Surge Protection device & solutions

Sources / Causes of Transient over voltages

Natural : A typical natural source of transient over voltage event is lightning.

  • Direct lightning strikeLightning strikes the structure directly. Direct lightning can inject partial lightning currents of the 10/350Ás waveform into a system where a structure with a structural Lightning Protection System receives a direct strike or where lightning directly strikes an overhead service line. Measurements of actual lightning strikes have shown that the 10/350 Ás waveform is a reasonable approximation for the current waveform for the primary lightning stroke.
  • Indirect effects of lightning strikeLightning strike to, or near, the external wiring network common to most house/s. Remote or indirect lightning flashes near the structure or near a connected service to the structure of up to 1km radius away are represented by the 8/20Ás waveform. Induced surges from direct lightning flashes and switching sources are also represented by this waveform.
Man made :Man-made sources are usually caused by induction. When switching on/off of the inductive loads (such as electric motors), or by switching heavy resistive AC loads. The switching surge comes in many different forms, and has many different sources. What is consistent between all switching surge events are:

  • They are low frequency events usually under a kilohertz and related to the fundamental power frequency.
  • They are always associated with a change in the operating state of the system.
  • They are always associated with a switching event on the power system. Unlike the lightning surge, the switching surge is generally self induced by the operation of a breaker, switch or disconnect switch. Both the IEC and the IEEE have standardized on the 8/20 Ás waveform to represent induced lightning effects.
Compression between devastating energy content in Lightning and Switching Surge Transparent Over Voltage
Overvoltage curves Comparison of a discharge of 40 kA (10/350 ms) and 40 kA (8/20 ms) A Typical Current Sharing pattern in case of Direct Lightning strike to a building structure The structural damage can normally be prevented from direct lightning strike, by routing of lightning energy through properly installed Lightning rod and down conductor. Even though the remaining Lightning energy may distribute thorough all types of conductors like Electrical power line, Data lines, communication lines, signal circuits, plumbing line etc.
Transparent Over Voltage
So it is necessary to provide surge protector at service entrance lines and point-of-use, and the way these elements work together to protect equipment inside a structure.