Surge Arresters Save the Day

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Most likely if you follow the power cord of your laptop or desktop back to the outlet you’ll find (or you should find) that it’s connected to a surge protector to keep any delicate electronics safe from sudden electrical surges.

This is circuit protection on a small scale. But large scale electrical equipment is subject to over-voltage events too, and as much as we love our personal electronics, if a major electrical system like a power line, switching station, or power plant is thrown off-line or even destroyed by over-voltage transients, the ramifications can be extreme. These systems need circuit protection too. That’s where surge arresters come in.

A surge arrester can protect larger electrical equipment from over-voltage transients caused by external events, like a lightning strike, as well as internal switching events.  A surge arrester is connected to a conductor prior to entering the equipment, and it’s also attached to ground. It functions by safely isolating the conductor while rerouting the energy from the over-voltage to the ground, generally through a discharge device like a gas discharge tube (GDT), which is increasingly the choice of engineers because GDTs have extremely low capacitance and high insulation resistance, which makes them nearly invisible under normal operations.

Because electrical distribution systems come in all shapes and sizes, surge arresters also come in a wide variety of rating levels. Many have several lines of defense built in to address different over-voltage events. Often the actual gas discharge tube is the last line of defense in the solution, which may have a diode or TVS as the first or second lines of discharge. The LN8 series of stacked surge arresters from TDK Corporation can consist of two, four, or five individual GDT tubes soldered together. In this case, the two tube solutions resort to DC spark overvoltage at 450V, meaning that at 450V the diode and TVS have been overpowered and the gas discharge tube will be activated to arc electricity. Four tube designs spark at 1200V, and five tube designs spark at 1400V. These devices are equipped to safely handle enormous overvoltages, and they’re built to do it quickly, with a response time in a matter of milliseconds.

Typical Device Design from TDK

Under Arrest

These types of surge arresters are ideal for applications in telecommunications systems, but others are more miniature and better suited to protect data lines and Ethernet ports. These are sometimes classified in terms current handling capability. For instance, the S50 SMD Surge Arrester from TDK is a miniature 2-electrode surge arrester with medium current handling capability, ideal for applications like cable modems or DSL line cards. The S80 has a high current handling capability, more suited to antenna protection. These solutions are much more compact and designed to provide overvoltage protection in areas where space is limited.

Littelfuse offers an array of circuit protection technology with overvoltage suppression devices other than GDTs. As previously mentioned, TVS diodes and diode arrays can be used as suppressors in and of themselves outside of a greater GDT stack. Littelfuse TVS diodes have p-n junctions with larger cross-sectional areas than those of normal diodes, which allows them to conduct large currents to ground without being destroyed. TVS diode arrays are designed to protect analog and digital signal lines from harmful electromagnetic discharge. Varistors are another common suppression device, designed to suppress transient voltages at a high level, like lightening, which can be found in industrial AC line applications, as well as lower level transients.

The ideal surge arrester will be invisible within your design right up until the moment you need it most. Then, once the surge is safely grounded, it will disappear until it’s needed again. You never know when an overvoltage event can occur, but with the right surge arrester you’ll have the essential circuit protection insurance against catastrophe that your design requires. 

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