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(Automatic Transfer Switch): Functional UPS module, which transfers the load from the output of the Inverter to the Bypass (fed by Utility mains or to other alternate source), and vice versa. The transfer from Inverter in Online type system is generally performed automatically in case of overload or whenever the output voltage deviates from a preset window. The Automatic Transfer Switch will generally re-transfer automatically to the Inverter (see Retransfer)
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 shortbackup 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.
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 may refer to alarms. For units with constantly running fans, this level of noise may be too noisy for office environments or for AV applications. High power systems ( above 60 KVA) may present noise figure of about 65dBA, which is the level of main road high traffic environment.
A preventive test and alarm aimed to reveal weak or damaged batteries. The test is generally performed at user selectable-programmed intervals. This is usually done through software.
A function that enables, upon Mains Power restoration, an Automatic Restart of a UPS, which was turned off, due to battery discharge during Power outage or software setting
An Automatic transfer from Bypass to Inverter in an online system. For Conditions: see Retransfer.
The time a UPS energizes the load from Batteries. Autonomy time is dependent upon the load power and battery capacity. A common misconception is that higher rated UPS provide more autonomy but this is only true if the higher rated UPS has more battery capacity.
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.
A method of providing AVR by changing the turns ratio on an output transformer to raise the voltage higher.
A method of providing AVR by changing the turns ratio on an output transformer to lower the mains voltage.
Protection aimed to avoid power backfeed to the utility grid throughthe Bypass from the output , in order to prevent possibility of Hazardous Voltage risks on the distribution board, when the utility mains power is disconnected, or on mains plug pins if the plug is removed.
Equal loading on each phase at the output of a three-phase UPS.
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.
A circuit breaker connected to the battery, enabling manual battery isolation for maintenance purpose, and battery protection in case of DC buss short circuit.
A function that limits battery-charging current. VRLA batteries infloat charging regime do not generally require current limiting, this function is therefore not always available.
The lowest battery voltage for system operation. Generally, the UPSwill 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.
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.
A charging method used to restore batteries to their full capacity after adeep 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.
Functional UPS module that connects the load of an online UPS directly to mains in case of overload or UPS failure. See UPS Bypass Operation
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).
A sleep or idle mode operation of the UPS (generally normal modein Off-Line systems), aimed to decrease power consumption. The UPS starts operating incase of power failure or upon receiving an external command and will be able to support load after the turn on interval.
The ability to turn a UPS on from batteries, without mains.
The cosine of the angle between the voltage and current waveforms, also known as power 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.
(THDI): See THD.
A function or electronic circuit that causes equal current sharing between parallel-connected UPS systems.
An Electronic device connected between the Utility Power (or alternate AC source)and electric consumers, comprising of a DC Power Supply ( Rectifier), and Battery. The DC UPS is intended to provide uninterrupted conditioned DC voltage, within strict regulation limits against any Utility Power disturbances including outages.
LCD or Led display, generally located on the UPS front, providing information about the UPS status, including voltages, currents frequency etc. The display is also used in certain systems to program system settings.
Topology of ONLINE UPS (VFI class per IEC 62040-3). The AC mains voltage is converted to DC by means of an ac to DC Rectifier (or Charger), The DC voltage is then converted to conditioned AC by means of the Inverter.
Isolated relay contacts generally used for alarm or status signalization.
Also called Dual input. UPS with separate Bypass input, enabling AC input redundancy by feeding the rectifier and the by pass from different sources. UPS output will automatically synchronize with the bypass input source.
System's output voltage deviation caused by connecting or disconnecting rated load. Generally, different values refer to linear and nonlinear type loads.
An economical mode of operation, which enables certain online UPS systems to work in an Off-Line mode from the Utility, while the inverter, which is in hot standby operation, is able to accept load upon mains failure.
(Electro-Magnetic Compatibility): The ability of equipment to perform its function without causing or suffering unacceptable degradation due to Electromagnetic Interference to or from other equipment in the same environment.
(Electro Magnetic Interference): Electromagnetic disturbance, generated mainly by switching circuits and devices, that interrupt, obstruct or degrade the limits of performance of electric equipment.
