Abstract: In June 2014, the French transmission system operator (Reseau de Transport d'Electricite—RTE) performed a field test on a 64 km 225 kV XLPE underground cable. This paper presents the validation of the cable model from field test measurements. In the first part, the cable impedance and admittance calculations are compared to the per-unit-length parameters evaluated from field test results. In the second part, the field tests are simulated in an Electromagnetic Transients Program (EMTP) to validate the cable model.

Abstract: Very-low-frequency (VLF) high voltage excitation emerges as a promising alternative diagnostic tool to conventional testing at power frequency. In this paper, a comparative analysis of corona discharge in air at power and VLF frequencies is conducted under different levels of voltage excitation. Here, the discharge characteristics are presented in terms of IEC 60270 standardized parameters. Experimental results show that under VLF testing, the discharges exhibit comparatively higher average magnitude, repetition rate per cycle, current and power than testing at power frequency.

Abstract: This paper focuses on the phenomenon of discharge of HVAC cables, which is a concern for utilities when performing AC/DC tests, during maintenance works, and more recently when switching cables for grid voltage control. The study is based on field and laboratory tests of 275 kV pressurized-oil-filled (POF) cables, analytical calculations, and simulations. The contributions of this paper are: field and laboratory measurements of voltages and leakage currents during cable discharge, including a field test carried out in 2015 by the National Grid (UK) on a 275 kV POF cable of 21 km; a method for estimating the leakage resistance and the time required to discharge a cable system using simple parallel RC circuit theory; and typical values of leakage resistance, leakage current, and discharge time for 275 kV cable systems. The influence of temperature, electric field, and humidity on cable discharge is also discussed and a correction factor to account for the impact of humidity is proposed.

Abstract: There are some well-defined guides and standards regarding factory testing of medium voltage shielded cables in laboratories provided by IEEE, IEC, ANSI/ICEA, and CSA. These guides cover AC withstand and PD testing of XLPE and EPR cables and accessories, such as 50/60Hz AC Hipot and PD tests which are routinely conducted on every reel of cable produced at the factory. All terminations, splices, and separable connectors are tested with more or less the same test method using different test levels and timing.

Abstract: Electric cable is an important part of utility power and distribution system. In order to keep the system operation safely and reliable, acceptance testing for cable is necessary not only in-service but also manufacturing process. This paper proposes a novel testing technique which is able to classify the difference between normal and defective low voltage XLPE cable, namely polarization and depolarization current technique (PDC). In this study, PDC testing of low voltage XLPE cable was performed comparatively among five different cases: cable contaminated with a piece of paper, case 2 : cable contaminated with a piece of plastic, case 3 : cable contaminated with grease, case 4 : cable contaminated with a piece of copper, and case 5 : eccentric conductor cable. With environmental control of the testing process, the test results show the polarization current of the defective contaminated cable with copper is higher than that of the regular one, whereas it is lower than that of the defective one with paper, plastic and grease. It is also found that there was indistinctive of PDC in case of copper contaminated and eccentric conductor cable.

Abstract: The continuously increasing installation complexity for medium voltage power cables, results in many weak spots and cable failures due to bad workmanship. This is mainly caused by the large variety of cable accessories as well as the reduction in insulation thickness and therefore in the margin of error throughout the entire cable installation process. The necessity for both commissioning testing of new cables as well as diagnostic measurements as part of a condition based maintenance is just a logical given fact. Nowadays cable testing as well as condition monitoring are well proven measurement methods for MV power cables which are guided by IEEE 400 [1] and IEC 60502-2 [2] standards.

