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| Uninterruptible Power Supply (UPS) Glossary |
Ambient Temperature: Environment temperature where a UPS is operating or kept in storage.
Unless stated otherwise, the UPS will function within its specifications in the Operating
temperature region. Storage temperature, is the allowed ambient temperature for handling and
storing the UPS, while preserving its operational characteristics.
Ampere-Hour (AH): A figure indicating battery capacity, generally defined for 5, 10 or 20 Hours
discharge time. AH figure should be divided by the discharge time to get the maximal discharge
current. The AH capacity is a function of discharge time, decreasing at short
backup times. Thus, 20H rated 10AH battery, may supply only 3.5AH for 15 minutes or 2.5AH
for 5 minutes. Battery capacity also depends on temperature, aging, number and depth of
discharge cycles, and preventive maintenance.
ASAI (Average Service Availability Index): Electric Utility Reliability Index that represents the
ratio of total customer minutes that service was available to total customer minutes demanded in a
time period. 2003 USA Average ASAI =0.9994. (source: Electric Department City of Wadsworth).
ATS (Automatic Transfer Switch): See Transfer Switch.
Audible Alarm: An audible signal enunciated upon mains outage or UPS failure or warning.
Intermittent tone signals may indicate various announcements. An alarm silence button enables
disabling the audible signal.
Audible noise: Noise emitted by the UPS generally measured by dBA units, at a distance of 1or
1.5-meter from the UPS. Most UPS systems are less than 55dBA , which is relatively
quiet. High power systems ( above 60 KVA) may present noise figure of about 65dBA, which is
the level of main road high traffic environment.
Auto Dial: A feature enabling the UPS to automatically report alarm and status via a modem
to a remote location.
Automatic Battery test: A preventive test and alarm aimed to reveal weak or damaged batteries.
The test is generally performed at user selectable-programmed intervals.
Automatic Restart: A function that enables, upon Mains Power restoration, an Automatic
Restart of a UPS, which was turned off, due to batteries discharge during Power outage.
Automatic Retransfer: An Automatic transfer from Bypass to Inverter in an On-Line system.
For Conditions: see Retransfer.
Autonomy time: Battery back-up time. The time a UPS energizes the load from Batteries.
Autonomy time is strongly influenced by the percentage of actual load Watts related to
nominal Watt rating of the UPS. Thus a 1KW UPS that supplies 5 minutes when fully rated, will
generally supply more than 15 minutes with 500W load.
Auto-start: See Automatic Restart.
Availability: The degree to which a system or component is operational and accessible when
required for use. Availability = 100 x MTBF/ (MTBF + MTTR)
Example: For MTTR of 24H and MTBF figure of 100,000 H. The availability is 99.976 %. This
means, that the UPS is operational during 8757.9H per year and is down during a time totaling 2.1
hours per year.
AVR (Automatic Voltage Regulator) : An electronic circuit that regulates output voltage in order
to keep it within allowed band limits.
Backfeed protection: Protection aimed to avoid power backfeed to the utility grid through
the Bypass from the output , in order to prevent possibility of Hazardous Voltage risks on the
distribution board, when the utility mains power is disconnected. UL Standard requires this
protection to operate even if two transfer switch components fail simultaneously.
Back-up time: See Autonomy time.
Balanced Load: Equal loading on each phase at the output of a three-phase UPS.
Battery Charger: Functional UPS module that converts the utility mains AC voltage to DC
voltage for charging batteries, in order to restore the charge that was withdrawn during mains
outage. Generally, system's Rectifier fulfills also the charging function.
Battery circuit breaker: A circuit breaker connected to the battery, enabling manual battery
isolation for maintenance purpose, and battery protection in case of DC buss short circuit.
Battery current limit: A function that limits battery-charging current. VRLA batteries in
float charging regime do not generally require current limiting, this function is therefore not
always available.
Battery end Voltage: The lowest battery voltage for system operation. Generally, the UPS
will shut down when battery voltage drops to end voltage set point. Certain systems adjust this set
point automatically according to the actual discharge current. Typical end voltage rating is
1.75V/cell , or 10.5V for a 12V battery.
Battery-Less UPS : Electromechanical Backup system using ride through energy stored in a
flywheel to backup load after power outage until local generator kicks in.
See Electro-mechanical UPS
Black Start (Cold Start): The ability to turn a UPS on from batteries, without mains.
