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Electrical Power Basics
David Anders,The Computer Guy, a freelance systems engineer in Seattle, WA.
Resolves computer problems, assists with production issues, designs and installs networks.
http://www.apcc.com/english/power/index.cfm
Power Event Definitions, Causes and Effects
Sags: Also known as brownouts, sags are short term decreases in voltage levels. This is the most common power problem, accounting for 87% of all power disturbances according to a study by Bell Labs.
CAUSE - Sags are usually caused by the start-up power demands of many electrical devices (including motors, compressors, elevators, shop tools, etc.) Electric companies use sags to cope with extraordinary power demands. In a procedure known as "rolling brownouts," the utility will systematically lower voltage levels in certain areas for hours or days at a time. Hot Summer days, when air conditioning requirements are at their peak, will often prompt rolling brownouts.
EFFECT - A sag can "starve" a computer of the power it needs to function, and cause frozen keyboards and unexpected system crashes which both result in lost or corrupted data. Sags also reduce the efficiency and life span of electrical equipment, particularly motors.
 
Blackout: Total loss of utility power.
CAUSE - Blackouts are caused by excessive demand on the power grid, lightning storms, ice on power lines, car accidents, backhoes, earthquakes and other catastrophies.
EFFECT - Current work in RAM or cache is lost. The hard drive File Allocation Table (FAT) may also be lost, which results in total loss of data stored on drive.
 
Spike: Also referred to as an impulse, a spike is an instantaneous, dramatic increase in voltage. Akin to the force of a tidal wave, a spike can enter electronic equipment through AC, network, serial or phone lines and damage or completely destroy components.
CAUSE - Spikes are typically caused by a nearby lightning strike. Spikes can also occur when utility power comes back on line after having been knocked out in a storm or as the result of a car accident.
EFFECT - Catastrophic damage to hardware occurs. Data will be lost.
 
Surge: A short term increase in voltage, typically lasting at least 1/120 of a second.
CAUSE - Surges result from presence of high-powered electrical motors, such as air conditioners, and household appliances in the vicinity. When this equipment is switched off, the extra voltage is dissipated through the power line.
EFFECT - Computers and similar sensitive electronic devices are designed to receive power within a certain voltage range. Anything outside of expected peak and RMS (considered the "average" voltage) levels will stress delicate components and cause premature failure.
 
Noise: More technically referred to as Electro-Magnetic Interference (EMI) and Radio Frequency Interference (RFI), electrical noise disrupts the smooth sine wave one expects from utility power.
CAUSE - Electrical noise is caused by many factors and phenomena, including lightning, load switching, generators, radio transmitters and industrial equipment. It may be intermittent or chronic.
EFFECT - Noise introduces glitches and errors into executable programs and data files.
 
The Problem With Power
   There are two unfortunate realities of the electronics age; the utility simply cannot provide the clean, consistent power demanded by sensitive electronics, and the customer is ultimately responsible for the health and safe operation of his equipment.
   A study by IBM has showed that a typical computer is subject to more than 120 power problems per month. The effects of power problems range from the subtle&emdash;keyboard lockups, hardware degradation&emdash;to the dramatic&emdash;complete data loss or burnt motherboards. According to a survey by the Yankee Group, almost half of the corporations researched put their downtime costs at upwards of $1,000 per hour, with nine percent estimating costs up to or more than $50,000 per hour.
   Clearly, businesses are becoming more and more reliant on a utility power supply that is pushed beyond its capacity. Despite advances in the capabilities of modern personal computers, a momentary power outage is still all it takes to lose your data. More dangerous is the loss of previously written files, or even an entire hard disk, which can occur should a power problem strike while your computer is saving a file. Network fileservers constantly writing to disk are particularly susceptible.
   Unfortunately the situation won't be getting better anytime soon. It takes approximately a decade to get a new power plant on-line, and concerns about nuclear power and fossil fuels have stifled the construction of new generating facilities. In the United States, for instance, spending on utilities has dropped from 2.3% of the Gross National Product in the 1960's to less than 1% today.
   It's been said that there are two types of computer users: those who have lost data because of a power problem, and those who are going to. Over the past few years, we've helped create a new class... those who have recognized the need for protection and taken steps to ensure that they're prepared for the inevitable.
Are you at Risk? A Quick quiz to determine your susceptibility to power problems ...
Power problems are the largest cause of data loss
Power Failure/Surge: 45.3%
Storm Damage: 9.4%
Fire or Explosion: 8.2%
Hardware/Software Error: 8.2%
Flood & Water Damage: 6.7%
Earthquake: 5.5%
Network Outage: 4.5%
Human Error/Sabotage: 3.2%
HVAC Failure: 2.3%
Other 6.7%
 