Abstract: Cable life depends mainly on the thermal stress, which relates to the current applied on the cable. Voltage changes in medium voltage (MV) cables due to transformer tap changes will also change the current flowing through the cable, which will change the cable temperature. In order to extend the cable life, this paper aims to simulate and analyse the potential thermal lifetime improvement of cables through long-term tap changes within the statutory levels. Firstly, the IEC standard (60287) method for rating and modelling cables is applied to evaluate the cable temperature under different voltages and relative currents. Different cable configurations will also be considered in simulations as temperature is dependent on the cable dimensions. Then, typical thermal lifetime analytical expressions will be used to evaluate the long-term influence of voltage changes. Lastly, the obtained thermal lifetime assessments under different transformer tap changes and different cable configurations will provide a potential understanding of cable lifetime changes through implementation of permitted regulatory voltage changes.

Abstract: High voltage termintions are essential components in high voltage cable systems. A high reliability is given by high manufacturing quality and claimed company final testing. However onsite installation represent a considerable uncertainty for successful service of the system. Commissioning testing of cable systems according to IEC60840 and IEC62067 should allow a save, undistributed service. The cable can be put into service after passing successfully a commissioning test, which is increasingly accompanied by partial discharge measurement. While a cable is in service periodically performed offline testing and diagnostic measurements rarely take place due to the fact of high efforts for switching off the cable system. Online diagnostic methods, which could be used while a cable is in service, are valuable sources for information and represent a reasonable compromise between costs and benefit. UHF PD Diagnosis has proven to be a valuable and effective method for doing so at high voltage assets (cables, GIS, transformer), because this online measurement is performed at frequencies which are not affected by environmental noise.

Abstract: Polymeric cable thermal ageing is a key end-of-life consideration for medium voltage (MV) cable, low voltage (LV) power cable, and LV instrumentation and control (I&C) cables. This is particularly true for generation plant cables. For example, in wind generation plants, low thermal design margins and component compatibility issues have been known to cause internal over-heating of conductors and accessory connectors, leading to premature cable system failures. In nuclear generation plants, cable proximity to external heat sources can often result in thermal stress being a dominant insulation ageing mechanism, a fact which is reflected in environmental qualification procedures for nuclear power plant cables. As such, numerous applied studies on electrical diagnostics for cable thermal ageing have been led by organizations such as the Electric Power Research Institute (EPRI) [1,2], the US Nuclear Regulatory Council (NRC) and Department of Energy (DOE) [3], the European Union [4].

Abstract: The development of new technologies in power generation and application, together with the demand for the reliability and capability of power supply has drawn increasing attention to dc distribution and microgrid technology. This paper introduces the renovation project for a single-circuit XLPE cable line being converted into dc operation after its second failure under 35 kV ac. This is the first time ever in China for this type of system conversion, in which the existing XLPE cable line was put into operation in a bipolar voltage-source converter (VSC) dc system of 10 kV voltage and 150 A current to maintain its 3 MW capacity. The test methods for cable performance that were checked under the designed dc scheme were put forward and conducted on sectioned cable samples. After the cable test and equipment installation, the line was put into operation under the VSC dc topology in 2011. It has now been running for four years without any interruption. Compared with other alternatives for ac operation, this proposal shows advantages in aspects of economy, reliability and engineering. Besides, the theoretical evaluation suggests that the system capacity can be further increased by four times, and the first step is underway for that goal.

Abstract: 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.

Abstract: High-temperature superconducting (HTS) power cable has significant merits of compactness and large power transmission capacity. Although the stability of the HTS cable system was verified by in-grid operation, the verification of its safety and reliability against various accidents is required for practical use of this system. A ground fault accident is one of the typical accidents of a conventional cable. If this fault occurs by breakdown of the dielectric layer, the generated arc energy is dissipated into the environment in various forms. As a result, the safety of the public may be jeopardized. Arc energy relates to arc voltage, which is dependent on the inherent physical properties of the faulted equipment. The use of coolant and the structure of the HTS cable differentiate it from a conventional cable, so it should be verified how these differences influence the arc voltage. Accordingly, ground fault tests using the HTS cable were conducted and the arc voltages were compared to that of a conventional cable. The results obtained proved that the arc voltage on the HTS cable is similar to that of a conventional cable, in spite of the differences concerning the use of coolant and the cable structure.