Philips varistors safety Philips Passive Components Philips

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application note Philips Passive Components
Philips varistors safety
Philips Passive Components
Philips varistors safety
Philips varistors inherently robust and, when used within their rating, exhibit very failure rates. when subjected surges well beyond their peak current ratings, varistors fail short-circuit some instances, open circuit condition lead solder melts. Because their large peak pulse capability, however, these types failure quite rare properly selected devices. During short-circuit failure, varistor dissipates large amount power which lead component igniting. guard against this, only products meeting stringent antiflammability requirements should used. this respect, Philips varistors recognized meet UL1449 standard. Their epoxy coating material classified UL94V0. Philips varistors, moreover, meet 695-2-2 antiflammability recommendations being able withstand maximum seconds duration flame.
Fusing varistor
When varistor fails short-circuit, large amount energy dissipated component, causing mechanical rupture package. minimize this potential hazard, fuse circuit, either series with varistor itself general circuit.
Fuse located series with varistor this case, fuse resistance fuse blows) resistance arcing series with varistor resistance that clamping voltage varistor-fuse combination will inevitably higher than that varistor alone. Nevertheless high-power circuits, line fuses cannot relied upon protect varistor since they generally intended blow higher current than varistor fault current. prevent destruction, varistor should preferably protected with fuse connected series. this potential hazard ignition material expulsion case fuse should blow, circuit continue further minimized protecting varistor with fuse operate without protection advisable include some means monitoring condition fuse. physical shielding. Fuse located distribution line This most usual setup. However, circuit essentially inductive, blown fuse will cause shutdown line creating transient neighbouring circuitry. It's possible determine most suitable fuse from maximum withstanding current varistor taken highest current varistor conduct without destruction. With knowledge this, minimum that fuse must able handle order provide protection varistor calculated. Examples suitable fuse currents given Table typical Philips varistor types.
Varistor failure
Failure definition life According CECC IEC, failed device defined that shows change characteristic point. Although such device still appear function normally, altered characteristic lead greater power being dissipated device could ultimately lead catastrophic failure. Table summarizes possible failure modes varistor.
Table Varistor failure modes
Operating condition Surges beyond peak current rating Surges beyond energy rating Steady-state voltages well beyond voltage rating high/average source impedance source impedance (fuse high operating temperature Failure short circuit short circuit short circuit mechanical rupture package, expulsion package material open circuit failure melting lead solder joint reduction lifetime (according Arrhenius model, log(mean lifetime) 1/(absolute temperature) increased leakage current power dissipation thermal runaway short-circuit failure
Philips Passive Components
Table Fuse currents typical Philips varistors Varistor series Maximum Fuse withstanding current current 1200 2500 4500
Clearing limits Since transient pulses rectangular increase rapidly from zero crest value thereafter decrease zero approximately exponentially, dissipated energy varistor proportional duration transient. this pulse train given equation:
0.722 .(t2
Fuse selection
Criteria selection determination important fuse selection. addition level protection rated voltage, fuse selection will based important parameters: worst-case transient current possible through varistor during life, clearing limits necessary remain below minimum current that would cause rupture varistor package. Worst-case transient current typical line impedances, worst-case transient current determined from knowledge short-circuit current line. IEEE generally appropriate basis estimating level short-circuit current (see Appendix). These summarized below. Category IEEE categories Wall outlet, lone branch circuits, telecommunications, electronics, etc: Short-circuit current Category IEEE category Major feeders, short branch circuits, fixed installations, etc: Short-circuit current Category IEEE category Systems located out-of-doors service entrances, primary supplies, overhead lines, cable systems, etc: Radially-leaded varistor discs appropriate these applications
