Conformity Magazine - October 2007 - (Page 39)

• The incoming surge voltage is filtered and delayed by the winding primary inductance and the capacitor. Some residual low frequency surge components appear at point B, but are delayed in time due to the filtering action of the input inductance and filter capacitance; • The canceling voltage from the tapped coil is added to the point B filtered surge, with the resultant surge cancelled voltage sent to the output; • Adding the cancelling voltage to the delayed residual surge voltage prevents even the residual surge voltage from exceeding the power wave peak voltage, reducing the surge voltage let-through to zero. (See the oscillograms later in this article for performance to worst-case surges). Since the electromagnetic interference filter uses nonsacrificial filter capacitors and inductors, and no fixed clamping components, we predict that this type of device should have a long service life. Total Surge Cancellation: Oscillogram Responses at Two Surge Levels Figures 2, 3 and 4 represent a series of oscillograms showing a brief history of 120 volt AC power quality electromagnetic interference filter surge protection responses for both a reference electromagnetic interference filter (introduced in 2002) and the total surge cancellation filter described in this article. UL 1449 Second Edition uses a suppressed voltage rating (SVR), with a minimum value of 330 volts established with a 500 ampere peak current surge, for transient voltage surge suppressor performance characterization. UL 1449 Third Edition performance characterization will use a voltage protection rating (VPR—also with a 330 volt minimum) established with a 3,000 peak ampere surge. Since UL 1449-3 assumes a fixed clamping element(s), the power wave peak voltage may be as high as 132 volts rms or 187 volts peak (multiply the rms value by 1.414 to determine the peak voltage--surges must be evaluated against the power wave peak voltage). With allowances for component tolerances and the dynamic impedance of the clamping components, a 330 volt lower limit as specified in the standard makes technical sense for products using fixed clamping voltage components. To characterize the performance of a UL 1283 Listed surge suppressing electromagnetic interference filter, we used a surge let-through voltage. The surge let-through voltage is the surge voltage that exceeds the powerline peak voltage. This measurement was used for this technology since the electromagnetic interference filter technology is dynamic, and the technology does not have a fixed voltage clamping element. The actual suppression level “tracks” the incoming power wave voltage, so the protection is optimized independent of the power line voltage. Designs are available that operate from 85 vrms to 265 vrms. This is possible since there are no fixed clamping voltage components to limit the voltage range. However, the filter components must be rated for the highest design voltage. A 4,000 volt, 2,000 amp surge was applied to the baseline electromagnetic interference filter product for reference. The two horizontal dotted lines shown on each of the oscillograms represent the normal peak positive and peak negative power wave voltage extremes. Any significant surge voltage that exceeded the horizontal dotted lines (surge voltage letthrough) could harm down-stream products. At the same time, if either the peak surge voltage let-through or its duration was reduced, the protection would be improved. Likewise, if the surge voltage was contained within the horizontal dotted lines, down stream equipment would be unaffected. Electromagnetic Interference Filter Surge Protection Performance Figure 1 illustrates the performance of a reference electromagnetic interference filter. This electromagnetic interference filter had a 100 volt surge voltage let-through pulse lasting only 17 microseconds, a significant improvement in both peak voltage and duration over conventional UL 1449 Listed technologies. october 2007 conformity 39 http://www.thehowlandcompany.com http://www.thehowlandcompany.com

Table of Contents Feed for the Digital Edition of Conformity Magazine - October 2007

Contents Editor’s Note Commission Proposes Changes for 57-64 GHz Spectrum Rules FCC Continues Actions Against Jamming Device Distributors Radio Operator Fined for Failing to Make Equipment Available for Inspection Commission Fines Unsolicited Fax Advertisers Firm Offering Quality Standards Training Also Fined Breaking New Ground with Lithium-Battery Generic Requirements for Use in Telecommunications Facilities ESD Open Forum EMC UK 2007 Conference Set Staying Abreast of U.S. E-Waste Legislation EU Commission Establishes RFID Expert Group Update on China's CCC Compliance Program System Level ESD Testing: The Waveforms An Alternative Approach to Surge Suppression Testing Equipment Buyer's Guide EU Scientific Committee Releases Updated Data on EMF Risks Updated Standards List For The EU’s EMC Directive Updated Standards List For The EU’s Directives on Measuring Instruments Call for Presentations for 2008 International ESD Workshop Announced CPSC Actions In The News IEC Standards Update Product Reviews UL Standards Update New Products From Our “You Can’t Make This Stuff Up” Department Looking Back: Items from Past Issues of Conformity Upcoming Events Advertisers

Conformity Magazine - October 2007

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