In this post, we will discuss the difference between lightning and surge, briefly cover the lightning and surge protection standard, and finally show a couple of Pepperl+Fuchs options for surge protection devices (SPD).
What is the difference between lightning and surge? Well, lightning occurs when you get hit by a lightning flash. The energy that comes with it is about 100 kA and it happens in less than 1 millisecond. 10/350 µs is the waveform that a lightning strike creates. At 10 µs from the lightning, the energy will be at peak, which is 100 kA, and after 350 µs, the energy will be halfway down. The graph shown below titled “Direct Lightning vs. Induced Surges” is based on a graph found in a DEHN Inc. catalog called “Lightning & Surge Protection For North American Power Systems.”
In this graph, the green waveform represents a direct lightning flash
When you have a lightning strike, a big portion of that energy goes to ground. The rest will move to any other electrical circuit nearby (by nearby, I mean 1 mile around) and that is called induced surge. The surge is also a big energy wave. Its form is 8/20 µs. At 8 µs, the surge will peak, which occurs at 5 kA, and at 20 µs, the energy will be halfway down. In the graph above, you can see the waveform of a surge in red. The surge might look small, but it can still damage your equipment.
IEC 62305-4 is the standard that talks about lightning protection for electrical and electronic systems within structures. This standard divides the areas or zones where equipment is located depending on the risk to the equipment of a lightning flash or an induced surge.
These zones are called lightning protection zones (LPZ). The zones include LPZ0, LPZ1, and LPZ2. LPZ0 is an outer zone with a higher risk of receiving a lightning flash and LPZ1 and 2 are inner zones (protected against lightning flashes but not induced surge) where an induced surge can occur.
Let’s discuss the selection of SPD (surge protection devices). The first thing we need to know is what type of signal you have and want to protect. Is it an FF, PROFIBUS PA, analog signal, a 24 V digital signal or maybe a TC / RTD signal? Each one of these options will have a different type of SPD. The good thing is that we offer all of the above.
The sketch above shows the Pepperl+Fuchs products that can be used to protect loop-powered field devices, such as a pressure transmitter and its controller. We have two protection options for this type of field device. The first one is the F*-LB* , which is a field mount device. This device is an excellent option when a junction box is not available or is not near the field device.
The second option is the K-LB*, which is a DIN-rail mounted device. This device is an excellent option when the field device is not easily accessible or there is no space available. Only one of these options needs to be used in the field. Then, we have the control side that needs its own protection. The control side can be protected using our K-LB* device as well. A good ground is required for each SPD, so the excess energy can flow out of the loop.
As I said before, we have so many SPDs for different applications that unfortunately we cannot cover all of them in this post.
Failures in electrical equipment and in measuring devices are unpleasant and lead to plant downtime. In many cases, failure can be caused by an induced surge. Because of that, SPD should always be considered for all projects.