Estimating the location of partial discharges in cables

Bandwidth and sensitivity issues in PD detection in power cables

“…Also in this case, however, results were not satisfactory, since high frequency components were not sufficiently attenuated by simply modifying the structure of the dielectric (the solution proposed in [10] works well for frequencies below 1 MHz, typically those considered in lightning propagation studies, but not above, where the effects of semicon attenuations increase remarkably with frequency [5]). To overcome these problems, the structure of the cable was modified as suggested in [11] and as reported in Figure 2.…”

“…By comparing the regression lines in Figures 6 and 7 (slope of -0.77 versus slope of -0.32) it comes out that PD pulse peak is attenuated more rapidly as a function of travelled distance when UWB detectors are employed. This phenomenon is clearly related to the larger attenuation that high frequency components suffer while travelling along the cable (associated with skin effect and semiconductive layer losses) [5] and has been used to localize PD sources in cable systems [13]. However, it should be borne in mind that the peak values of the pulses picked up by the two types of detector are quite different in absolute values: at a distance of 50 m from the PD source, the pulse entering the UWB detector has a peak value of 1.5 mV; after being processed through the IEC quasi-integrator filter, the peak value becomes 80 μV.…”

“…Testing from termination is, in general, a well accepted technique from the customer point of view: both test costs and line unavailability are dramatically reduced. However, as PD pulses travel along the cable they lose frequency content as a consequence of ohmic losses (worsened by skin effect), semicon and dielectric losses [4,5]. Thus, the larger the distance from the PD site to the coupler, the smaller the detector upper cutoff frequency that enables to achieve the best possible SNR.…”

Comparison of time-domain methods for two-end PD location in power cables

“…The PD instrument is connected to the test cable at the measuring end A and end B. The instrument contains a band pass filter and a high gain, wideband amplifier which is followed by a A/D converter and a microcomputer (PC) for signal processing [7]. The PD is simulated by injecting a narrow pulse at the distance d from the measuring end [5].…”

Insulation Diagnosis of High Voltage Apparatus by Partial Discharge Investigation

“…As can be seen, reflections have lower amplitudes and frequency content due to attenuation and dispersion (it is noteworthy that the intertime between reflected pulses is used to locate PD in cables [30]). Figure 7, taken from [31], reports the estimation of the attenuation factor as a function of frequency for a PD pulse traveling along a XLPE WV cable. It shows that the high-frequency components of a PD pulse are badly attenuated already along the cable.…”