(Emergency Power Off) ? A functional module in the UPS enabling manual UPS turn offat emergency situation, like fire or safety hazards, while disabling all output voltages.
Leakage or short circuit to ground (Chassis) from isolated battery, isolated inputor output power lines, including Neutral. Some standards require activation of earth fault alarm,if the earth fault current exceeds a rated value.
System for earthing of exposed conductive parts and neutral: IT system: Neutral Isolated from earth (or high impedance to earth), exposed parts earthed Individually.TN system: Exposed conductive parts connected to earthed Neutral.TT System: Exposed conductive parts and Neutral are directly earthed.
UPS efficiency is defined as AC output Watts divided by AC Input Watts. Thefull load efficiency of Standby or Line Interactive UPS is generally within 95% to 98%, and within 90% to 95% for an Online Dual conversion system. Full load Efficiency is defined asthe ratio between stated UPS output Watts (stated Volt -Ampere capacity times stated output Power Factor) divided by input Power in Watts. For AC to DC ( Output Watts to DC bus) efficiency, see Inverter Efficiency.
( Also called: Rotary , Batteryless, or Flywheel UPS).An electromechanical Uninterruptible Power Supply that generally consists of a motor-generator and additional hardware which enables to supply short time energy by utilizing kinetic energy stored in a flywheel. It is normally applied in high power installation, by supplying the ride-through energy from primary power outage until backup generator kicks in . It offers higher efficiencies due to standby mode of operation and high Reliability due to absence of batteries.
See @Battery End voltage.
A battery located outside the electronic cabinet. In certain cases, theexternal battery is connected in addition to the internal battery for Backup time expansion.
(Field Effect Transistor): A transistor in which the current between the power terminals is controlled through the gate terminal by means of an electric field, drawing very low drivepower. It is used as high frequency switching element in low power UPS Inverters.
The ability to isolate a short-circuited load branch, by tripping its circuit breaker or fuse.
A Usystem which implements output voltage stabilization, by means of a special output transformer, utilizing the constant voltage characteristic of the transformers? saturated iron core.To eliminate the current drawn from the inverter by the magnetizing transformer, a capacitor is added to form a parallel resonant LC filter, tuned to UPS frequency.The ferroresonant method provides output isolation and harmonic filtering. The shortcomings are, relatively low efficiency, increased weight and volume.
Constant voltage charging method. See also @Float voltage.
Current drawn by a charged battery in float charging regime.
DC Voltage applied to the battery by the charger (or rectifier) in constantvoltage charging regime. The float voltage value at 25 degrees Celsius is generally 2.3V/cell for Lead-Acid battery and 1.42V/cell for Nickel-Cadmium battery. To extend battery lifetime, the float voltage should be adjusted (compensated) with temperature according to battery manufacturers recommendation.
Wet electrolyte batteries. Checking and adding water through vent caps should periodically maintain these batteries. These batteries have proven reliability of extended20 to 30 years of operation. They require large floor space, and ventilation systems, which generally limit location to dedicated battery rooms.
Electromechanical Backup system using ride through energy stored in aflywheel to backup load after power outage until local generator kicks in. See @Electro-mechanical UPS.
See @VRLA battery.
Deviation of output frequency from nominal value when the UPS is not synchronized to mains power (at mains outage). The stability is generally +/- 0.5%, with RC oscillator and +/- 0.05% with crystal oscillator.
Connecting the UPS chassis to external protective ground.
A sinusoidal component of a periodic wave, having a frequency that is an integral multiple of the fundamental source frequency.
A term sometimes used for systems which utilize high frequency waveform in the internal UPS inverter. Inverter switching is performed by high ultrasonic carrier frequency ( above 16 kHz) waveform, pulse width modulated with a sinusoidal system's output frequency waveform. The carrier frequency is attenuated by Low pass filter to provide a sinusoidal 50 or 60 Hz output waveform. This technique is today standard in almost all Line Interactive and online systems.
Battery modules or redundant modular sub-assemblies, whichcan be replaced without turning the UPS off.
A standby mode of operation generally implemented in Series redundant systems. The UPS is constantly fully operational and running without load. It starts to supply current immediately upon load connection.