where respectively rise time time amplitude pulse peak current pulse. single pulse lifetime varistor redrawn pulse- duration curve. figure gives example such curve series varistor disc size) voltage values between
(A2s)
CCA969
10-1
10-2
impulse duration (µs)
specified life rating possible failure short circuit package rupture
Clearing limits fuse used protect varistor general applications, short-circuit varistor failures occur values between times times that derived from maximum withstanding current. Package rupture appears level times maximum specification.
Philips Passive Components
Appendix extracts from IEEE requirements
Philips Passive Components
Philips Passive Components
Philips Passive Components
Philips Components worldwide company
Australia: Philips Components Ltd, NORTH RYDE, Tel. (02) 9805 4455, Fax. (02) 9805 4466. Austria: Philips Industrie GmbH, WIEN, Tel. (01) Fax. (01) Belarus: Philips Office Belarus, MINSK, Tel. (5172) 924/733, Fax. (5172) 773. Benelux: Philips Nederland B.V., EINDHOVEN, NL., Tel. (+31 2783 749, Fax. (+31 2788 399. Brazil: Philips Components, PAULO, Tel. (011) 2333, Fax. (011) 1849. Canada: Philips Electronics Ltd., SCARBOROUGH, Tel. (0416) 5161, Fax. (0416) 6248. China: Philips Company, SHANGHAI, Tel. (021) 6485 0600, Fax. (021) 6485 5615. Denmark: Philips Components A/S, COPENHAGEN Tel. (32) 333, Fax. (31) 949. Finland: Philips Components, ESPOO, Tel. (0)-615 800, Fax. (0)-615 80510. France: Philips Composants, SURESNES, Tel. (01) 4099 6161, Fax. (01) 4099 6493. Germany: Philips Components GmbH, HAMBURG, Tel. (040) 2489-0, Fax. (040) 2489 1400. Greece: Philips Hellas S.A., TAVROS, Tel. (01) 4894 339/(01) 4894 239, Fax. (01) 4814 240. Hong Kong: Philips Hong Kong, KOWLOON, Tel. 2784 3000, Fax. 2784 3003. India: Philips India Ltd., MUMBAI, Tel. (022) 4930 311, Fax. (022) 4930 966/4950 304. Indonesia: P.T. Philips Development Corp., JAKARTA, Tel. (021) 0040, Fax. (021) 0080. Ireland: Philips Electronics (Ireland) Ltd., DUBLIN, Tel. (01) 203, Fax. (01) Israel: Rapac Electronics Ltd., AVIV, Tel. (03) 6450 444, Fax. (03) 6491 007. Italy: Philips Components S.r.l., MILANO, Tel. (02) 6752 2531, Fax. (02) 6752 2557. Japan: Philips Japan Ltd., TOKYO, Tel. 3740 5135, Fax. 3740 5035. Korea (Republic of): Philips Electronics (Korea) Ltd., SEOUL, Tel. (02) -1472, Fax. (02) 1480. Malaysia: Philips Malaysia Berhad Components Division, PULAU PINANG, Tel. (03) 5213, Fax. (03) 4880. Mexico: Philips Components, PASO, U.S.A., Tel. (915) 4020, Fax. (915) 4332. Zealand: Philips Zealand Ltd., AUCKLAND, Tel. (09) 4000, Fax. (09) 7811. Norway: Norsk Philips, OSLO, Tel. (22) 8000, Fax. (22) 8341. Pakistan: Philips Electrical Industries Pakistan Ltd., KARACHI, Tel. (021) 4641-49, Fax. (021) 035/587 4546.
Printed Netherlands 9398 50011 Date release: 11/97
Philippines: Philips Semiconductors Philippines Inc., METRO MANILA, Tel. (02) 6345, Fax. (02) 3474. Poland: Philips Poland z.o.o., WARSZAWA, Tel. (022) 2594, Fax. (022) 2327. Portugal: Philips Portuguesa S.A., Philips Components: LINDA-A-VELHA, Tel. (01) 3160/416 3333, Fax. (01) 3174/416 3366. Russia: Philips Russia, MOSCOW, Tel. (095) 6918, Fax. (095) 6919. Singapore: Philips Singapore Ltd., SINGAPORE, Tel. 2000, Fax. 1758. South Africa: S.A. Philips Ltd., JOHANNESBURG, Tel. (011) 5911, Fax. (011) 5494. Spain: Philips Components, BARCELONA, Tel. (93) Fax. (93) Sweden: Philips Components STOCKHOLM, Tel. (+46) 2000, Fax. (+46) 2745. Switzerland: Philips Components Tel. (01) Fax. (01) Taiwan: Philips Taiwan Ltd., TAIPEI, Tel. (02) 2134 2900, Fax. (02) 2134 2929. Thailand: Philips Electronics (Thailand) Ltd., BANGKOK, Tel. (02) 4090, Fax. (02) 0793. Turkey: Philips Ticaret A.S., Tel. (0212) 2770, Fax. (0212) 6707. United Kingdom: Philips Components Ltd., DORKING, Tel. (01306) 000, Fax. (01306) 345. United States: Display Wire Wound Components, ARBOR, Tel. (313) 9400, Fax. (313) 2776. Magnetic Products, SAUGERTIES, Tel. (914) 2811, Fax. (914) 0487. Passive Components, JUPITER, Tel. (561) 3300, Fax. (561) 3600. literature: (800) 3762. Yugoslavia (Federal Republic of): Philips Components, BELGRADE, Tel. 344/373, Fax. 777.
other countries apply Philips Components, Marketing Communications, BAE-1, P.O. 218, 5600 EINDHOVEN, Netherlands, Fax. +31-40-2724 547. COB13 Philips Electronics N.V. 1997
rights reserved. Reproduction whole part prohibited without prior written consent copyright owner. information presented this document does form part quotation contract, believed accurate reliable changed without notice. liability will accepted publisher consequence use. Publication thereof does convey imply license under patent- other industrial intellectual property rights.

Philips varistors safety Philips Passive Components Philips

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