P. Wagenaars

Influence of Ring Main Units and Substations on Online Partial-Discharge Detection and Location in Medium-Voltage Cable Networks

Online partial-discharge (PD) monitoring of medium-voltage power cables is traditionally performed on a cable between two consecutive ring main units (RMUs). PD location is achieved using a sensor at each cable end. Monitoring multiple consecutive cables, with RMUs in between, using a single monitoring system is more efficient. In addition, substations and RMUs without possibilities for sensor installation can be circumvented by installing the sensor at the next RMU. This paper studies how RMUs and substations along the cable under test affect online monitoring, including their influence on detection sensitivity, location accuracy, and charge estimate accuracy. Single-sided PD measurement, including PD location, with an RMU or substation at the far end is also considered. Models for RMUs and substations are proposed and verified by measurements. The performance of online PD monitoring is studied for a number of network configurations.

Estimation of transmission line parameters single-core XLPE cables considering semiconducting layer

A power cable model for partial discharge (PD)pulse propagation requires knowledge of all factors influencingthe transmission line parameters of the cable (characteristicimpedance, attenuation coefficient and propagation velocity). These frequency dependent quantities are related, amongst others, to the dielectric properties of the semiconducting layers. This paper discusses methods to estimate the characteristicimpedance, attenuation coefficient and propagation velocity using the cable geometryand the material properties of conductor, conductor shield, XLPE and semi-conducting layers. Measurementson cable samples show that the cable characteristics can be approximated withsufficient accuracy for PD signal propagation modeling, e.g. estimating the PD magnitude at their origins.

Detection limitation of high frequency signal travelling along underground power cable

High frequency pulse injection is part of many diagnostics techniques, e.g. cable fault location. An injected pulse along an underground power cable will reflect at an impedance impurity, for instance a cable joint. These joints can be identified based on pulse reflections only if sufficiently high-frequency components can be detected. Signals with higher frequency components can provide more accurate spatial resolution but experience stronger attenuation and dispersion. This paper discusses whether pulse reflection from a cable joint can be better distinguished if detection is focused on high frequency signal content. Two aspects, considering effects of noise level and applied equipment, are discussed in detail: averaging and highpass filtering. It is shown that in presence of noise, averaging can improve signal to noise ratio also for signals below the quantization error of digital detection equipment. High-pass filtering is realized in hardware but similar results can be achieved by software implementation. However, simulation study shows that a high-pass filter itself hardly improves reflection recognition.

Power cable joint modelin high frequency

Models in high frequency range for underground power cabling system are the basis for the analysis of many condition diagnostic techniques, for instance, partial discharge (PD) monitoring. This paper focuses on modeling of power cable joints. A cascaded transmission line model is proposed for 10kV oil-filled PILC-PILC straight power cable joint in the frequency range of 300 kHz-800 MHz. It can be applied to interpret PD signal transmission and reflection behavior in power cable connections. The model is verified by S-parameter measurement.