Uninterruptible power supply that uses a DC to AC converter between theAC input and the DC battery buss. The converter is able to add or subtract energy fromthe mains in order to stabilize output voltage and correct input power factor.
(Insulated Gate Bipolar Transistor): A transistor which combines FET input andbipolar Transistor output, forming a switching device with very low drive power, high blocking voltage, and low conduction losses. IGBT is the most popular power-switching element in UPS inverters.
See @Earthed System.
(CBEMA Curve): An AC input voltage envelope, published by ITI council, that shows input voltage limits which typically can be tolerated ( will not cause functional interruption) by most Information Technology Equipment.According to ITI curve a computer will not turn off in short (less than 20 ms) power interruptions, or in case of line voltage sags up to 70% of nominal lasting less than 0.5Second. The curve describes also the influence of high input voltage on computer operation continuity.
The distortion of the AC input current due to harmonics. The distortions are measured by means of input current THDI figure at the AC input of the UPS. Some standards limit the maximum allowed input current distortions. Most systems today limit THDI distortion to less than 10%.
The distortion of the AC input voltage due to harmonics. The distortions are measured by means of input voltage THD figure at the AC input of the UPS.
The initial current at the input of the UPS upon turn on (see Rectifierwalk-in). Also the initial current a consumer draws from the UPS upon turning on the consumer. The inrush current is generally caused either, due to charging of DC filter capacitors, or because of sub-cycle magnetizing current of a transformer, located in the turned on equipment.
A battery located inside the UPS cabinet.
Functional UPS module that inverts the DC battery voltage to 50Hz or 60Hz AC voltage.
Also called AC to DC efficiency: AC Output Watts divided byInverter Input Watts, when load is connected to Inverter output. (Inverter input wattsequals DC buss voltage multiplied by the current drawn by the Inverter). Inverter efficiency is used for calculating battery capacity. Ratings vary from 80% at low DC voltages to 95%, at high DC buss voltages. Full Load Efficiency is defined as Rated Output Watts (Rated Volt-Ampere times stated output power factor) divided by DC input Current times Nominal DC input Voltage.
Generally refers to the allowed maximum KV ( Kilo-Volts) between input and ground, output and ground and input to output in UPS systems with isolation transformer.
A transformer connected at the input of the UPS to isolate the battery from the utility grid, or at the output of a UPS to isolate the load from the utility grid.
Power factor of an Inductive type circuit, in which the currentlags behind the source voltage (negative cos phi)
A rechargeable battery common in UPS systems, it is composed oflead plates suspended in electrolyte solution of sulfuric acid and water.
Power factor of a capacitive type circuit, in which the currentleads the voltage (positive cos phi).
See @primary power.
A system, which energizes the load from the utility mains providing conditioned power by filtering and stabilizing mains voltage (VI class per IEC 62040-3). Upon mains outage the load is energized from batteries via the Inverter.
Load comprised of linear (non switching) components, such as, resistors, capacitors, inductors, motors, lamps, transformers etc.
(Mean Time between failures): The average expected time between failures, generally expressed in hours. MTBF figure is the reciprocal of the failure rate figure (λ). Example: MTBF of 100,000 hours means that a system which works continuously is expected to fail once in 11.41 years. Total MTBF figure of a site with 200 such systems is 500H (100,000/200), such site is expected to experience about 18 failures per year (365*24/500).MTBF figure refers generally to failures that let the UPS down. It is either a value calculated according to Reliability Standards, or based on actual Field experience.
(Mean Time To Repair): The time (generally expressed in Hours) from failure incident, until the system is repaired and restored to normal operation.MTTR should take in account in addition to actual field repair time, also detection time, travel time, waiting time etc.
See @VRLA battery.
A communication protocol which enables monitoring and control of distributed devices in a network from a master supervisory computer.
A redundant method based on one module more than needed to fulfill the required performance. For instance, three parallel systems, each rated 2KVA, form a 2+1 redundant system for a 4KVA consumer. Failure of a single UPS will not affect systems operational performance.
Acoustical noise measured in dBA units, generally at a distance of 1meter or 1.5 meter from the UPS. Typical noise levels (in dBA): quite room: 40; office 45-55; vacuum cleaner (3m): 70, disco: 100.
