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	What You Can’t See May Hurt You Power protection safeguards computers, telephone switches, process control systems and other sensitive electronic equipment against damaging power disturbances, which occur with surprising frequency and at a large – but often unaccounted – cost to business. For example, a 1992 study by the International Electrical and Electronic Engineers (IEEE) organization determined that a computer system at a typical site in the United States experiences an average of 72 power disturbances each year! Although some power disturbances are generated externally on utility transmission lines, the majority are caused by the operation of electrical loads inside a facility. The culprits might include large motor loads switching on or off, electronic lighting ballasts, variable frequency drives, substandard facility wiring. or even computer power supplies. Most are not highly noticeable power outages or lightning strikes, but rather more undetectable events such as over-or under-voltage conditions, high-frequency electronic noise, or harmonics, which is particularly prevalent today. High-voltage surges and spikes can cause electrical arcing in electronic circuits. Low-voltage conditions require equipment to compensate by consuming more current, which stresses circuits, creates excessive heat, and over time, degrades hardware and eventually causes premature failure of electronic components or actual damage to the equipment’s power supply and other components. Harmonics can cause severe damage to a facility’s electrical infrastructure, including overheating of transformers, conductors, capacitors, and motors. Harmonic currents also cause voltage distortion which can lead to equipment malfunctions and premature failure. In addition to significant computer hardware damage, these events can also cause serious information processing problems, including data corruption, processing errors, and downtime resulting from system "crashes." As a result, the overall cost of power disturbances can be extremely high, not only in dollar amounts, but in terms of lost employee productivity, missed business opportunities, and damaged customer relationships as well. Because it is not possible to "see" power disturbances without sophisticated monitoring systems, they are often overlooked as the cause of data and equipment problems. However, with proper power-protection equipment in place, it is possible for businesses to successfully mitigate the risks – and the resulting costs – of unreliable power.

	Types of Power Disturbances:

	Transients	Transients or "spikes" are very short-duration over-voltage and over-current power surges. The most dramatic transients are caused by lightning strikes, but a majority are caused by large power loads switching on and off. The latter category represents roughly 80 percent of the transients found in buildings, and are referred to as "electronic rust."

	Sags	Sags or "brownouts," among the most commonly recorded power disturbances, occur when there is a momentary voltage drop of 20 percent or more. For example, instead of 110 volts, 90 volts or less may be delivered to a computer. Sags cause electronic equipment to compensate for less voltage by using more current, creating excess heat, stressing electronic components, and increasing the risk of burning out components.

	Surges & Swells	Normal utility power is transformed to 100 volts for most electronic equipment. Power surges are momentary conditions where the voltage can jump to over 100 percent of the peak voltage, or more than 220 volts. Swells are over-voltage conditions that occur over longer durations, with excess voltage of 10 percent above normal for a period of time. Both surges and swells can cause electrical arcing, or "short circuits."

	Electronic Line Noise	Line noise is a high-frequency electrical distortion of voltage waveforms, leading to "static" in electrical power lines. The presence of electronic noise is a major source of communication errors between computers and telecommunications equipment. As computer chips process at higher clock speeds, data becomes more susceptible to corruption due to line noise.

	Harmonics	Harmonics are lower frequency electrical currents that are generated by electronic equipment (non-linear loads). These currents travel in the electrical system (line and neutral conductors) and cause voltage distortion (under voltage) and energy losses.

	Power Interruptions	Power interruptions are the loss of one or more phases of power. Loss of all power phases is a power outage, or "blackout."

	Causes of Power Disturbances:

	Bad Weather	Studies by the IEEE have shown that bad weather is the leading cause of power disturbances on utility transmission lines, with wind, ice storms, and lightning responsible for about half of all significant power disturbances. Wind gusts can cause uninsulated high-voltage power lines to slap together, creating voltage surges. Strong winds and ice storms can bring tree limbs down on power lines. And lightning, which strikes power lines with surprising frequency, can cause voltage surges and spikes and occasionally destroy transformers, leading to widespread blackouts.

