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Power Glossary

Ampere (A or Amp)-The unit of measure for the “rate of flow ” of electricity.

Alternating current (AC)-An electric current that reverses its direction at regularly recurring intervals.

Blackout - A zero-voltage condition lasting for more than two cycles.

Brownout - A steady state of low voltage, but not zero voltage.

Direct current (DC) - An electric current in which the flow of electrons is in one direction, such as supplied by a battery.

Double conversion - a UPS design in which the primary power path consists of a rectifier and inverter. Double conversion isolates the output power from all input anomalies such as low voltage surges and frequency variations.

Downtime - The time during which a functional unit cannot be used because of a fault within the functional unit or within the environment.

Electrical line noise - Radio frequency interference (RFI), electromagnetic interference (EMI) and other voltage or frequency disturbances.

Electromagnetic interference (EMI) - Electrical interference that can cause equipment to work improperly. EMI can be separated into conducted EMI (interference conducted through cables out of the UPS) and radiated EMI (interference conducted through the air).

Hertz (Hz) - A unit of frequency equal to one cycle per second.

High voltage spike - Rapid voltage peak up to 6,000 volts.

Hot swappable - The ability to change a module without taking the critical load off the UPS.

Input voltage range - The voltage range within which a UPS operates in “normal ” mode and does not require battery power.

Inverter - UPS assembly that converts internal DC power to output AC power to run user’s equipment.  When the inverter is supporting 100%of the load at all times, as with an online UPS, there is no break from utility power to battery power.

Kilo Voltampere (kVA) - An approximation of available power in an AC system that does not take the power factor into account.

Line-interactive - An offline UPS topology in which the system interacts with the utility line in order to regulate the power to the load.

Load - The equipment connected to and protected by a UPS.

Maintenance bypass - An external wiring path to which the load can be transferred in order to upgrade or perform service on the UPS without powering down the load.

Noise - (1) A disturbance that affects a signal; it can distort the information carried by the Signal.(2) Random variations of one or more characteristics of any entity such as voltage, current or data.(3) Loosely, any disturbance tending to interfere with normal operation of a device.

Offline - Any UPS that does not fit the definition of online. Line-interactive and standby topologies are offline.

Online - (1) A UPS that provides power to the load from its inverter 100%of the time, regulating BOTH voltage and frequency, usually double conversion topology.

Plug and play - An electrical device that does not require extensive setup to operate.

Power factor (PF) - The ratio of real power to apparent power. Watts divided by VA. Most power supplies used in communication and computer equipment have a power factor of 0.9 lag (PF =0.9 lag)

Power sag - Low voltage (below nominal 230/400 volts).

Power surge - High voltage (above nominal 230/400 volts).

Total Harmonic Distortion (THD) - Describes how much the circuit voltage deviates from a perfect sine wave. A poor voltage THD is most often manifested in a “flat topped ” waveform that comes from the inability of a power source to respond to the demands of highly non-linear loads.

Uninterruptible power systems (UPS) - An electrical system designed to provide instant, Transient-free back up power during power failure or fault. Some UPS also filter and/or regulate utility power (line conditioning).

Volt (V)/voltage - Electrical pressure that pushes current through a circuit. High voltage in a computer circuit is represented by 1;low (or zero)voltage is represented by 0.

VoltAmps (VA) - Apparent power consumption. Voltage x amps = VA.

Volts direct current (Vdc)

Volts alternating current (Vac)

Watts (W) - True power consumption. Voltage x amps x power factor = W.


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