The product of nominal cell voltage multiplied by number of cells connected in series. The no load circuit voltage of a charged single battery cell is defined asthe nominal cell voltage and equals 2V for lead acid battery and 1.25V for Nickel-Cadmium battery (generally abbreviated as 1.2V). Thus, the nominal voltage of a 6 cells lead acid battery equals 12V.
Load comprised of switching components, such as diodes, rectifiers, Thyristors, Switching or Pulse modulating systems or circuits. Nonlinear loads generate current and voltage harmonics with integral multiple frequencies of fundamental source frequency.
Operational state is termed Normal, when Utility Power is available and within ratings, the battery is charged, the load is within rating and it is fed from the preferred (default) source (Mains Power if Stand-By , Inverter if online system).
(Passive Standby): A system, which normally energizes the load directlyfrom the utility mains (see VFD classification by IEC 62040-3). It contains a charger and an Off-Line Inverter. The Inverter is switched ON upon mains outage to supply the load.
(True on line ): A double conversion system, which energizes the load continuously from the inverter. The inverter is fedfrom mains via a rectifier in normal operation, or from batteries upon mains outage.
Generally, the output waveform of the inverter. It can be either Sinusoidal, or Rectangular. Some manufacturers call the rectangular waveform by such names as Semi-Sinusoidal or Quasi Sinusoidal. Rectangular waveform may cause undesirableoperation with certain loads. The manufacturer should therefore be consulted before application.
The maximum current, which the Inverter is able to supply at rated voltage.
The Harmonics at the output voltage of the UPS. These Harmonics are measured by means of output voltage THDV figure.
The deviation of output voltage from its nominal rating, due to changes in other parameters, like load, battery voltage, ambient temperature, mains voltage, within their allowed and rated limits.
The maximum load current allowed for a limited time while still keeping rated conditioned voltage. Typical, Inverter overload is 125% of full load for 10 minutes 150% for 30 seconds.
(Power Factor Correction): Correction of input Power factor by means of decreasing the harmonic currents at the input of the UPS. PFC is generally implemented by means of special filters, multiple pulse rectifiers or electronic functional modules.
(Pulse width modulation): Modulation technique in which the duration of pulses isvaried in accordance with some characteristic of the modulating signal. The technique is implemented in UPS systems in PFC circuits, Rectifiers and Inverters.
Operation of two or more systems with outputs connected to a common Load Buss for Redundancy or power enhancement purpose. To enable parallel operation the UPS systems should have equal output voltages, operate synchronously (same frequency and same phase), and have load-sharing capabilities.
A combination of more than two systems operating in parallel, that includes at least one Redundant (extra) unit which is not required to provide the total expected load. A failure of a single UPS does not affect system performance, thus increasingdramatically load power Availability.
Generally relates to the angle between the output phase voltages in a three phase UPS. Ideally, the phase angle should be 120 degrees. Practically a deviation exists, due to system and load unbalance..
(W/VA): Actual Power divided by Apparent (or Total power). In new UPS systems with power factor ( PF) correction, UPS input power factor is greater than 0.95.UPS Output power factor is currently 0.7 in most cases. New regulations require to increase servers input power factor above 0.9. UPS Watts and VA should exceed respective load ratings.More on this see UPS Sizing.
(Power Outage): Any degradation of AC power below the minimum ratedvalue, generally lasting more than 10 mS, which may cause the loss of service to a customeror facility.
Power disappearance for a short period (generally seconds to minutes).
The ten most frequent disturbances (IEC 62040-3): 1.Power outage (>10ms), 2.Voltage fluctuations (<16ms), 3.Voltage transients (4.16ms),4.under-voltage (continuous), 5.over-voltage (continuous), 6.Lightning effects (sporadic <1ms), 7.Voltage surges(<4ms), 8.Frequency fluctuations (sporadic), 9.Voltage bursts( periodic), 10.Voltage harmonics(continuous).
Energy source feeding the UPS. Generally Utility power. See @primary power or @Standby Generator.
External AC supply from the Utility grid (or other AC power source). Generally: Single-phase 230V 50Hz, or 120V 60Hz; Dual voltage 120/240V 60Hz; Three Phase 230/400V 50Hz, 120/208V 60Hz.
