission class cables, a worst-case particle length in the range of 0.1 mm is likely to be required to cause failure for the worst-case local polymer morphology in the range of the maximum operating temperature.

ＣＶケーブル絶縁劣化診断技術

XLPE power cables have been in use for long time now and some of them are approaching 30 years of their designed lifetime. However, under the present severe economic situation, it is necessary to use the existing apparatus as long as possible. So, degradation diagnostic methods with high reliability are needed earnestly. This paper explains the insulation degradation mechanism of XLPE power cables and the newest diagnostic methods on each voltage class. In 3.3-77kV classes, fairly high extents of the cable accidents depend on the water-tree degradation. For 3.3-6.6kV class cables, on-line diagnostic methods with high reliability to detect bridged water-trees have been developed and put in practical use. And, for 22-77kV classes, two promising off-line diagnostic methods to detect un-bridged water-trees have begun to carry out in on-site tests.

Evaluation of jacket materials and configurations and effect of moisture absorbing materials on preventing water tree growth in power cables

Polymer insulated medium voltage cables have experienced premature failures in-service, due in large part to water treeing. Research has shown that the initiation sites of these water trees are often located where there are stress enhancements at the insulation/semiconducting shield interface and where water soluble contaminants permeate into the insulation. Material suppliers, cable manufacturers and users have introduced improved materials and cable designs as well as processing, manufacturing, transport, storage, and installation techniques that minimize contamination. Despite these advancements, gradual contamination can still occur due to the diffusion of ground water into the insulation. In fact, certain contaminants that are carried through the semiconductor/insulation shield interfaces tend to promote water tree growth. Manufacturers are now beginning to recognise this problem and have suggested the use of moisture resistant cables with jackets made of PVC, polyethylene or metal/polymer laminates along with underjacket water absorbing materials. This paper discusses the effectiveness of different jackets and materials and presents data on the effectiveness of water absorbing materials in delaying water permeation into the insulation. A simple and efficient cable-cell technique was developed which monitored the effectiveness of complete cable designs, by measuring the long-term water permeation resistance of short lengths of distribution class cables.

Lifetime assessment by intermittent inspection under the mixture Weibull power law model with application to XLPE cables.

This paper proposes a new treatment for electrical insulation degradation. Some types of insulation which have been used under various circumstances are considered to degrade at various rates in accordance with their stress circumstances. The cross-linked polyethylene (XLPE) insulated cables inspected by major Japanese electric companies clearly indicate such phenomena. By assuming that the inspected specimen is sampled from one of the clustered groups, a mixed degradation model can be constructed. Since the degradation of the insulation under common circumstances is considered to follow a Weibull distribution, a mixture model and a Weibull power law can be combined. This is called The mixture Weibull power law model. By using the maximum likelihood estimation for the newly proposed model to Japanese 22 and 33 kV insulation class cables, they are clustered into a certain number of groups by using the AIC and the generalized likelihood ratio test method. The reliability of the cables at specified years are assessed.

Thermoluminescence in XLPE cable insulation

Crosslinked polyethylene (XLPE) has been employed in underground transmission and distribution cables because of its excellent electrical and mechanical properties, such as low permittivity and dielectric loss, high degree of toughness, and good flexibility. An underground power cable operates at temperatures above ambient and the polymeric insulation is usually crosslinked to provide mechanical strength to withstand the high temperatures. Chemical crosslinking is commonly employed; however, chemical crosslinking creates byproducts such as acetophenone, /spl alpha/-methylene styrene, and cumyl alcohol. The general practice is to decrease the concentration of the volatile crosslinking byproducts from the newly manufactured transmission class cables before they are commissioned into service. The concentration of the byproducts is decreased by treating the cables at a high temperature in a vacuum oven. At present, to determine the residual concentration of the byproducts, the treatment has to be stopped, a sample of the polymer has to be cut from the treated cable and the byproducts have to be extracted for several hours from the polymer before they can be analyzed. This paper describes a novel, non-destructive optical method for determining the concentration of the byproducts in XLPE prior to cable installation. The method involves in situ detection and measurement of thermoluminescence emitted by the crosslinking byproducts during the pretreatment of the cable, It is shown that the measurement of the intensity of thermoluminescence provides a direct indication of the concentration of the byproducts and that it is more sensitive than mass spectrometry.

