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            SELENIUM: THE FACTS 
            To date, Current Technology is the only electrical transient 
            protection industry manufacturer to incorporate selenium into 
            suppression filter system products. Selenium was a fundamental 
            component in the first Current Technology Power siftor designs 
            produced more than a quarter-century ago; many of these original 
            units remain hard at work today. Below are some of the questions 
            typically asked about the use of selenium in electrical power 
            quality offerings. Visit our Ask an Engineer page to request 
            additional information. 
            Q. What is selenium?
            A. First identified in 1817, selenium (chemical element symbol "Se") 
            is a naturally occurring element valued for its excellent 
            photoconductivity and suppression properties. Selenium has been 
            extensively studied for its cancer-preventing capabilities and is 
            included in vitamins and other dietary supplements. Selenium is one 
            of the 35 most prevalent elements in the Earth's crust. A cubic mile 
            of seawater contains approximately 14 tons of selenium. 
            Q. How is selenium used as a surge suppression element in Current 
            Technology products? 
            A. Current Technology suppression filter systems utilize selenium as 
            a rectifier -- a device that changes alternating current into direct 
            current. When connected back-to-back, selenium rectifiers provide 
            excellent bi-directional surge protection through a special process 
            that allows reverse breakdown current to conduct through the device 
            at high energy levels. 
            Q. How do selenium cells improve suppression filter performance? 
            A. By combining selenium's high steady state energy capability and 
            the excellent high surge and low clamping voltage characteristics of 
            MOVs, Current Technology delivers the industry's most reliable 
            performance and extended suppression filter system life. 
            By coordinating selenium cells as the "first line of defense" inside 
            the Current Technology suppression filter system, the selenium is 
            tasked with conducting the routine transients that are generated by 
            inductive or capacitive loads and MOV transient exposure is 
            minimized. 
            Q. Does selenium improve clamping voltages? 
            A. Yes. Steady state line voltages may vary as much as ±10% in any 
            AC power system, so it is imperative that the clamping voltage of 
            all varistor devices is well above the maximum possible system 
            voltage in order to ensure that the varistors do not conduct during 
            non-transient conditions. The high steady state energy capability of 
            selenium permits the clamping voltage to remain just above the 
            maximum steady state system voltage, thereby ensuring that the 
            selenium will be the first component to conduct the transient. In 
            most cases, MOVs utilized in Current Technology's selenium-enhanced 
            suppression filter systems encounter only small levels of transient 
            current and are therefore protected from aging. 
            Q. How does selenium safeguard against power swells? 
            A. During a power system swell, line voltage may increase to 200% of 
            its nominal level. Voltage swells may have a time duration of just a 
            few cycles or may last for several seconds. (Actual withstanding 
            duration is a function of the swell voltage amplitude and power 
            circuit line impedance.) With the addition of high energy selenium 
            cells, swell voltage may be clamped to a level that greatly reduces 
            the energy dissipated in the MOVs. By coordinating the proper 
            selection of MOV and selenium cell clamping voltages, Current 
            Technology ensures that selenium cells clamp the swell voltage to a 
            level below the critical conducting voltage of the MOVs and thus 
            protects the MOVs from catastrophic failure due to thermal runaway. 
            This added protection delivers dramatically increased long-term 
            reliability. 
            Q. What effect does selenium have on repetitive transients? 
            A. In MOV-and-selenium suppression filtering technology, selenium 
            conducts the low level, long duration surges and repetitive impulses 
            that may be present within a system, thereby minimizing metal oxide 
            varistor wear and tear. Due to selenium's continuous high energy 
            capability, no degradation is realized. The life span of the 
            suppression filter system is increased and protected loads are 
            thereby assured of extended reliability. 
            Q. Has selenium been proven as a suppression element? 
            A. Current Technology has utilized selenium as a suppression 
            component since 1971; in fact, the original Current Technology Power 
            Siftors relied on selenium alone to provide transient suppression 
            and did not include MOVs! The fact that the majority of these units 
            are still providing reliable service today is irrefutable proof of 
            selenium's excellent suppression capabilities. 
            Q. Why don't other electrical transient protection manufacturers 
            take advantage of selenium's unique and proven abilities? 
            A. The answer is threefold. First, selenium rectifiers are 
            manufactured by only a handful of skilled vendors, and availability 
            is limited. In addition, the cost of selenium is not insignificant. 
            Other manufacturers to date have apparently been more concerned with 
            profitability than product performance. Finally -- and most 
            importantly -- Current Technology's exclusive selenium-and-MOV 
            technology is proprietary and protected by a U.S. Patent. 
            Learn more about our Selenium-enhanced Plus Products 
            Ask an Engineer about Selenium. 


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