Summary

Equipment Failure

Almost everyone in today’s world has been affected by electronic equipment failure. These failures encompass all aspects of electronic devices and applications. Listed below are just a few:

• Home (air conditioning, security systems, appliances, televisions, audio systems, etc.)
• Medical (diagnostics, monitors, x-ray machines, electronic filing, data transmission, etc.)
• Industrial (CNC machines, injection molding, meters, computers, printers, etc.)
• Heavy Industrial (DP transmitters, measurement & control systems, power equipment, instrumentation, etc.)
• Banking (communications lines, computers, printers, fax, modems, ATM’s, etc.)
• Manufacturing (pick and place equipment, programmable logic controllers, etc.)

Without adequate protection, all electronic based equipment is at risk. Usually the failures are not seen right away. Repeated stress from normal electrical transients weaken components and lead to shortened life. Transient voltages have proven to be the leading cause of semiconductor-based equipment failure and have cost the American industry more than 10 billion dollars in equipment damage alone. At least 75% of all reported failures have been attributed to electrical overstress.

Since there are no "wear out" phenomena inherent in solid state components (semiconductors) the life of such equipment should be indefinite. However, studies have shown that almost all failures of electronic equipment are caused by electrical overstress commonly referred to as: spikes, transients, surges, sags, or electrical noise. Sooner or later most of us observe our equipment going "off line" or actually experience catastrophic failure. The following information outlines the definitions of surges, where they come from, and what can be done.

Origins of Surge Voltages

Surge voltages occur in low voltage AC circuits and data lines because of direct or indirect lightning effects and system switching transients.

Switching

Utility main power system switching disturbances are created by capacitor bank switching, grid switching and switching on or off backup generators. Electrical utilities correct a fault by sending a power surge to clear a short in a service line, transformer, or other load grid short circuit. Multiple re-ignitions or re-strikes frequently occur in power factor corrector capacitor banks and can exceed three times normal system voltage. In addition, when power fails causing a "blackout" and then is restored, voltages exceeding several times primary power levels are typically generated. Short circuits and arcing faults or other system faults which cause current limiting fuses to clear or circuit breakers to trip, generate high voltages when the trapped inductive energy is released upon collapse of the electrical field. These lightning and switching surge threats to electronic equipment have been well defined by regulatory agencies such as ANSI/IEEE, IEC and Underwriters Laboratory (UL).

Switching transients can be associated with both normal and abnormal conditions. Minor switching transients (inductive "kick") occurs when appliances, air conditioners, compressors, etc., cycle or through the normal turn off of other electrical loads. Other periodic transients (100ms range) occur during each cycle of the commutation of motors, generators and other power converter type equipment. Multiple re-ignitions or re-strikes occur from air contractors or mercury switches that generate surges several times in amplitude larger than system voltage. Therefore even equipment commonly present in the home or business generates damaging transient overvoltages.

Lightning:

A lightning strike "cloud to ground" or "cloud to cloud" produces electromagnetic fields that can induce voltages on the conductors (wires) of AC circuits as well as data communication lines, phone lines, or transmission cable.

Lightning ground current flow results when a strike that discharges to the earth couples into common ground impedance paths, causing voltage differential across the ground grid and between ground-neutral or ground-line circuits. In short, the reference ground (supposedly zero voltage) is elevated a few milliseconds, therefore creating a large voltage difference between ground and the incoming power and/or data lines.

Direct lightning strikes, to high voltage primary circuits, inject high current into service transformers and produce voltages either by flowing through ground impedance or flowing through the surge impedance path of the primary conductors. Direct lightning strikes to secondary circuits may exceed the withstand capability of equipment and conventional surge protection devices rated for secondary circuit use.

Lightning causes utility company primary gap type arrestors to fire, limiting the primary voltage but coupling transients through the capacitance of mains, transformers, and injecting surge voltages in addition to those coupled by normal transformer action. Power company protective devices limit life threatening overvoltage; however, they create a number of damaging transients in the process, that may damage electronic equipment.

Lightning does not have to be close to create high voltages in any line (power, neutral ground, or communications). The effects of nature’s electricity induce voltages into all lines for miles around. These voltages near the lightning strike can be catastrophic, the induced voltages a mile away can cause high voltage that can create electronic system failures, and a few miles away can stress electronic equipment causing delayed (latent) failures.

Surge Suppressors

Electronic equipment may have many paths of entry for harmful surge voltages. These paths range from the low voltage AC line. Neutral or ground circuitry, to data I/O or telecommunication lines. The surge causes damage by appearing as overvoltage (voltage potential difference across an electronic circuit or device). When this voltage potential exceeds the rating of a component within the circuit, the component "shorts out" and usually, "follow on" current causes additional havoc in the circuit. These voltage potentials may occur from line to neutral, line to ground, neutral to ground, data line to data line, data line to ground, or data line to power mains. When one is considering protection for equipment, all doors or paths of entry should be examined and/or protected.

Surge suppressors limit the voltage potential by "turning on" when a preset voltage is reached and then absorbing part of the energy of the surge and eventually diverting all surge energy to ground. Once the surge has been dissipated, the suppressor "resets" and waits for the next surge. Crucial in the design of a suppressor is its ability to turn on rapidly and absorb or divert all the energy present in the surge and clamping or holding the "let through" overvoltage down to a level safe for exposed circuitry.

Most of today’s sophisticated electronic equipment in industry, office and home environments will experience shortened life ranging from the immediate catastrophic failure to latent failure (days to years) due to electrical overstress if left unprotected.

Poorly designed and "low end" surge suppressors may help equipment that is exposed to minor surge voltages, however, average and severe voltage overstress will eventually cause shortened equipment life and failure. This is due to the rise of "let through" voltage that occurs during a surge of larger amplitude. The overvoltage is caused by the inability of the suppressor to absorb or divert all of the surge energy present on the line.

There are a variety of quality, cost-effective products offered by CCI Surge Control which meet all surge suppression requirements for applications ranging from the main power entry into the building to the various zones of a building, to the connected electronic equipment, as well as surge control devices which mount onto the internal circuit board of the equipment. There are industrial CCI Surge Control products that protect equipment devices such as traffic control , measurement, control, and data transmission instrumentation.

Click Here for detailed information about Filtering and Surge Suppression Fundamentals