Blade UPS : Uninterruptible power supply aimed to feed Blade Computers, mainly used in
Data Centers. It has generally a hybrid topology, working normally from conditioned mains, thus
enabling higher efficiencies compared to double conversion systems.
BSI (British Standard Institute): BSI is the National Standards body of the UK. It develops
standards and standardization to meet the needs of business and society.
Boost Charging: A charging method used to restore batteries to their full capacity after a
deep discharge or after long storage duration. Boost charging is performed, by applying relatively
high voltage (generally 2.4V/cell for VRLA battery) for a limited time.
By-Pass: Functional UPS module that connects the load of an On-Line UPS directly to mains in
case of overload or UPS failure.
CAIDI: Consumer Average Interruption Duration Index. A reliability index used by Electric
Utilities to measure in hours the average power interruption experienced by single customer.
It represents the mean time that takes the utility to restore service.
2003 USA average CAIDI was 66 minutes per interruption ( source: Electric Department city of
Wadsworth).
CBEMA Curve : See ITI Curve.
CE Marking: Manufacturers declaration that the product complies with the essential
requirements of the relevant European health, safety, and environmental directives.
Cenelec: European Committee of Electrotechnical Standardization.
Charger: See Battery Charger.
Charger Control: Control of charger's output voltage or current . Main controlled parameters:
Temperature compensation of float voltage, Transfer from boost charge regime to float voltage,
Battery current limit, Input current limit (used mainly when working from generator).
Cold Standby operation: A sleep or idle mode operation of the UPS (generally normal mode
in Off-Line systems), aimed to decrease power consumption. The UPS starts operating in
case of power failure or upon receiving an external command and will be able to support load
after the turn on interval.
Cold Start: See Black Start.
Cos Phi: The cosine of the angle between the voltage and current waveforms with the
fundamental source frequency.
Crest factor: The ratio between the Peak and the RMS values of a periodic current waveform.
The Crest Factor of a sinusoidal current waveform is 1.4142.
Current Harmonic Distortions (THDI): See THD.
Current sharing: A function or electronic circuit that causes equal current sharing between
parallel-connected UPS systems.
Unless stated otherwise, the UPS will function within its specifications in the Operating
temperature region. Storage temperature, is the allowed ambient temperature for handling and
storing the UPS, while preserving its operational characteristics.
Ampere-Hour (AH): A figure indicating battery capacity, generally defined for 5, 10 or 20 Hours
discharge time. AH figure should be divided by the discharge time to get the maximal discharge
current. The AH capacity is a function of discharge time, decreasing at short
backup times. Thus, 20H rated 10AH battery, may supply only 3.5AH for 15 minutes or 2.5AH
for 5 minutes. Battery capacity also depends on temperature, aging, number and depth of
discharge cycles, and preventive maintenance.
ASAI (Average Service Availability Index): Electric Utility Reliability Index that represents the
ratio of total customer minutes that service was available to total customer minutes demanded in a
time period. 2003 USA Average ASAI =0.9994. (source: Electric Department City of Wadsworth).
ATS (Automatic Transfer Switch): See Transfer Switch.
Audible Alarm: An audible signal enunciated upon mains outage or UPS failure or warning.
Intermittent tone signals may indicate various announcements. An alarm silence button enables
disabling the audible signal.
Audible noise: Noise emitted by the UPS generally measured by dBA units, at a distance of 1or
1.5-meter from the UPS. Most UPS systems are less than 55dBA , which is relatively
quiet. High power systems ( above 60 KVA) may present noise figure of about 65dBA, which is
the level of main road high traffic environment.
Auto Dial: A feature enabling the UPS to automatically report alarm and status via a modem
to a remote location.
Automatic Battery test: A preventive test and alarm aimed to reveal weak or damaged batteries.
The test is generally performed at user selectable-programmed intervals.
Automatic Restart: A function that enables, upon Mains Power restoration, an Automatic
Restart of a UPS, which was turned off, due to batteries discharge during Power outage.
Automatic Retransfer: An Automatic transfer from Bypass to Inverter in an On-Line system.
For Conditions: see Retransfer.
Autonomy time: Battery back-up time. The time a UPS energizes the load from Batteries.
Autonomy time is strongly influenced by the percentage of actual load Watts related to
nominal Watt rating of the UPS. Thus a 1KW UPS that supplies 5 minutes when fully rated, will
generally supply more than 15 minutes with 500W load.
