Online calibration of high-frequency partial discharge signals in three-phase belted power cables

Partial discharge (PD) magnitudes from classical detection techniques are expressed in terms of apparent charges. Signals from HF/VHF/UHF techniques on substation components are often hard to express in this quantity because of complex signal excitation and propagation channels. A method to calibrate PD signals obtained during online inductive detection in medium voltage belted cables is described. online inductive detection implies that the impedances of components present in substations essentially determine the detected PD signal magnitude. The use of belted cables means, that the coupling of a PD event to the conductors not only depends on the PD site within the cross-section of the cable or cable accessory, but also becomes dependent on the momentary phase angle. In addition, during signal propagation the signal magnitude may alter according to the propagation modes of a multi-conductor cable. These aspects are studied quantitatively by the use of theoretical modelling in addition to offline and online experiments. PD diagnostic equipment including pulse injection capability allows online calibration with sufficient accuracy, irrespective of the actual substation arrangement

The design of high-voltage insulators for spacecraft traveling wave tubes

As part of a study on high-voltage design concepts used in microwave tube technology, a number of different insulator designs were studied. This work demonstrated the presence of surface charge and its effect on the voltage holdoff performance and the conditioning process. Insulators may be characterized by the breakdown voltage, the conditioning speed, and the dependence on surface charge. Insulators with anode field enhancements gave the best performance. Field enhancements at the cathode side were less harmful if stepped insulator shapes were chosen. Effective conditioning required at least a limited number of breakdowns. With sufficient conditioning breakdowns all insulator geometries tested reached an averaged breakdown field exceeding 12 kV/mm.<&gt

Frequency domain transient analysis of resonant behavior for different HV overhead line and underground cable configurations

Electrical resonant behavior in a power transmis-sion system as a result of switching or other transient generating phenomena will depend on the components applied. These components are part of a transmission system based on overhead lines (OHL) with or without embedded underground cables for the Dutch TSO TenneT. Electromagnetic transient program (EMTP) theory (in time domain) based simulation tools are nowadays widely used to analyze power transmission systems, but become time-consuming for studying effect of different parameters in large scale networks. This paper applies 1) an alternative approach to solve the differential equations composed by the system impedance and admittance matrices; 2) uses Discrete Fourier Transformation (DFT) and ABCD-matrix in frequency domain to analyze the transients. The requirement to use small simulation time-steps to correctly simulate shorter sections inside the network in time domain analysis is omitted. The approach is applied to calculate the resonant transient of a large network (combining OHL with partly 6 and partly 12 phase conductors on a single tower, and Cable with 12 mutually coupled single-core cables) located at the Randstad area in the Netherlands, and to study the influence of different network configurations on the resonant grid behavior, e.g. the influence of cable joints, number of cables, with or without cables, and so on. A comparison between this approach and PSCAD/EMTDC based on a simplified cable configuration shows that both methods give same results

Model of a double circuit with parallel cables for each phase in a HV cable connection

In Extra/High-Voltage (EHV/HV) power systems, power cables are chosen instead of over-head lines (OHL) at some places. In the Randstad region in the west of the Netherlands, the cable connection consists of a double circuit where each phase is connected via two parallel cables. The cables are cross-bonded every 0.9 km. A complete model is required to efficiently analyze interaction with the remainder of the connection consisting of overhead lines. This paper presents a method to build a symbolic model of the parallel connection of multiple cables per phase in a (EHV/HV) cable system, which can be the basis of transient analysis in the frequency domain of a large transmission system containing multiple parallel conductors. The model is analyzed and compared by means of a frequency scan of the system with PSCAD/EMTDC simulation

Remaining lifetime modelling for replacement of power transformer populations

The age of the majority of power transformers applied in the western electricity network varies between 25 and 50 years. Depending on the load history and time of operation, replacement on short term is imminent. A technically sound policy concerning the replacement of these assets must be based on knowledge of (i) the life expectancy or reliability of individual components, (ii) how these failure probabilities cumulate to a replacement wave, and (iii) how to manage an expected replacement wave. The population reliability is obtained from individual transformer reliabilities using Arrhenius based modelling of paper insulation degradation. This modelling technique includes measures to cope with inherent uncertainties in available data. Population reliability figures are obtained using an adapted k-out-of-N failure model. The modelling method is applied to existing populations of power transformers in The Netherlands, to evaluate their expected replacement wave

Influence by parasitic capacitances on frequency response of a 380-150-50 kV transformer with shunt reactor

Power transformers and shunt reactors in HV systems attract increasing attention for their transient behaviour as nowadays the systems grow more and more complex. Both devices are usually modelled by inductive components at low frequencies (e.g. 50 or 60 Hz): magnetizing and leakage inductances for transformers and phase inductances for shunt reactors. However, transients (high frequency phenomena) will boost the influence of the parasitic capacitances and require corresponding extension of their models. This paper analyzes the influence of the parasitic capacitances for a transformer (500 MVA, three-phase three-winding three-limb) and a shunt reactor (100 MVA) by building their models according to the datasheet followed by a comparison with the measurement of Sweep Frequency Response Analysis both on transformer and shunt reactor individually and on their combination