	Utility Grid Switching	Utility grid switching is another major – and increasingly common – source of power disturbances. Electric utilities produce electricity from a number of power-generation facilities and allocate the power to specific grids of users. The needs of the users change constantly, while the power-generation facilities produce a relatively constant output. Because the equipment used to produce power runs most efficiently at a constant speed, the utilities adjust the allocation of power, rather than making constant adjustments to the power facility’s generation equipment. As utilities switch the supply of power from one grid to another, power disturbances occur, including transients or spikes, and under- and over-voltage conditions. Power fluctuations from utility grid switching are likely to become a larger problem with increased utility deregulation and less utility company cooperation.

	Utility Equipment Failure	While all electric utilities work to maintain their equipment, and periodically replace old equipment before it fails, transformers, power lines, and switches still malfunction and fail periodically. When this happens, power disturbances occur. And, although rare, animals chewing on utility equipment insulation can occasionally cause equipment failure and lead to power disturbances.

	Accidents	Vehicle and construction equipment accidents are a minor but still significant source of power disturbances. Car and truck accidents occasionally result in damage to power poles, power lines, and power distribution equipment, causing blackouts or voltage fluctuations as other equipment on the grid attempt to compensate.

	Arc Welders & Electronic Motors	Electric arc welders and electric motors are responsible for most transient high-frequency noise. When an arc welder is welding, or an electric motor is operating, distortions to the voltage waveform are created and reflected back to the power source. High-frequency electronic noise can exceed a building transformer’s capacity to condition power, and the power disturbance can affect sensitive electronic equipment. These problems occur especially in buildings where construction or renovation is taking place, often on other floors or parts of the structure.

	Electronic Loads	Many of today’s electronic loads, also called non-linear loads, actually cause power disturbances known as harmonics. Loads such as electronic lighting ballasts, online UPS systems, variable frequency drives, DC power supplies, and computer switch-mode power supplies all convert commercial AC power to DC power. These loads draw power in pulses, switching on and off several times per second. The product of this switching is electrical currents at different frequencies from the standard 60 Hz frequency delivered by the utility company.

		The currents are reflected back through the building’s power lines to the power source, which is usually a large transformer in an electrical room or basement. Manyof these current harmonics are trapped in the transformers, which cause them to be warm to the touch. This heat is evidence of excessive transformer losses (and higher building cooling requirements). The cumulative effect of many electronic devices with switch-mode power supplies can also overwhelm the transformer’s ability to maintain clean power, leading to under-voltage situations.

	Remedies to Power Disturbances:

	TVSS or SPDs	Transient Voltage Surge Suppressors or Surge Protection Devices can protect electronic loads against voltage transients and spikes. Some of these devices also contain filters to protect against electronic line noise.

	Harmonic Cancellation Transformers	These transformers are designed for today’s electronic or non-linear loads. Special transformer windings prevent harmonic currents from becoming trapped inside the transformer. This produces much higher transformer operating efficiencies (98-98.5% vs. 85-89%), and much cleaner voltage waveforms, which the electronic loads need in order to operate properly.

	Power Conditioners	These systems are designed to regulate the voltage, so they provide excellent protection against voltage sags, and swells. Many of today’s power conditioners also offer protection against electronic line noise.

	UPS Systems	Uninterruptible Power Supplies offer the best all-around protection against the majority of power disturbances. UPS systems provide noise isolation, regulate the output voltage, and protect against utility blackouts, but have limited built-in protection against transients and spikes.

	Micro Turbines	Micro turbines, which are typically powered by a natural gas source, provide outage protection for non-emergency loads for an unlimited period of time. While not intended to replace a UPS system, the micro turbine can be used for standby power requirements, peak shaving, and cogeneration requirements.

	For More Information

	To learn more about power protection requirements and solutions, contact PowerLink Corporation.

	Phone	408-399-3355

	Email	kcastleberry@powerlinkcorp.com