Transient Voltage Surge Suppression...

Over the past (10) years we have installed and made recommendations on hundreds of applications ranging from 3φ, 480VAC incoming power to antenna protection on a wastewater treatment facility. No matter the application, proper Transient Voltage Surge Suppression comes down to the proper device being installed at the right location, and a good ground connection. Without both of these items being correct, your equipment will be susceptable to damage and money wasted on TVSS equipment that will never function.

Question: Is there a difference between lightning and surge protection???

Answer: Absolutely there is a difference...

Of course each transient is different from one another (peak value), but the general waveform follows this pattern. Please notice that I am referring to Surge Current, which is the result of transient voltages. The over voltage will breakdown equipment because of the high potential, but the surge current is the result of a high voltage rise because the surge current is what flows and causes the burn and heat damage. Typical photos of burned up equipment is a result of Surge Current, not the over voltage. There is still much debate in the IEEE regarding what exact waveform to use for direct lightning strikes, because up until 2005, the waveform above was used for lightning as well. As a result of this waveform being used as the pattern waveform for all events, manufacturers built products to meet with this standard. These products typically were MOV technologies that where packed in sand and black plastic was used to seal the system. An MOV is a metal oxide varistor or voltage dependent resistor. They are designed for circuit boards and allow the flow of current at a specific voltage. These devices are excellent for triggering a very specific voltage; however they can not withstand much surge current because of heat generated by current flow. The sand that they are packaged with is used to dissipate heat, and the black shiny plastic is used to keep the sand in place around the MOVs.

Technical Overview

The image to the right is 8 x 20 microsecond waveform and is the IEEE C62.41 standard for switching type transients that can be generated from grid switching, inductive loads, and other events categorized as transients. The waveform gets its name from the function that at 8 microseconds, the Surge Current rises to 90% of its peak value and at 20 microseconds has fallen to 50% of its peak value.

The shaded area is a representation of energy. Test data has shown that lighting follows the general form of this 10 x 350 microsecond waveform. It is also not hard to believe that a direct lightning strike has more potential than that of a switching transient. Direct lightning strikes (on land) are typically in the range of 20-40 KA (Defined by the IEEE C62.41). As a result of this waveform being a much higher energy event, some manufacturers moved to a solution for lightning protection other than MOV technology.

The arc gap is the primary technology of direct lightning strikes protection technology. Arc gaps function very similar to spark plugs in your car; there is a build-up of voltage on the center electrode, and after a rise in potential to a pre-determined voltage, there is a spark to the side electrode (Ground). Arc gaps in lightning arrestors have been designed to trigger at much lower levels than that in your car, and because they are mechanical devices and not circuit board technology, they are designed to function thousands of times without failure.

The image to right is the 10 x 350 microsecond waveform that has been accepted by the IEEE C62.41.2-2000 in 2005 as the general form for lightning events. The standard previously mentioned categorizes the surge current of this wave form as (10 times) the energy of the 8 x 20 (shown in yellow) microsecond waveform. To better explain why, energy is a function of voltage and current over time.