Performance characteristics of XLPE versus EPR as insulation for high voltage cables

The physical and electrical properties of crosslinked polyethylene (XLPE) and ethylene propylene rubber (EPR) are compared in the context of their use in transmission class cables. Results indicate that the 138-kV XLPE cable has AC withstand/breakdown strength at least 25% higher than the 150-kV EPR cable. The XLPE cable exhibits about 70% higher impulse strength than the EPR cable. The loss factor of the XLPE cable is at least 20 times lower than that of EPR cable. Thus with XLPE cables, the yearly energy savings can be on the order of 15 MWh/cct. km for a 69-kV system, 52 MWh/cct. km for a 138-kV system and 127 MHh/cct. km for a 230-kV system.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Instability in kiloamp class a.c. superconducting cables

In kiloamp (kA) class superconducting cables for a.c. use, where each strand does not have an insulation layer, the quench current in 60 Hz operation was found to be no more than 50% of the d.c. critical current, even on the load line. The degradation in the 60 Hz quench current of the kA class cables is discussed with respect to: 1, an a.c. instability in the multifilamentary wire; 2, magnetic coupling among strands in concentric multistrand cables; 3, the influence of local disorder in cabling on current distribution; and 4, the temperature rise due to steady a.c. losses. While points 2 and 3 induce non-uniform current distribution, points 1 and 4 were found to be factors in the reduction of quench current in the strands with higher current density. Some local overheatings may also contribute to the intense degradation.

Temperature Rise of Submarine Cable on Riser Poles

Results of outdoor temperature-rise tests on submarine power cables installed under guards on riser pole are presented. Test data were used to determine ampacities for three steel-wire armored distribution class cables under specific solar radiation conditions. The measured data also compared well with results from an existing cable ampacity computer program. Some discrepancies, however, indicated that the program predictions could be improved if eddy-current and hysteresis losses were considered in the calculation method used for single-phase cables on riser poles. For a valid comparison between measurements and calculations, it was necessary to account for limitations in the existing computation method by conditioning some program inputs. Consequently, a technique was developed for deriving a single-valued program input that would represent the effect of time-varying solar radiation. A thermal circuit used to determine the transient response of the cable/guard system is presented, along with values for the thermal parameters of three submarine cables. A revised method used to calculate the external heat dissipation coefficient for vertical cable guards is also described. >

Temperature rise of submarine cable on riser poles

Results of outdoor temperature-rise tests on submarine power cables installed under guards on riser pole are presented. Test data were used to determine ampacities for three steel-wire armored distribution class cables under specific solar radiation conditions. The measured data also compared well with results from an existing cable ampacity computer program. Some discrepancies, however, indicated that the program predictions could be improved if eddy-current and hysteresis losses were considered in the calculation method used for single-phase cables on riser poles. For a valid comparison between measurements and calculations, it was necessary to account for limitations in the existing computation method by conditioning some program inputs. Consequently, a technique was developed for deriving a single-valued program input that would represent the effect of time-varying solar radiation. A thermal circuit used to determine the transient response of the cable/guard system is presented, along with values for the thermal parameters of three submarine cables. A revised method used to calculate the external heat dissipation coefficient for vertical cable guards is also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Innovative simplicity brought to polymeric transmission cable joints

Heat-shrinkable materials have become widely established as a way of providing joints and termination for distribution class cables. The technology has been extended to develop a joint for 69 kV cables. Simple components and a special connector were developed to create a slim profile joint that is easy to install. The design overcomes some problem areas for polymeric cables-water ingress, insulation shrink back, and conformance to the cable substrate. Although under revision, IEEE 404-1986, the specification for cable joints, does not currently apply to 69 kV products. A test regime was devised by examining relevant test criteria from other available specifications. Extensive testing has been carried out on the basis of these requirements. Installation and service experience are also described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>