Auto-start: See Automatic Restart.
Availability: The degree to which a system or component is operational and accessible when
required for use. Availability = 100 x MTBF/ (MTBF + MTTR)
Example: For MTTR of 24H and MTBF figure of 100,000 H. The availability is 99.976 %. This
means, that the UPS is operational during 8757.9H per year and is down during a time totaling 2.1
hours per year.
AVR (Automatic Voltage Regulator) : An electronic circuit that regulates output voltage in order
to keep it within allowed band limits.
Backfeed protection: Protection aimed to avoid power backfeed to the utility grid through
the Bypass from the output , in order to prevent possibility of Hazardous Voltage risks on the
distribution board, when the utility mains power is disconnected. UL Standard requires this
protection to operate even if two transfer switch components fail simultaneously.
Back-up time: See Autonomy time.
Balanced Load: Equal loading on each phase at the output of a three-phase UPS.
Battery Charger: Functional UPS module that converts the utility mains AC voltage to DC
voltage for charging batteries, in order to restore the charge that was withdrawn during mains
outage. Generally, system's Rectifier fulfills also the charging function.
Battery circuit breaker: A circuit breaker connected to the battery, enabling manual battery
isolation for maintenance purpose, and battery protection in case of DC buss short circuit.
Battery current limit: A function that limits battery-charging current. VRLA batteries in
float charging regime do not generally require current limiting, this function is therefore not
always available.
Battery end Voltage: The lowest battery voltage for system operation. Generally, the UPS
will shut down when battery voltage drops to end voltage set point. Certain systems adjust this set
point automatically according to the actual discharge current. Typical end voltage rating is
1.75V/cell , or 10.5V for a 12V battery.
Battery-Less UPS : Electromechanical Backup system using ride through energy stored in a
flywheel to backup load after power outage until local generator kicks in.
See Electro-mechanical UPS
Black Start (Cold Start): The ability to turn a UPS on from batteries, without mains.
Blade UPS : Uninterruptible power supply aimed to feed Blade Computers, mainly used in
Data Centers. It has generally a hybrid topology, working normally from conditioned mains, thus
enabling higher efficiencies compared to double conversion systems.
BSI (British Standard Institute): BSI is the National Standards body of the UK. It develops
standards and standardization to meet the needs of business and society.
Boost Charging: A charging method used to restore batteries to their full capacity after a
deep discharge or after long storage duration. Boost charging is performed, by applying relatively
high voltage (generally 2.4V/cell for VRLA battery) for a limited time.
By-Pass: Functional UPS module that connects the load of an On-Line UPS directly to mains in
case of overload or UPS failure.
CAIDI: Consumer Average Interruption Duration Index. A reliability index used by Electric
Utilities to measure in hours the average power interruption experienced by single customer.
It represents the mean time that takes the utility to restore service.
2003 USA average CAIDI was 66 minutes per interruption ( source: Electric Department city of
Wadsworth).
CBEMA Curve : See ITI Curve.
CE Marking: Manufacturers declaration that the product complies with the essential
requirements of the relevant European health, safety, and environmental directives.
Cenelec: European Committee of Electrotechnical Standardization.
Charger: See Battery Charger.
Charger Control: Control of charger's output voltage or current . Main controlled parameters:
Temperature compensation of float voltage, Transfer from boost charge regime to float voltage,
Battery current limit, Input current limit (used mainly when working from generator).
Cold Standby operation: A sleep or idle mode operation of the UPS (generally normal mode
in Off-Line systems), aimed to decrease power consumption. The UPS starts operating in
case of power failure or upon receiving an external command and will be able to support load
after the turn on interval.
Cold Start: See Black Start.
Cos Phi: The cosine of the angle between the voltage and current waveforms with the
fundamental source frequency.
Crest factor: The ratio between the Peak and the RMS values of a periodic current waveform.
The Crest Factor of a sinusoidal current waveform is 1.4142.
Current Harmonic Distortions (THDI): See THD.
Current sharing: A function or electronic circuit that causes equal current sharing between
parallel-connected UPS systems.
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An extensive and comprehensive UPS Glossary, which describes UPS and related Power
Quality and Protection terms.The entries provide detailed account about the main meaning
and use of the term , its application, along with clarifying examples.
Quality and Protection terms.The entries provide detailed account about the main meaning
and use of the term , its application, along with clarifying examples.