Short tail lightning impulse behaviour of medium voltage line insulation

Breakdown characteristics of MV distribution and electric traction lines insulators stressed by standard and short tail lightning impulses

“…In particular the experimental determination of the dielectric characteristics of the insulations under study was accomplished, for both impulse waveshapes, using the Multiple Level Method [7].…”

“…In both cases the shape of the overvoltages stressing the line insulation may be very different from the Standard Lightning Impulse, in the following referred to as LI. In fact, estimations carried out by digital computer and a number of experimental results [1]- [7] have shown that the voltages above exhibit a shape with a time to half value T 2 , much shorter than the standard value, namely in the range of a few microseconds. Fig.…”

“…1 shows for instance an overvoltage induced by a lightning stroke to the ground in the vicinity of a MV overhead line, recorded in Japan in 1986 [8]. In particular it was found that an impulse voltage with a Short Tail (STLI) may represent better than LI the dielectric stress associated with the direct strikes to the shield wires of the lines [4] or with the lightning strikes to the nearby ground [2], [3], [5], [7]. In this respect a voltage wave with a front time of 1.2 µs and a time to half value of about 4 µs was chosen to represent the above overvoltages [2], as it is evident from the following considerations: -it is reasonable that the more sustained the tail, the more severe the stress on the line insulation, -it is not reasonable to consider lightning strokes to ground at distances greater than one thousand metres, because the induced overvoltages in these cases are very small compared with the basic insulation levels of medium voltage lines; -in addition the digital calculation shows that, in this case, the half-value time of induced voltage is approximately 4 µs.…”

Application of the Leader Progression Model in the Insulation Flashover Criterion for Lightning Performance Calculation

“…The measurement and simulation indicate that lightning overvoltage at the end of the insulator string is actually far from a standard wave, but has a short tail [3,4]. The discharge voltage of the insulator string under short-wave impulse voltage will be higher than that under the standard wave, and the short tail wave will make the volt-second characteristic curve upward; therefore, when the intersection method is adopted in lightning protection calculation of the transmission line, the lightning withstanding level will be underestimated and the lightning intruding overvoltage will be underestimated when it is adopted in the lightning protection calculation of substation.…”

Modeling of the behavior of medium voltage insulators against lightning overvoltages

“…In Fig. 9, R is the resistance for the short wavetail adjustment, R 1 " is the external front resistance, which controls the front-time, R 2 " is the external tail resistance, L is the inductance for short wavetails (CARRUS et al, 1999), and C 2 is derived by summing the additional load capacitance, stray capacitance, and insulator capacitance, which has a value of approximately C 2 . A general view of the test setup is shown in Fig.…”