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Off-line System in an off-line system, the critical load is
powered from the rawmains via the bypass line during normal
operation. The load is transferred to the UPS inverter output if
the mains fails or transgresses preset voltage limits.On-line
System in an on-line system, the critical load is fed by
conditioned power from the UPS inverter output during normal
operation. If the mains power fails, the inverter continues to feed
the load using DC power from the battery, withno switching
interruption. If the battery autonomy is exceeded, or the UPS
fails, the load can be automatically switched to an alternative
mains supply using astatic switch.MTBF Mean Time Between Failures
(MTBF) is a measure of the average time a devicewill function
before failing. MTBF ratings are measured in hours and indicate the
reliability of hardware devices such as UPS equipment.MTTR Mean
Time To Repair (MTTR) measures the total time in hours from when a
device fails until when it is restored to full operation. MTTR
includes fault diagnosis time, and any time necessary to obtain
replacement parts, as well as the actual repair work time.Power
Density the unit of power density is Watts/m. The power density of
a UPS system is found by dividing its power output in Watts by the
floor area it covers,in square metres. A high power density figure
is an important feature for UPS systems.Power Factor is a ratio
defining the relationship between useable power in Wattsand total
supplied power in VA (Volt Amperes). The power factor imposed by a
load on a UPS system can be either lagging or leading. Traditional
data centre loads have been lagging, but blade servers, which
impose a leading power factor, ar
e becoming increasingly popular because of their dense and
flexible processing power. The closer the power factor is to unity,
the greater is the power efficiency of the UPS
operation.Rectifier/Charger the part of the UPS system that
converts AC input power into DC power for feeding the conditioning
and inverter components, and charging the back-up
battery.Redundancy for highly critical loads, it is essential to
make the UPS system resilient to the failure of any single module.
This can be achieved by connecting anumber of UPS modules in
parallel to a common critical load bus. Redundancy exists if the
number of modules actually connected exceeds the number of modules
needed for the load. This means that if any one module fails, the
remainder can continue to support the critical load without
interruption.RFI Radio Frequency Interference electrical noise
resulting from some parts of t
he equipment or wiring acting as a radio antenna. The noise may
be large enoughto disrupt communications or cause computing
errors.THDi stands for the Total Harmonic Distortion of the input
current waveform. Itis generally accepted that the THDi should be
kept low to avoid excessive current distortion at the point of
common coupling within a building due to the cumulative effect of
all connected equipment.Transformerless Design UPS are now
possible, due to advances in power semiconductor technology and the
introduction of the Insulated Gate Bipolar Transistor (IGBT)
device. Transformerless design allows smaller, lighter and more
efficient UPS implementation. Other advantages include a higher
input power factor, lower THDi, reduced capital and operating
costs, lower audible noise and enhanced battery life.UPS a UPS or
Uninterruptible Power Supply is best defined as a backup power
supp
ly that, in case of a power failure, allows enough time for an
orderly shutdownof a computer or other electronic equipment, or for
a generator to take over. AUPS therefore protects computers and
other electronic equipment from mains failures and power problems.
If the mains voltage falls below a minimum level or fails entirely,
the UPS battery can maintain power to the load until either the
mains is restored or an orderly shutdown sequence is performed.
Load protection from mains borne spikes, surges and noise is also
provided.VRLA Battery VRLA or Valve Regulated Acid Batteries emit
virtually no gas, require no topping up and need no special
ventilation apart from that required by local building codes.