The anatomy of a power disturbance
   Surges, spikes, blackouts and brownouts...what really happens to your computer when it experiences an out-of-bounds power anomaly?
   We'll use a nearby lightning strike as an example, although it is just one of countless problems that can strike your system.
   Lightning strikes a nearby transformer. If the surge is powerful enough, it travels instantaneously through wiring, network, serial and phone lines and more, with the electrical equivalent force of a tidal wave. The surge travels into your computer via the outlet or phone lines. The first casualty is usually a modem or motherboard. Chips go next, and data is lost.
   The utility responds to overvoltages by disconnecting the grid. This creates brownouts and blackouts. If the voltage drops low enough, or blacks out, the hard disk may crash, destroying the data stored on the disk. In all cases, work-in- process stored in cache is instantly lost. In the worst case, password protection on the hard drive can be jumbled, or the file allocation table may be upset, rendering the hard disk useless.
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Power quality is an issue that all serious computer users should be concerned with. Why? The world is becoming more dependent on computers than ever before. The Internet is changing everything in ways that could not have been imagined just a few years ago. We are now using the Web to make travel reservations, buy and sell stocks, upload and download large files and to purchase many different products. Yet the reliability of PCs and the Internet comes nowhere near the telephone system. We are always expecting dial tone when we pick up the receiver to make a telephone call, and we would be quite surprised if the telephone company would have to reboot the digital switch used in the central office. We certainly would not accept if the telephone didn't work when there was a power outage. Somehow we seem to accept much less when we log on to the Web. In time the computer industry will figure out how to design reliable software, computers and data communications equipment. The good news is that it is quite inexpensive to do something about computer crashes caused by power interruptions. Most PCs can be adequately protected for less than $159.00 with a Valuline or Professional UPS from TSi Power Corporation.
The purpose of the Power Primer is to provide some basic information about the quality of utility power and how it affects the average computer user. First a list of power anomalies and their effect on computers:
 
 
* Power outage (also known as blackout or power failure)&emdash;a complete loss of power, which causes the computer to crash and shut down.
 
* Surge voltage (also known as spike, transient or impulse)&emdash;a short-duration overvoltage, which can cause computer malfunction or failure, depending on the severity of the surge.
 
* Sag (also known as brownout or undervoltage)&emdash;a longer-term abnormal deviation from the nominal voltage of 120 V (230 V in many countries outside North-America), which can cause the computer to shut down or cause overheating of its internal power supply if the sag continues for a long time.
 
* Swell (also known as overvoltage)&emdash;a longer-term overvoltage, which can cause failure of the computers internal power supply or possible shut down for some computers.
 
What is the cause of the above problems? The power provided by the local Power Company has to be generated and distributed to the user. This process and natural events like lightning cause most problems.
Using generators that are powered by hydro, fossil fuel or nuclear fission generates power. Future supply of power will be affected by the lack of available sources of hydro and concerns over pollution caused by the burning of fossil fuel&emdash;the situation will worsen because of the lack of enthusiasm for any expansion of nuclear plants. A number of US nuclear plants are being decommissioned while countries like Sweden have decided to decommission most of its nuclear plants. Thus, it is possible that there will not be enough power to satisfy future demand in the US. Many developing countries are already experiencing severe shortages of power and have been unable to arrange the financing necessary to build more power plants. A shortage of power will cause all of the above problems, as some users will be subject to momentary power outages when there is not enough power to satisfy demand.
Power is distributed over long distances using high-voltage overhead power lines&emdash;distribution voltages can be as high as one million volts. Power is distributed locally via lower voltages provided through a series of step-down transformers. Some local distribution networks are unable to provide the power required when many users demand power at the same time, which may cause local distribution transformers to fail and hence cause power outages. Many local distribution systems in the US use overhead power lines that are very sensitive to tree branches falling and thus causing power interruptions. Additionally, surge voltages will occur when power fails as the rapid interruption of power results in a surge voltage.
The deregulation trend may compound power interruptions and stability problems in the future as switching between different power grids become more frequent as sellers and buyers exchange power.
Power problems can also be caused by thunderstorms when unwanted surge voltages from lightning strikes are delivered via the power line to the computer. Additionally, lightning arrestors on utility distribution lines can cause brief power interruptions as the momentarily short the power while diverting lightning voltages to ground.
Surge voltages can result as electrical equipment turns on and off inside buildings.
 
Helpful Terminology when Selecting a UPS
All computers and telecommunications keysystems and PBXs have a voltage and current rating and requirement. Typically, such information is printed on the back planes of equipment (near serial number and product model information) and is also included in the User's Manual. Uninterruptable Power Systems are rated in Volt Amperes or "VA." It is a simple task to determine what size UPS a particular system requires&emdash;just follow the following steps (note, the information provided applies to equipment connected to a regular 120V or 230V outlet):
 
 
* Determine required VA rating for each piece of equipment to be connected to the UPS (such as computer, monitor, modem or backup diskdrive). Multiply Volts (V) and Amps (A) for each piece of equipment and obtain VA per device. Then add the total and obtain total VA rating. For example: Computer 120V x 2A = 240 VA; Monitor 120V x 1A = 120 VA; Modem 120V x 0.1A = 12 VA. Thus the total VA is 240 VA + 120 VA + 12 VA = 372 VA. Note, if only Watts are given: multiply Watts by 1.35 to obtain the VA rating.
 
* Select a UPS that is the same rating or larger than the above calculated load. For example, a UPS-400 provides 400 VA of power and would provide at least 8 minutes of backup. If more backup is required or if more equipment will be connected to the UPS in the future, a larger UPS should be selected. A UPS-600 would provide longer backup than a UPS-400, typically 15 minutes or more. TSi Power Quality Products can provide longer backup times.
 
Would you like to know more about power? Just click: Guide to Power Terms.
The following additional articles are available from TSi:
 
IEC 1312 Comments
International Market Design
Unstable Telecom AC
Power Supplies Failure
Semiconductors Failure
UPS Limitations
Isolation Transformer Benefits
Third World UPS
Standby UPS Merits
Case Studies
Press Releases
TSi Power Primer
Guide to UPS Terms
Typical Solution Chart
World Power Database
TSi Power Corp | Products | Technical Articles | Shop Online | Contacts
 
_________________________________
TrippLite UPS site - http://www.tripplite.com/
American Power site - http://www.apcc.com/
TSi Power Corp http://www.tsipower.com/

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