EFFECTS on COMPUTER EQUIPMENT
Below is a brief explanation of the ways that power
disturbances affect
computer equipment.
- Blackout - Blackouts may cause loss of
current work in RAM
or cache, possible loss of the hard drive File Allocation
Table (FAT) resulting
in total loss of data stored on drive (which may or may not
be recoverable).
- Sag or Brownout - A loss of optimal voltage could cause frozen
keyboards, dim or
bright lights, shrinking display screens, and unexpected system
crashes resulting
in the loss or corruption of data.
Sags or brownouts
also reduce the efficiency
and life span of electrical equipment, particularly motors.
According to Glenn Cross
of the Willimantic office of Connecticut Light and Power,
planned brownouts by the company are usually
preceded by plenty of warning
and result in a 5%
voltage reduction on the entire system. Assuming that you were
receiving normal voltage prior to this reduction,
a voltage drop of 5% should not cause any problems.
- Spike - A spike can cause catastrophic damage to hardware
(e.g., burn out your
PC circuit boards), as well as loss of data and processing
errors.
- Surge - Surges can stress delicate components and
over time could wear out components. In addition,
surges can contribute to data errors, dim or bright
lights, and shrinking
display screens.
- Noise - Electrical noise can introduce
glitches and errors
into executable programs and data files, but it is not harmful
to the equipment
HOW to PROTECT AGAINST ELECTRICAL DISTURBANCES
Below are some devices that
can help protect against electrical disturbances. In all cases,
it is also necessary to protect your data and programs by backing them up
frequently to external backup devices.
- Blackout - a UPS (uninterruptible power
supply) continues to
provide power (battery) when there is a loss of electrical
power. While a UPS provides
power for a limited duration, that time can be extended
by combining a UPS with a generator.
- Sag or Brownout - A regulating UPS continues
to provide the required voltage even when there is a drop in voltage.
For extended usage, one
could combine a generator with a UPS. Unstable voltage can
also be protected by
use of a voltage regulator, which is now built in to most power
supplies.
- Spike - A surge suppressor/diverter is used to protect
equipment from transient over-voltages
present on AC power, data or telephone circuits.
- Surge - A surge suppressor/diverter
is used to protect equipment from transient over-voltages present
on AC power, data or telephone circuits.
- Noise - In many cases, a UPS can smooth
out noisy power sources. Another solution is the use of a
communication line surge suppressor.
MORE INFORMATION on SURGE SUPPRESSORS and UPS
Surge Suppressors -
guard against spikes and surges that come through the AC outlets
by absorbing excess electricity and diverting it to the
ground line, away
from your computer and peripherals. There are two types of surge
suppressors:
the floor model (which resembles the conventional power strip)
and the console model
(which sits under your monitor). One should be careful in
the use of surge suppressors.
It has been found that spot placement of surge suppressors can
actually increase the incidence of electrical problems. If the
equipment is not properly
grounded when a surge suppressor shunts a surge to ground,
it elevates the ground
potential. The differences in ground voltages can cause
electrical currents
to flow in the ground circuit, which can damage non-protected
devices. Therefore,
if one device on a circuit is protected by a surge suppressor,
they all should
be protected.
UPS (Uninterruptible Power Supply)
UPS's are used to protect
against decreases in voltage (either blackouts or brownouts/sags).
A UPS switches your system over to battery power when it senses certain
electrical problems.
A UPS usually provides about 5-15 minutes of battery power.
This usually provides you with enough time to save your files and
perform a controlled system shutdown.
In general, a UPS is capable of performing the following functions:
absorb relatively small power surges, smooth out noisy power sources,
continue to provide
power during power sags/brownouts, provide power for some
time during blackouts.
Additionally, some UPS or UPS/software combinations
can perform additional
functions including the monitoring and logging of the status
of the power supply.
In general, there are three different types of UPS devices.
- Standby Power Supply
(SPS) - In this type of device, power is usually derived
directly from the
power line until power fails, at which time a battery-powered
inverter turns
on to continue supplying power. The time it takes for the inverter
to come ‘on line"
varies by unit. The battery is charged when line power
is available. Generally, a standby power supply does not
compensate for voltages withing the 103-132
VAC input window and, therefore, is not useful in dealing with
minor fluctuations
in voltage.
- Hybrid UPS systems - In this type of device,
when normal operating
line power is present, the supply conditions power using a
ferroresonant transformer.
This transformer maintains a constant output voltage
even with a varying
input voltage, and provides good protection against line noise.
The transformer
also maintains output on its secondary briefly when a total
outage occurs.
- True UPS System
- In this type of device, power is supplied continuously
from an inverter.
There is no switchover time, and they provide the best
isolation from power line problems.
COPING with ELECTRICAL DISTURBANCES at
the UNIVERSITY OF CONNECTICUT
- Computer Center - The UPS system at the University
of Connecticut Computer
Center has battery backup only, and is intended to give
the Computer Center
time to come down in a scheduled manner in the event of
power fluxes, failures,
or reduction in power flow. The UPS system is not designed
to keep the Center
running for long periods after a power interruption; it is
intended for short-term
outages of 10-15 minutes. In the event of reduction or
loss of street power,
the UPS batteries would kick in to cover the loss of power.
Computer Operations
would then call Facilities Management to determine the anticipated
time frame
for power reduction or loss. If the outage or reduction is expected
to last more
than 10 minutes, Computer Operations would then begin the shutdown
procedures and
power off the computing equipment. Once the systems and attached
devices have
been turned off, Computer Operations would then trip the battery
circuits to stop
the drain on the batteries and preserve their integrity.
- Individual Departments and Offices -
The best way to determine what preventative
measures you should
take is to first assess your own situation and to balance
your critical needs
with the cost involved. In addition to computer equipment, you
may wish to assess
non-computer equipment as well. With respect to computers,
it is wise to get
in the habit of doing frequent backups of your programs and
data to an external
device to minimize the negative effects of electrical disturbances.
- How critical
is it for you to continue to work if the power were down? If
you cannot survive
even a short-term outage (less than 4 hours) resulting in
a manageable loss in
production with reasonable backup procedures in place, then
a backup generator
would be required, as well as a UPS, since it would take some
minutes for the
generator to kick on.
- How critical are the programs and data stored on your
hard drive?If
restoring your programs and data to the most recent backups made
would still impose a hardship, then you should invest in a UPS
which would provide
you with enough uninterrupted power to permit you to back up
your critical applications and data.
If more time is required, then a backup generator
would also be
necessary.
- Could you cope with the effects of nuisance interruptions
(noise, spikes, surges)
which generally do not last very long but which
could still cause damage? Depending
on your analysis, you may wish to invest in a UPS and/or surge suppressor.
This document is courtesy of Elaine David, UCC Year2000 Coordinator,
and can be found at web site:
vm.uconn.edu/~year2000/edisturb.html
and will be posted with other Deans, Directors, Department Heads
Mailings at vm.uconn.edu/~wwwucc/uccddd.html.
Go to Top
Page last updated on 08/05/97.
Mail comments to:
wwwucc@uconnvm.uconn.edu
