SIOV Metal Oxide Varistors - DEMAR

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General Technical Information Taping G = Tape (SMDs are only supplied on tape) G.S. = Tape, crimp style S, S2, S3, S4, S5 (see page 153) Special codes AUTO = High energy absorption, high resistance to thermal shock E2 = High-energy varistors AUTO…D1 = High-temperature disk varistors R5 = 5,0 Lead spacing differs from standard R7 = 7,5 Lead spacing differs from standard Fabrication code: all varistors (except CN) are marked with year/week code. Example: 9609 = 9th week of 1996 34 Siemens Matsushita Components
Selection Procedure 2 Selection procedure 2.1 Overvoltage types and sources Overvoltages are distinguished according to where they originate. 2.1.1 Internal overvoltages Internal overvoltages are those overvoltages that originate in the actual system which is to be protected, e. g. through – inductive load switching – arcing – direct coupling with higher voltage potential – mutual inductive or capacitive interference between circuits – electrostatic charge – ESD. With internal overvoltages the worst-case conditions can often be calculated or traced by a test circuit. This enables the choice of overvoltage protective devices to be optimized. Selection Procedure 2.1.2 External overvoltages External overvoltages are those overvoltages that affect the system which is to be protected from the outside, e. g. as a result of – line interference – strong electromagnetic fields – lightning – ESD. In most cases the waveform, amplitude and frequency of occurrence of these transients are not known or, if so, only very vaguely. And this, of course, makes it difficult to design the appropriate protective circuitry. There have been attempts to define the overvoltage vulnerability of typical supply systems (e. g. industrial, municipal, rural) so that the best possible protective device could be chosen for the purpose. But the scale of local differences makes such an approach subject to uncertainty. So, for reliable protection against transients, a certain degree of “overdesign” must be considered. Therefore the following figures for overvoltage in 230-V power lines can only be taken as rough guidelines: – amplitude up to 6 kV – pulse duration 0,1 µs to 1 ms Where varistors are operated directly on the line (i. e. without series resistor), normally the type series S20 should be chosen. In systems with high exposure to transients (industrial, mountain locations) block varistors are to be prefered. Requirements are stipulated in IEC1000-4. Severity levels are specified in the respective product standards ( table 1 in 3.2). Tables 2a and 2b in 3.2.4 show the selection of varistors for surge voltage loads according to IEC1000-4-5 as an example. Siemens Matsushita Components 35
Page 1 and 2: SIOV Metal Oxide Varistors
Page 3 and 4: Type Survey SMD varistors Standard
Page 5 and 6: Type Survey Disk varistors Standard
Page 7 and 8: Type Survey Block varistors B32 Pag
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SIOV Metal Oxide Varistors - DEMAR

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