IC Realtime AVR-1404 User Manual

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IC Realtime AVR-1404 User Manual Manual pdf 228 page image

219Appendix G Earthing1. What is the surge?Surge is a short current or voltage change during a very short time. In the circuit, it lastsfor microsecond. In a 220V circuit, the 5KV or 10KV voltage change during a very shorttime (about microseconds) can be called a surge. The surge comes from two ways:external surge and internal surge. The external surge: The external surge mainly comes from the thunder lightning. Or itcomes from the voltage change during the on/off operation in the electric powercable. The internal surge: The research finds 88% of the surge from the low voltage comesfrom the internal of the building such as the air conditioning, elevator, electric welding,air compressor, water pump, power button, duplicating machine and other device ofinductive load.The lightning surge is far above the load level the PC or the micro devices can support. Inmost cases, the surge can result in electric device chip damage, PC error code,accelerating the part aging, data loss and etc. Even when a small 20 horsepower inductiveengine boots up or stops, the surge can reach 3000V to 50000V, which can adverselyaffect the electronic devices that use the same distribution box.To protect the device, you need to evaluate its environment, the lighting affection degreeobjectively. Because surge has close relationship with the voltage amplitude, frequency,network structure, device voltage-resistance, protection level, ground and etc. Thethunder proof work shall be a systematic project, emphasizing the all-round protection(including building, transmission cable, device, ground and etc.). There shall becomprehensive management and the measures shall be scientific, reliable, practical andeconomic. Considering the high voltage during the inductive thundering, the InternationalElectrotechnical Committee (IEC) standard on the energy absorbing step by step theoryand magnitude classification in the protection zone, you need to prepare multipleprecaution levels.You can use the lightning rod, lightning strap or the lightning net to reduce the damage tothe building, personal injury or the property, The lightning protection device can be divided into three types:Power lightning arrester: There are 220V single-phrase lightning arrester and 380Vthree-phrase lightening arrester (mainly in parallel connection, sometimes use seriesconnection ) You can parallel connect the power lightning arrester in the electric cableto reduce the short-time voltage change and release the surge current. From the BUSto the device, there are usually three levels so that system can reduce the voltageand release the current step by step to remove the thunderstorm energy andguarantee the device safety. You can select the replaceable module type, the terminalconnection type and portable socket according to your requirement.