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ASSESSING RISK |
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A complete assessment of
power-related risks will help a company determine the
appropriate level of protection needed and justify the cost
of power-protection equipment. To determine the level of
protection a company requires or can afford, the following
questions should be considered:.
* Does the business experience
frequent power failures?
* Is there frequent construction
going on near or inside of the company's facilities?
* Are facilities located in areas
where server weather events occur, such as earthquakes,
tornadoes, and snow/ice/hail storms?
* Is the distribution winning in the
facilities over 20 years old? |
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* Do the facilities have emergency
generators, and do they supply power to critical systems and
network equipment outlets?
(Note: Oftentimes generators are in
place, but they supply power only to emergency lighting, some
elevators, and critical
building infrastructure systems, not
to tenants or occupants of the buildings systems.)
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* Does the company have mission-critical
business networks, systems, and/or processes that must be a
operational 24/7?
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TYPES OF POWER PROTECTION: |
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After reviewing the risks posed to
an enterprise , the appropriate power protection devices can be
selected based on the scope of interruption and potentially
faced. |
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Short term Interruptions: |
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Short-term Power anomalies such as
spikes and surges lasting only a few millionths to a few
thousandths of a second can be prevented using surge protection
devices. Placed between the network or computing device and the
power outlet it is plugged into,
a surge protector can prevent these power anomalies from
reaching the server, router ,or hub. |
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Intermediate-term interruptions |
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Intermediate-term power failures,
such as blackouts, brownouts, and electrical noise lasting from
a few seconds to 30 minutes, are treatable through
uninterruptible power supplies (UPSs). UPS devices contain
batteries and an electronic inverter, which converts DC power
from batteries to AC power required by the equipment being
protected. Software used in conjunction with a UPS can detect a
loss of power and, after a predefined period of time, cause
servers to execute their shutdown procedures. The shutdown
allows files to be closed and updated in a protected fashion,
eliminating data loss and corruption. Once power is restored,
the system is signaled to start back up. In the case of
brownouts, the UPS detects this condition and can take over the
job of supplying power in the proper operating range.
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In general, there are three different types of UPS devices. With
an offline standby power supply (SPS), 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 inventor to come on line varies by unit. The battery is
charged when line power is available. Offline UPSs do not
compensate for voltages within the 103-132Vac-input window, and
therefore are not useful in dealing with minor fluctuations in
voltage. They generally only protect systems form power spikes,
and only protect against power sags and line noise when the
battery is switched on due to a blackout. They are generally not
suitable for servers, but because of their low cost they are
often used in protecting desktop workstations. |
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When normal operating line power is present, a line-interactive
UPS system conditions power using a Ferro resonant transformer.
The UPS maintains a constant output voltage even with a varying
input voltage and provides good protection against line noise.
The UPS transformer also maintains output on its secondary
briefly when a total outage occurs. As with the offline SPS, the
line-interactive UPS switches to battery operation if it
experiences a significant power surge or complete outage. It
offers adequate protection as long as power sags or outages do
not occur with a high degree of frequency in a short period of
time, in which case the battery would switch on and off without
having enough time to completely charge. This type of failure
mode would reduce available battery time during brownout or
blackout conditions.
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With a true UPS system, power is supplied continuously from an
inverter. There is no switchover time, and such systems provide
the highest level of protection during normal operation. it can
provide line conditioning and voltage regulation and protection.
The true UPS system delivers power under all conditions and
continually recharges its battery, making it always ready to
respond if a severe power problem occurs. This type of UPS is
most often used for mission critical networks and computing
equipment requiring high availability. |
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The appropriate load size of a UPS can be calculated by adding
the volt-amperes (VA) of the devices to be connected to the UPS.
(if a devices draw is specified in volts and amperes
individually instead of VAS, the VA value can be obtained by
multiplying the volts by the amperes. If the device only
identifies the number of watts required, the VA value can be
calculated by multiplying the number of watts by 1.4 ) For
safety, the UPS should have a Va of 40 to 50 percent more than
the calculated Va value of the devices connected to it. This
will generally provide a UPS with a battery capable of supplying
power long enough to allow the protected devices connected to
it. This will generally provide a UPS with a battery capable of
supplying power long enough to allow the protected devices to
properly shut down under the maximum load size. UPS devices
should be selected with enough battery time to power protected
devices through brownouts periods. In most cases, UPSs with
battery times of at least 15 to 20 minutes are selected.
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