(Remote Emergency Power off) ? EPO function activated by remote signal (generally by means of external dry contacts). The EPO should be associated with disconnection of all energy sources to the UPS (including batteries).
(Root Mean Square): RMS value, also called Effective value, equals the square Root ofthe Mean value of the Squared amplitudes of all harmonics in a waveform divided by square root of 2 (1.414). Current RMS value, equals the equivalent direct current that would produce the same power dissipation in a given resistor. The RMS values of current or voltage are generally measured with a ? True RMS ? meter.
A Communication Standard for Serial signal transmission between a computer and peripheral devices. The maximum distance is about 50feet (16m). Generally, the connection is made between UPS to the computer by means of 9 or25 pin D-Type connector (often using only three wires) directly, or through modem and telephone line.
A 4 wire Communication Standard for Serial signal transmission between a computers and peripheral devices. The maximum distance is 4000 feet (1200 m). One driver can be connected to up-to 10 receivers. .
A 2-wire Communication Standard for Serial signal, multi point transmission. The maximum distance is 4000 feet 1200m). The standard specifiesup to 32 drivers and 32 receivers on a single buss.
Battery which can be recharged (as opposed to one time battery).See @VRLA battery.
Functional UPS module that converts the utility mains input voltage to DC voltage.In Off-Line systems, the rectifier is used for battery charging. In most online systems the Main Rectifier is used to charge the batteries and feed the load through the Inverter
Rectifier protection, that limits the maximum current which can be drawn from the rectifier. Rectifiers' current limit setting takes in account the DC currentdrawn by Inverter at full rated load, and in addition the current required to recharge thebatteries.
A gradual increase of output voltage, aimed to limit Inrush currents. Generally, the walk in time may take up to 5 seconds.
A method based on using one or more extra backup modules, which enable normal system performance even in case of system failures. For example, redundancy is achieved by feeding a consumer of 1KVA by means of two 1KVA rated UPS systems connected in parallel, hence single unit failure does not affect load performance.
The probability that equipment will perform satisfactory during a specific time.
The ability to turn a system on or off, monitor its behavior or to change it?s setting from remote location.
Manual or automatic Retransfer of Load from Bypass to Inverter in an online system. Generally enabled only when no fault condition exists, Inverter output voltage is in phase with Bypass voltage and the load is within its nominal rating.
Electromechanical Backup system using ride through energy stored in a flywheel to backup load after power outage until local generator kicks in. See Electromechanical UPS
A rectifying device which allows unidirectional current flow when triggering pulse is applied to the gate. SCRs are used as switching element in UPS Static Transfer Switch and frequently as the rectifying element in high power UPS Rectifiers.
(Simple Network Management protocol): A transmission Internet Protocol (TCP/IP)used to manage and control IP gateways and the networks to which they are attached
(Solid State Relay): An electronic module substituting generally a relay with a single Normally Open AC contact.
Ability to increase the output power of the UPS in user's premises, by additional modules or UPS systems, in parallel with existing units.
A configuration of two systems, with only one (The main UPS)supplying load current via its transfer switch. The second is a backup unit operating normallyin Hot Standby mode. Backup's output is connected to the alternate (Bypass) input of the Main transfer switch. Should the Main UPS fail, its transfer switch will connect the load automatically to the output of the Backup unit .
A single system connected between the utility grid and the load.
An Offline or Line Interactive system that normally supplies the load from the utility mains.
A transfer switch that uses semiconductors (generally Triacs or SCR?s) as the power switching elements.
Interharmonic waveforms having frequencies lower than the fundamental.
Sharp high voltage increase (lasting up to 1mSec).
An electronic device or component used to protect electric circuits fromspikes and overvoltages. The surge arrester is generally connected in parallel to the input of the protected circuit. It limits the maximum voltage by absorbing excess energy.
A measure of maximal energy in joules a Surge arrester can absorb without damage.
An RMS increase in the AC voltage, lasting from half cycle to few seconds.
(Phase Lock or Sync.): Operation that causes an ac waveform to be at the same frequency and in phase with another waveform. Generally refers to synchronizing the output of the Inverter to the Utility mains, in order to allow smooth transfer of load from mains to Inverter and vice versa.
