Discharge detection techniques for stator windings

A Review of Online Partial Discharge Measurement of Large Generators

“…A number of workers in this area, e.g., Wilson et al [33], Henriksen et al [41], Gear et al [34], Pemen et al [40], have approached this problem from a variety of experimental and analytical points of view. However, despite increasing the basic understanding of what happens to a PD pulse as it propagates through a stator winding there is, as yet, no definitive theory to quantitatively describe the process.…”

“…In 1985, Wilson et al [33] found that PD pulses propagated through the stator winding by two modes, i.e., fast mode and slow mode. There is a strong distinction between fast mode of high frequency (HF, 3 MHz~30 MHz), which travels to the terminals by shorter routes than propagation along the conductor path, and slow mode of low frequency (LF, <3 MHz), of which the transit time is proportional to the length of conductor between the PD site and detection terminals [33], as listed in Table 2.…”

“…There is a strong distinction between fast mode of high frequency (HF, 3 MHz~30 MHz), which travels to the terminals by shorter routes than propagation along the conductor path, and slow mode of low frequency (LF, <3 MHz), of which the transit time is proportional to the length of conductor between the PD site and detection terminals [33], as listed in Table 2. Along with Wilson, further experiments in [34,35] indicated that the two modes of PD pulse propagation in stator windings are frequency and generator dependent.…”

“…However, the nature of the fast mode is contested anyway. It is said to be due to end-winding coupling in [33], but in [36] inductive coupling between bars of adjacent slots is expected, for frequencies even up to 20 MHz. In [34], the fast mode is thought to be capacitive coupling, while in [35] the authors wondered whether it is in fact due to displacement currents.…”

“…The critical boundary frequency between fast and slow modes is in the region of 1 MHz, whereas it is seen differently by different groups, and in some cases only the slow component is observed. There is a consensus that around 100 kHz is the best frequency range for low attenuation of PD signals throughout the entire winding [33][34][35]. …”