PD detection in extruded power cables: an approximate propagation model

Abstract

In order to improve partial discharge (PD) detection and location in extruded power cables, Ultra-Wide Bandwidth detectors (UWB) can be preferred to wide-and narrowband systems. As UWB systems aim to get the broadest frequency content in PD pulses, it is important to evaluate the frequency attenuation as a function of distance propagated of the cable under test, trying to achieve optimum signal-to-noise ratio (SNR) and large detection sensitivity. Some conventional techniques able to calculate attenuation and dispersion of PD pulses are considered and a fast approximate model is developed in this paper, trying to provide a simple tool to estimate the maximum PD detection length in polymeric cable, in relation to bandwidth measurement system and required sensitivity.

On line partial discharge diagnosis of power cables

“…As an example, the following transformation applied to each recorded pulse can provide the equivalent time, T, and frequency, F (bandwidth), which are affected by both the nature of PD and the traveling path (through attenuation ad distortion of pulses [13][14][15][16][17][18]): The sketch of Fig. 4 illustrates an example of behavior of the T-F map, with reference to two pulses, one coming far from the detection point, the other from close.…”

“…Accordingly, the propagation characteristics (attenuation and dispersion) of PD pulses in power cables can be evaluated by modeling the frequencydependent parameters of the elementary π cell depicted in Fig. 7 [16][17][18]. The longitudinal impedance, Z, is related to skin effect losses in core and sheath conductors, and the transversal admittance, Y, depending on permittivity and losses of dielectric and semicon must be known.…”

“…The longitudinal impedance, Z, is related to skin effect losses in core and sheath conductors, and the transversal admittance, Y, depending on permittivity and losses of dielectric and semicon must be known. The propagation constant γ of a PD pulse can be thus derived from [16][17][18][19] :…”

“…It can be observed, [16][17][18][19][20], that below 1 MHz the dependence of attenuation on frequency is dominated by the skin effect; attenuation, therefore, is governed prevailingly by the geometric characteristics of the cable. Above 1 MHz losses in the transversal admittance are predominant.…”

Diagnosis of EHV and HV Transformers Through an Innovative Technique: Perspectives for Asset Management

“…In particular, they affect more markedly high frequency components, causing a strong reduction in pulse equivalent bandwidth (this quantity is defined as the standard deviation of the pulse evaluated in the frequency domain [2,4]). As an example, in power cables, PD pulse equivalent bandwidth can drop from the GHz range to a few tens of MHz in about 100 meters [5,6]. As a consequence, detectors able to evaluate PD pulse frequency content (which can be quantified, e.g., through the equivalent bandwidth concept) can provide information concerning PD source location and allow to separate contributions in the PD pattern due to multiple sources.…”