Abstract: Harmonic characteristics of power cables used in low-voltage distribution systems of commercial buildings are investigated. Analytical discussion of cable resistance and reactance at harmonic frequencies is presented. An experimental procedure for obtaining full matrix impedance of cables at harmonic frequency is introduced. It is found that cable resistance increases with increasing harmonic order. Cable inductance, however, decreases due to the effect of flux cancellation. The analytical formulas presented yield reasonable accuracy for cable resistance for single-core cables, but provide an overestimation for multicore cables. The impact of various parameters on cable resistance and reactance, such as harmonic order, cable installation method, cable current distribution and the presence of magnetic material is also addressed, as well as the mechanisms for impedance variation. Finally, recommendations for using the approximate formulas for cables in low-voltage installations are provided.

Abstract: The partial discharge (PD) measurement is a very well known possibility to assess the quality of an insulation system. The aim of the PD-diagnostic is the detection of destruction of electrical insulation as a result of electrical stress especially of PD during operation. Therefore many methods of PD-measurement techniques have been developed in the last years. Additional to the common electrical PD-measurement with power frequency also very low frequency (VLF) and high frequency (HF) methods are applied to detect PD. In this contribution also the results of practical application of PD detection and PD localisation for cables and accessories using test voltages with 50 Hz and 0,1 Hz are represented and discussed.

Abstract: The paper reports on return voltage measurements performed on different 10 kV paper-oil insulated belted-type cables used in network systems with isolated neutral and with effective earthing of the neutral. The different cable design, e.g., the increased thickness of insulation between conductor and sheath for isolated systems, has a strong influence on the return voltage curves. Thus, a diagnostic method, which is exclusively based on single parameters such as the maximum or the initial slope of the return voltage curves, may lead to a misinterpretation. A more sophisticated evaluation method, which uses the time dependence of the complete return voltage curve is proposed in this paper.

Abstract: Three test methods for detecting the insulation defect of the XLPE power cable line, i.e., 50Hz AC voltage, 0.1Hz very low frequency voltage (VLF) and oscillating wave voltage (OWV), are compared. The experimental results show that 50Hz AC test is a preferable method to detect the defects in various types of XLPE power cable but the practicable technology needs further research. It is confirmed that 0.1Hz VLF test is quite effective in detecting moisture and water treeing in the XLPE power cable including accessories. OWV test is effective in detecting defects formed in manufacture and installation process of XLPE cable.

Abstract: Frequency-tuned resonant test systems are, meanwhile, state of the art for on-site testing and diagnostics of high-voltage extruded cables. After experience with some realised systems the technical data, especially the weightto-power ratio , and the performance have been further optimised. A specially adapted diagnostic technique has been developed for this application. Basic research on cable samples with different failures has qualified AC voltage near to the power frequency to be the optimum test voltage wave shape. Resulting from these it is logical to apply this test voltage shape also on medium-voltage cable systems. An example is introduced in this paper.

Abstract: HV cable technology is characterized by a change over from the conventional lapped paper dielectric impregnated with oil under pressure to extruded synthetic dielectrics Thermoplastic polyethylene and crosslinked polyethylene (XLPE) are increasingly used at higher and higher voltage levels because of favorable properties (low dielectric losses, simple maintenance, elimination of impregnant etc) XLPE is used extensively in most countries up to 170 kV Extensive development work and testing has lead to a breakthrough for this technology at the maximum service voltages for underground cable systems, ie 420 kV in France, Denmark and Germany and 525 kV in Japan A challenging aspect in this connection has been the development of feasible joints and terminations The technological evolution for submarine power cables has been more conservative than underground cables The obvious reason for this is that the high cost of eventual subsea maintenance work leads to a preference for well proven technology based upon long time service experience The trend has consequently been that the voltage level at which extruded dielectrics are used in submarine power cables is lagging in relation to maximum feasible voltage levels for underground cables For HVDC cables the extruded dielectric is so far not technically feasible for the highest DC voltages, however, it is expected that such cable systems will be introduced in the near future for submarine applications

Abstract: A paper describing advances in electronic PD site location devices through a system comprised of an added purpose-built analog-to-digital converter, which has been added to a previously developed, PC-based, digital PD detector.

Abstract: This paper considers cables in the voltage range of 33 kV to 550 kV. A wide choice of cable types exist to suit different tunnel situations. At voltages up to and including 220 kV, extruded XLPE cables offer a combination of adequate electrical performance, low maintenance and good fire performance. At voltages of 275 kV and above the most reliable cable system remains the fluid filled paper/PPL (polypropylene paper) cable, both in terms of the cable dielectric and the accessory dielectric. The risk of fire spread is greater with this type of cable and precautions are required to be taken. XLPE cables and in particular their joints are becoming available at 275, 400 and 500 kV, initially with small conductors. However, these are electrically less reliable and care is required to be taken in the specification of type approval tests, prequalification test, manufacturing routine tests, manufacturing sample tests and in jointer training. Prototype GIL (gas insulated line) systems are being proposed and although offering the advantage of high ratings, pose significant engineering problems with respect to electrical reliability and service life. Wherever possible the cable tunnel construction should be designed to suit the thermomechanical requirements of the cable system to achieve maximum circuit reliability. Flexible cables apply minimal loads to the tunnel wall. GIL cables can impose discrete loads at certain positions and this needs to be taken into account in the tunnel design.

Abstract: VLF testing is being considered as the safe alternative to DC Hipot testing of XLPE and mixed cables because of the known problem of induced space charges, which will cause premature failures in this type of cable. The IEEE work group 400.2 is working on a recommendation regarding the VLF test methodology. The paper compares different VLF technologies and discusses the correlation between field test data and test parameters.

Abstract: This paper presents dielectric spectroscopy measurements of medium voltage XLPE cable terminations. Different response types are classified and the influence of terminations on cable diagnostics is evaluated and verified with laboratory and field measurements.