(Total Harmonic distortions): RMS value of all harmonics in a waveform (excluding fundamental) divided by RMS value of fundamental. THDV refers to Voltage waveform. THDI refers to Current waveform.
See @Earthed System.
See @Earthed System.
See @float voltage.
A term referring to the type of the UPS . Generally the topology is either offline (Sometimes called standby), Line Interactive or online .
Functional UPS module, which transfers the load from the output of the Inverter to the Bypass (fed by Utility mains or to other alternate source), and vice versa. The transfer from Inverter in Online type system is generally performed automatically in case of overload or whenever the output voltage deviates from a preset window. The AutomaticTransfer Switch will generally re-transfer automatically to the Inverter (see Retransfer)
Time interval from sensing transfer requirement until the load is transferred to alternate source.
A switching or other disturbance of the normal power voltage waveform, lastingless than half cycle. The transient can be either over-voltage or under-voltage.
A dimensional unit used to measure the height of equipment or racks. 1U equals 1.75 inches (44.45 mm).
(Uninterruptible Power Supply): An Electronic device connected between the Utility Power and electric consumers, comprising generally of filters, Rectifier, Battery, DC/AC Inverter, Transfer Switch and associated circuits. The UPS is intended to provide clean undisturbed stabilized AC voltage, within strict amplitude and frequency limits, to protect the consumerfrom any Utility Power disturbances and irregularities, including outages for a limited time dictated by the capacity of the Battery Bank. The term UPS refers generally to AC Static systems, Other types include DC and Rotary UPS.
A battery feeding the inverter. In most cases it is a VRLA type battery.
IEC 62040-3 Standard classifies UPS performance by 8-digit code:The first three digits classify output dependency of input mains in normal operation,(VFI-Voltage and Frequency Independent, VI ? Voltage Independent, VFD-Voltage and Frequency Dependant - See relevant Terms). The next two digits refer to output waveform: S-Sinusoidal for linear and nonlinear loads (THDV<8%), X ? Non sinusoidal with nonlinear loads, Y- Non-sinusoidal. The last three digits refer to output dynamic performance (including transients during transfer switch operation).
Standard IEC 62040-3 defines three standardized UPS systems:A. Passive Standby (Generally called Off -Line ).B. Active Standby (Generally called Line Interactive ).C. Double Conversion UPS (Generally called online ).
Conditions in which at least two phases at the output of a three-phase UPS have different (magnitude or PF) loads.
A voltage below the rated RMS value, generally for a duration of a few seconds (Shorter time undervoltages, see Transient or @Sag).
(Volt Ampere): Apparent power, defined as product of RMS Voltage and RMS Current
A system where the output voltage is Dependant on input Voltage and Frequency (IEC 62040-3). VFD class generally refers to Passive Standby (OFFLINE) systems. These are able solve the first three Power Line Disturbances (see term). The output from the Inverter is generally non-sinusoidal.The Dynamic classification is generally 3 due to power interruption during transfer switch operation.
A system where the output voltage is Independent from input Voltage and Frequency (IEC 62040-3). VFI class generally refers to Double Conversion online types. .These systems generally solve all 10 Power Line Disturbances (see term).The Output isgenerally sinusoidal for linear and nonlinear loads, with class 1 (No break) dynamic performance.
A system where the output voltage is Independent on the Input Voltage(IEC 62040-3), but depends upon the input frequency. VI class generally refers to Line-interactive type. These units are able to solve first five Power Line Disturbances (see term).
(Valve Regulated Lead Acid batteries) Sealed batteries with internal pressure, which causes the Hydrogen and Oxygen generated during charging to be turned back into water thus decreasing dramatically the amount of gassing through the valves and the need for water replenishing. The Electrolyte is immobilized using Gel or AGM construction. VRLA batteries can be installed in vented manned locations, are classified as non-hazardous, non spill-able, meet the requirements of air transportation (IATA), and practically do not require maintenance (Thus frequently called maintenance free batteries).
Actual power, equal to the product of fundamental (source frequency) harmonic RMS voltage, times fundamental harmonic RMS current, times cosine of the phase displacement angle between the voltage and the current.