What
is the difference between three phase and single phase
power?
What is a UPS?
UPS stands for uninterruptible power supply. A UPS is
a back-up power system used to prevent power loss or
damage to a computer or other critical piece of electrical
equipment.
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Why do I need a UPS?
There are many answers to that question.
A good UPS system can help prevent down time, by providing
clean power to critical systems when there is a power
anomaly.
A UPS can also protect equipment and help it last longer
by acting as a power conditioner, filtering out surges,
sages, spikes and outages.
A UPS increases the productivity of computer users
by keeping their computers functioning more reliably
and preventing work loss.
A Liebert UPS can provide back up power in a remote
or powerless situation with the dark start capability,
utilizing the batteries as a power source.
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What kind of UPS do I need?
The type of UPS needed depends on how critical the system
is which needs protection. There are three main types
of UPS: off-line or standby, line interactive, and on-line
(double conversion).
1. An off-line or standby UPS is used as an alternative
source of power when there has been a sudden loss of
utility power. An off-line UPS generally provides a
few minutes of back-up power to ride through the outage
or in the event of an extended outage, allow a gradual
shutdown of the connected equipment. An off-line UPS
has few power-conditioning features, and will rely on
battery power whenever utility power is unacceptable
for the critical load. An off-line UPS is best for desktop
computers, point-of-sale terminals or other applications
that need some power protection but are not mission
critical. An off-line UPS uses a voltage-sensing switch
to activate the DC rectifier and draw power from the
batteries when incoming power is not ideal. A standby
UPS does little or no power conditioning and primarily
acts as a switch to draw power from the batteries. Some
surge in output voltage occurs when it switches from
utility power to battery power. An off-line UPS has
no user replaceable batteries and lasts 3 years, on
average.
2. A line-interactive UPS is useful for large desktop
systems or a set of rack-mounted computers with up to
2200VA of power. While similar in functional layout
to the off-line UPS, line-interactive technology also
includes a buck and boost capability. This feature compensates
for power surges and sags of +/- 25% of the normal incoming
voltage without using batteries to regulate the voltage.
A greatly reduced battery duty cycle means that the
batteries in the UPS will last longer than in the off-line
style and that the connected equipment has a greater
degree of protection because the back-up power will
be more reliable. A line-interactive UPS has about 5
minutes of back-up time when fully loaded, which is
enough to ride out 90% of power anomalies and for extended
outages, can shut down connected equipment gradually
to prevent equipment damage. A line interactive UPS
uses a voltage sensing switch to draw power from the
batteries when incoming power is outside of the buck
and boost input voltage range. A minimal power loss
and a surge in the outgoing power occurs at the time
of transfer to the batteries. The PowerSure Interactive
series of line-interactive UPS have user replaceable
batteries and last 3 years, on average.
3. An on-line UPS is the third and best type of UPS.
True on-line UPS systems are only those that employ
double conversion topology. On-line delta conversion
or ferroressonant systems are not on-line UPS systems.
Those types of UPS are line-interactive. Liebert on-line
UPS systems range from 700 VA to 1,100 KVA in size.
An on-line UPS is designed for use with mission critical
systems that cannot go down without causing significant
work and or financial loss. The typical applications
for an on-line UPS are manufacturing equipment, telecommunications
systems, Internet service providers, financial networks,
data centers and other critical networks or systems.
An on-line UPS is constantly active, hence the name.
On-line UPS systems convert all incoming power to DC,
allows that DC power to pass across the battery circuit,
called the DC bus, and then converts the power back
into AC power and out to the protected equipment. The
critical load is electrically isolated from utility
power and receives continued highly regulated power.
There is no output power disturbance or gap when there
is a power loss or anomaly in the incoming power since
the batteries are always connected to the DC bus from
which the inverter draws its current. An on-line UPS
can also accept as low as 50% of the normal incoming
voltage without drawing power from the batteries. This
allows the battery systems to have a longer run time
and require less maintenance. In single phase UPS, on-line
UPS batteries are all hot swappable and will last five
years, on average.
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What is a VA?
VA is a unit of measurement for power, similar to a
watt or horsepower. VA stands for volt-amps. VA is used
to signify the total power requirements of a piece of
equipment. However, it is generally preferred to use
Watts to measure power, since VA can be relative to
the type of equipment and Watts is not. VA is the apparent
power that is being used, whereas Watts is the actual
power being used. Without getting too complicated, the
difference between Watts and VA is the power factor.
VA = Volts * Amps, Watts = Volts * Amps * Power Factor.
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What is Power Factor?
Power factor is a measurement of how the incoming power
is being used by a piece of equipment. Most computer
equipment has a power factor of 0.7. This basically
means that the equipment is using 70% of the incoming
VA. For example, a computer designed to use 100 VA at
a 0.7 PF is using 70 Watts. Liebert UPS systems are
designed to output power with a 0.7 power factor so
that the connected equipment does not waste power by
not using it. Some equipment is power factor corrected,
meaning its power factor is very close to 1.0. This
type of equipment is more efficient because it is utilizing
more of the incoming power and for all practical purposes
the VA rating is the same as the Watts. All of Liebert's
on-line UPS systems are power factor corrected to work
with any type of equipment and to be as efficient as
possible.
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What is the difference between
a surge suppressor and a UPS?
The biggest difference is that a UPS has battery backup
power, and a surge suppressor or TVSS device does not.
However a UPS is much more than a surge protector with
batteries. A surge protector is designed to protect
a sensitive electrical appliance from being destroyed
by power surges and spikes. A UPS has this capability,
but also conditions power so that the connected equipment
always receives an acceptable voltage. A surge protector
only protects the equipment from extreme voltage spikes
and surges. A UPS can also protect equipment from brown
outs, frequency variation, waveform distortion, outages,
as well as voltage spikes and surges, and can shut down
a computer safely in an extended blackout.
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What size of UPS do I need?
The best way to determine what size of UPS is needed
is to measure the amount of amps that are being used
by the equipment to be protected. Look on the back of
the equipment near the input power cord for a power
rating plate. On this plate or label will typically
be a maximum amp draw for one or more voltages. For
example: a computer may be rated at 8/4 Amps and 110/220
Volts. This computer uses either 4 amps at 220 volts
or 8 amps at 110 volts. 4 * 220 = 880 VA, and 8 * 110
= 880 VA, so this computer uses a maximum of 880 VA.
Another consideration is the potential for future expansion.
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How much back-up time do I
need?
Back-up time is entirely dependant upon the application.
If there is an alternative power source, such as a generator,
to supply back-up power, a few minutes is probably fine,
since a well maintained generator will come on in 30
seconds or less. More critical systems may need protection,
to protect against the possibility that the alternative
power source fails or isn't immediately available. If
no alternative power source is available, back up times
can be extended with additional batteries. However,
batteries are expensive, heavy, and large, so be reasonable
with expectations, and know that most power anomalies
are over in five minutes are less.
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What is the difference between
three phase and single phase power?
Single-phase power is what most computers and telecommunication
systems run on, as well as most things in your home
or office. Single phase refers to the fact that one
sine wave of voltage and current is being supplied and
used. Three-phase power is used when large amounts of
power are required for industrial systems, large electric
motors and industrial equipment or a facility wide UPS.
Three-phase refers to the fact that three offset synchronous
sine waves of current and voltage are being used to
obtain approximately 1.7 times as much power each of
the individual phases.
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Power - Frequently Asked Questions