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Khamlichi A.,Polytechnic University of Mozambique | Garnacho F.,High Voltage Technological Center | Alvarez F.,Polytechnic University of Mozambique
Proceedings of the 2016 IEEE International Conference on Dielectrics, ICD 2016 | Year: 2016

A transient analysis software for high voltage cables has been developed as an aid to partial discharge measurements carried out to assess the insulation condition of installed cables. Knowledge of the transient behavior of cable systems allow to know if a specific measuring PD system is sensitive enough to detect partial discharge pulses that can occur along a high voltage cable. Series impedances of a high voltage cable are analyzed considering its semiconducting layers using Bessel functions. The influence of semiconducting layers is also taken into account to determine the parallel impedance of a high voltage cable. A Gaussian pulse is considered as a PD pulse traveling along the cable and the inverse Laplace transform is used to determine the resulting pulse at the end of a cable length. The results presented in this paper show that attenuation and distortion of PD pulses traveling along any cable system depend largely on the resistivity and the permittivity relativity of semiconducting layers of the high voltage cables. © 2016 IEEE.

Alvarez F.,Polytechnic University of Mozambique | Garnacho F.,High Voltage Technological Center | Khamlichi A.,High Voltage Technological Center | Ortego J.,DIAEL S.L.
Proceedings of the 2016 IEEE International Conference on Dielectrics, ICD 2016 | Year: 2016

Partial discharges phenomenon (PD) is one of the most relevant degradation modes that affects in the gradual deterioration of the insulation elements in high voltage (HV) electrical systems, thus PD measurement is essential for their condition assessment. In the last decades on-line PD measurements have become a common technique for assessing the insulation condition of installed HV installations, although in on-line tests it is difficult to perform accurate diagnoses due to the existence of high levels of background noise and in many cases of more than one source of pulse-shaped signals. In order to overcome the difficulties mentioned, this paper proposes a method for the classification of PD signals based on a mathematical modeling. With the proposed model, representative parameters associated to the waveform of each pulse acquired are calculated so that they can be separated in different clusters. Furthermore, this mathematical model enables the reconstruction, generally with a reasonable accuracy, of the measured signals in HV installations. This approach permits to save the pulse data of a test with a low requirement of memory capacity in comparison with other approaches, that need to save all samples of each recorded pulse to visualize them and for further analysis or post-processing. © 2016 IEEE.

Khamlichi A.,High Voltage Technological Center | Donoso G.,Red Eléctrica de España | Garnacho F.,Technical University of Madrid | Denche G.,Red Eléctrica de España | And 2 more authors.
IEEE Transactions on Industry Applications | Year: 2016

Very fast transient overvoltages (VFTOs) due to switching operations can appear between the gas-insulated substation (GIS) enclosures and the cable sheaths and between these grounding parts and the substation Earth structures. These VFTOs achieve hundreds of kilovolts, provoking hazardous disruptive discharges for human safety. This paper includes a sensitivity analysis of the different parameters in order to establish criteria to be adopted in the grounding system design of the GIS structures and the cable connection to mitigate transient overvoltages. The use of bypass surge voltage limiters (SVLs) between the GIS enclosure and the cable sheath is also needed to avoid uncontrolled discharges. The selection of these SVL according to insulation coordination rules is presented in this paper, ensuring electrical safety without affecting the current mode of exploitation of the 220-kV GIS or the cable. © 1972-2012 IEEE.

Garnacho F.,High Voltage Technological Center | Khamlichi A.,High Voltage Technological Center | Valladolid A.,High Voltage Technological Center | Simon P.,High Voltage Technological Center | Valcarcel M.,High Voltage Technological Center
IEEE Transactions on Power Delivery | Year: 2014

The k-factor function, called the test voltage function, in present standards IEEE Standard 4-2013 and IEC 60060-1, was determined years ago for voltages not higher than 100 kV and with relative overshoots around 15%. This paper presents the results of k-factor tests carried out for greater voltages up to +1.32 MV (equivalent to air-gap distances d = 2.5 m) and many test conditions. These test conditions are relative overvoltages, β′ up to 35%, different damping ratios: from δ = 0 (overshoot) to δ=35% (oscillating waveform), and different electrical configurations of a nonhomogenous electric field using air gap factors K = 1 (rod plane) up to K =1,45 (rod conductor). The results show that the present k-factor function stated in both standards does not represent insulation behavior for large air-gap distances when the gap factor K is around 1. Only when the gap factor K increases to 2, are the experimental k-factor values closer to the standard k-factor function. A general formula for the k-factor, depending on the oscillation frequency, gap distance, and the electric-field nonhomogeneity, k (f, d ,K) is derived from the performed tests, taking also into account the k-factor results of the recent bibliography. © 2014 IEEE.

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