3B Strikesorb wp pdf - Limotrique

Electrical:Strikesorb is designed to have minimum inductance connections while at the same time maximizing thecapacitance of the varistor disk. Its design is characterized by coaxial symmetry. This results in a devicewith minimum impedance and hence minimum response time. The thickness of the electrodes also plays asignificant role in ensuring the current through the varistor is planar/parallel (uniform) and no current‘hogging’ occurs. In conventional varistors using thin wire leads and thinner electrodes, current paths are byno means parallel and current ‘hogging’ occurs leading to reduced device surge capacity, hot spots andultimately failure under surge conditions. Figure 2 illustrates this point.Conventional varistor section unevencurrentStrikesorb varistor withparallel current paths.Figure 2:Current distribution in conventional varistors and in the Strikesorb module design.As there is insufficient electrode material, current cannot evenly spread out in the varistor disk and currenthogging occurs. It can also be seen that the path lengths for individual current filaments vary considerably,which leads to the following three effects:i. The resistance of the paths towards the outer edge of the device is higher and hence less currentflows there.ii.The transit time of the current traveling through the longer paths is higher.The consequence is that the capacity of the device is reduced below the expected material capability andthat the current density is increased due to the use of less than the total volume of the varistor which resultsin higher clamping voltage and the development of preferential paths and ultimately to failure.The Strikesorb device overcomes this by making all path lengths essentially equal and allowing sufficientlyhigh conductivity material to produce parallel current flow in the varistor slice. This leads to a device thatutilizes all varistor material equally at all frequencies.