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SIOV arrester blocks for power distribution: Reliable protection with zinc oxide varistors

Posted: 20 Dec 2000     Print Version  Bookmark and Share



APPLICATIONS VARISTORS 33Components 3/99 SIOV varistors are available both as leaded components and as SMDs. Thanks to recent advances in R&D and ongoing improvement of pro- SIOV arrester blocks for power distribution Reliableprotectionwith zincoxidevaristors The SIOV. range of zinc oxide varistors from Siemens Mat- sushita Components extends from low-voltage, low-energy varistors for ESD protection to high-voltage, high-energy ar- rester types for protection of distribution lines, substations, and other power applications. Two new products offer the electricity industry top perfor- mance and reliability at com- petitive prices. The author: PETER NVHRER, Dipl.-Ing.,works in product develop- ment for protective components at Siemens Matsushi- ta Components in Deutschlandsberg, Austria. Industry standards classify arresters by voltage or current. ANSI/IEEE C62.11, for example, defines three voltage classes: 7 distribution (up to 33 kV), 7 intermediate (up to 140 kV), and 7 station class (up to 400 kV). IEC 99-4, on the other hand, speci- fies current classes of 1500, 2500, 5000, 10 000 and 20 000 A. Siemens Matsushita Components has long been developing and man- ufacturing voltage arresters for in- termediate station class applications. Classical arresters for power distrib- ution are made of silicon carbide (SiC), but these components must always be operated in series with an air gap because of their high leakage current. SiC arresters are increasing- duction technology, Siemens Mat- sushita's Ceramic Components Divi- sion in Deutschlandsberg, Austria, can now offer two new products suit- able for all power distribution appli- cations. The SIOV E32VR302 and E32VR602 varistors for arrester blocks feature optimum technical performance and maximum reliabil- ity at a highly competitive price. Voltage arresters are used to limit spikes and pulses commonly caused by lightning strikes or switching op- erations. They are designed on the principle of insulation coordination to reduce the overvoltage to a level well below the equipment break- down voltage. Typical insulating media used are air, SF6, oil, porce- lain and polymeric materials. Accelerated stress test Fig.1 As power dissipation decreases continuously over a period of 1000 h,the E32VR302 varistor remains stable under stress conditions. 0,3 0.25 0.2 0.15 0.1 0.05 0 Powerdissipation[W] 0 5 10 15 20 25 30 35 Square root (time [h]) 34 APPLICATIONS VARISTORS Components 3/99 ly being replaced by modern zinc oxide (ZnO) arresters, which do not require air gaps. Recent studies in Australia even recommend that all gapped silicon carbide arresters with more than 13 years of service be pro- gressively replaced by ZnO compo- nents. ZnO is distinguished by minimal leakage current under normal condi- tions of operation and an excellent protection level in pulse applica- tions, resulting in a low continuous power dissipation Pc and minimal residual voltage Vr. Directly connected between the power lines and ground, ZnO ar- resters must operate with utmost reliability. Siemens Matsushita Components has con- ducted countless tests and applied years of experience in interme- diate and station class arresters to the devel- opment of heavy-duty types for power distribution. Fig. 1 shows power dissipation under accelerated stress conditions, i.e. 115 0C ambient temperature and continuous operating voltage Vc over 1000 hours. SIOV arresters for power distribu- tion meet the requirements of IEC 99-4 and ANSI/IEEE for 5 kA ar- rester types. Table 1 lists the duty cycle test defined in IEC 99-4. Al- though the test sequence applies to the entire arrester block, it is also used in practice for approval of indi- vidual components. For light and normal duty in power distribution applications, two varis- tor types with a diameter of 32 mm are currently available for arrester blocks. They are rated at 3 and 6 kV rms (rated voltage), corre- sponding to continuous operating voltages of 2.45 and 4.9 kV rms re- spectively. Table 2 lists their key da- ta. Arrester blocks are also available on request for heavy-duty distribu- tion applications (E42VRxxx se- ries), for other voltage classes and with different diameters SIOV varistors put to the test Table 1 Duty cycle test results for SIOV 5 kA arresters to IEC 99-4. Initial measurement Residual voltage measurement at In,8/20 7.3.2 Conditioning Conditioning test:4 groups of 5 pulses at In,8/20,superimposed on continuous operating voltage +20% High-current pulse High-current pulse,4/10 Preheated to 60 0C 1 3 0C High current pulse,4/10 As short as possible, not longer than 100 ms Elevated rated voltage,10 s Elevated continuous operating voltage,30 min. Cool to ambient,20 0C 1 15 0C Measurement and Residual voltage measurement at In,8/20 7.3.2 examination Visual examination of test samples Check #3-99-5 (PR) on Reader Service Card e0000000.htm Comparison of SIOV varistor types Table 2 Key data of E32VR302/E32VR602 varistors. E32VR302 E32VR602 Electrical data Rated voltage Vr 3 kV rms 6 kV rms Nominal discharge current In 5 kA 5 kA Residual voltage Vres at In <9.5 kV rms <19 kV rms Continuous operating voltage Vc 2.45 kV rms 4.9 kV rms Power dissipation Pc at Vc <0.20 W <0.40 W Reference voltage Vref at 1 mApeak >2.8 kV rms >5.6 kV rms Long duration current pulse (2 ms) 20 4 150 A 20 4 150 A High current pulse (4/10 5s)* 2 4 65 kA 2 4 65 kA Operating temperature range -25 to +600C -25 to +600C Storage temperature range -25 to +800C -25 to +800C *Additional coating required Dimensions and ordering data Diameter 34 1 1 mm 34 1 1 mm Height 22 1 0.6 mm 44 1 0.6 mm Ordering code Q69X3718 Q69X3716 Minimum marking Type,lot No., Type,lot No., Vres,Pc Vres,Pc SIOV E32VR302/E32VR602 Zinc oxide varistors at a glance Applications 7 Distribution arresters (light and normal duty) 7 Protection of overhead equipment (e.g.transformers, disconnectors,circuit breakers) 7 Suitable for arrester housings of porcelain and polymer Design 7 Passivated collar 7 Flame-sprayed metalization 7 For pressure contacts Features 7 Compliance with IEC 99-4 and ANSI/IEEE C62.11 7 Long-term stability even under stress conditions 7 Stackable for higher voltage ratings 7 Only two components necessary for 12 kV rated arresters 7 Gapless arrester design 7 No follow current S U M M A RY Siemens Matsushita's Ceramic Components Division offers new SIOV zinc oxide varistors for arrester blocks.Suitable for all power distribution applications, they feature optimum technical performance and maximum reliability at a highly competitive price.

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