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

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

Detection limitation of high frequency signal travelling along underground power cable

The detection of the high frequency signal propagating along underground power cables is part of many monitoring techniques, e.g. partial discharge (PD) based diagnostics. On one hand, higher frequency corresponds to better spatial resolution, which means more accurate PD location. On the other hand, signal attenuation increases with frequency. Apart from the signal itself, noise level and detection equipment also play a role in the signal detection process. This paper focuses on the detection limitation of high frequency components in PD signals travelling along an underground power cable considering effects of signal attenuation, noise level and applied equipment. The attenuation coefficient is based on measurements from 10kV three-core XLPE cables. Though the attenuation coefficients for other types of cables differ, the measured value for this particular cable provides a practical parameter value, and it can be altered to match other cable types. The detected analog signal is digitized through an analog-to-digital converter (ADC) and may be averaged before being digitally stored. In addition, an amplifier and/or filter can be applied before the analog to digital (AD) conversion. The vertical resolution and the vertical sensitivity of the ADC are crucial for signal detection. Effect of noise is considered in this paper by analyzing Gaussian noise and typical noise characteristics obtained from field measured. Sinusoidal wave and Gaussian pulse shapes are applied as input signals for the cable. Firstly, the relationship between maximum cable length and detectable frequency components for a specific set of detection equipment conditions is analyzed without averaging. This is the limitation from ADC. Secondly, the merits and limits of averaging are studied. The required averaging time for different frequencies as a function of PD signal propagation length is studied. Finally, the effect of averaging and analog filtering is demonstrated with test measurements

Water treeing: The behaviour of water trees in extruded cable insulation

Electrical Engineering, Mathematics and Computer Scienc