- 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.
- _______________________________
-
- 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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