Tips on Selecting the Right AC Power Line Protection for Industrial Applications

The reliability of industrial-based power systems and communication lines can be threatened by a variety of potential electrical issues such as power surges or nearby lightning strikes as well as the large motors or other infrastructure equipment these systems are connected to. Plus, remote industrial environments or those at higher elevations only increase the probable frequency and intensity of damage from electrical surges. What’s more, the plethora of equipment connected to the power grid is continually generating noise and energy spikes from large electrical loads or from induced line voltages.

But what is the right level of protection required for a given industrial application? Designers often have to balance the need to maximize uptime and reliability against overall cost limitations. These decisions can be tough as they understand that unplanned downtime can be expensive for their demanding customers.

Various AC power input protection solutions include popular Metal Oxide Varistor (MOV) devices. The downside of these devices is that they tend to age very quickly and fail in an industrial environment. That’s why Bourns has developed new hybrid protectors that integrate a Gas Discharge Tube (GDT) in series with the MOV. The GDT effectively keeps the MOV disconnected from the AC line until a significant voltage surge occurs, so it is not aging while disconnected. This type of solution is ideal for applications in high temperature and high humidity areas. For example, Bourns® IsoMOV™ hybrid protectors are designed to efficiently manage the current density in the MOV, are rated to 125° C with nominal surge ratings of 3 kA, 5 kA, or 8 kA, and are available with Maximum Continuous Operating Voltage (MCOV) ratings up to 555 V, making them excellent solutions for 480 V industrial power lines.

For industrial signal line protection, there are a few important design considerations when specifying customized protection for the protocol used. The common choices here tend to be TVS diodes and TISP® thyristor devices. TVS diodes either clamp or limit voltages and can be unidirectional or bidirectional. Thyristors, on the other hand, are voltage-operated switches that operate when their trip voltage is exceeded and shunt incoming surge energy to ground. TVS diodes have an advantage as their clamping function does not latch up, so TVS diodes are a good choice on lines with DC power present. And, TVS diodes are available in tightly-spaced voltage ranges so protection can be tailored to a given application with precision.

Another solution presented for challenging RS-485 installations are Transient Blocking Unit (TBU®) devices. Bourns® TBU® High-Speed Protectors are FET-based devices that can react extremely quickly. A prime solution for RS-485 protocol voltages is the Bourns® Model TBU-RS Series that integrates a TVS device directly into the TBU® HSP package, thereby providing the necessary primary protection for the TBU® device while simultaneously reducing the required PCB real estate by 52 % compared to the equivalent discrete component solution.

There are plenty of available AC power and signal line protection solutions from Bourns that are designed to help industrial systems operate reliably. Learn more in a recent Bourns article in Power Systems Design magazine.

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