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Glossary of Terms

Active redundancy - UPS with additional unit available to supply load.

Alternate power source - Supply from a generator

Backup time - Time during which the UPS can supply the rated load with nominal-quality power while the mains are down. This time depends on the battery and the efficiency of the UPS. Typical backup ranges from five minutes to several hours.

Battery on shelves - Battery cell installation system whereby the cells are placed on several vertically stacked shelves or racks made of insulating material.

Battery (recombination) - Battery with a gas recombination rate at least equal to 95%, i.e. no water need be added over battery life, usually called "maintenance free."

Battery (tier-mounted) - Battery cell installation system whereby the cells are placed on tiers made of insulating material

Battery (vented) - Battery cells are equipped with a filling port for distilled, demineralised water used to top up the free electrolyte.

Battery cells - The interconnected battery elements that supply electrical power created by electrolytic reaction.

Battery circuit breaker - Protective device to interface UPS with standby power source.

Battery Monitor - It incorporates software to calculate the real available backup time, predicts when batteries need replacement and a protection system against excessive discharges

BEM (Building and Energy Management) system - System used for control/monitoring of all building utilities and systems. It is generally composed of sensors, actuators and programmable controllers connected to a central computer or several computers, equipped with specific software.

BS (British Standard) - Label used to indicate compliance with British standards.

Bypass (manual) - Manually operated switch used to supply the load via direct connection to utility power during servicing of the UPS system.

Bypass (automatic) - In the event of an overload or an unlikely UPS problem, your application is still powered thanks to the automatic bypass module.

Charger - Device associated with the rectifier and used to supply the battery with the electrical power (DC current) required to recharge and/or float charge the battery, thus ensuring the rated backup time.

Circuit breaker (battery) - Protective device connecting the UPS to the stored power source.

Cos phi - A measure of the phase shift between the current wave and the voltage wave observed at the terminals of a load supplied with AC power at a given frequency.

Cos phi1 - A measure of the phase shift between the fundamental current wave and the fundamental voltage wave observed at the terminals of a non-linear load.

Crest factor (Fc) - Ratio between the peak current value to the rms current value.

Cubicle (parallel UPS unit) - Cubicle containing a rectifier/charger and an inverter. It is connected to one or several other identical cubicles and a bypass cubicle to make up a parallel UPS.

Cubicle (single UPS unit) - Cubicle containing a rectifier/charger, an inverter and a bypass. Connected to a battery, it operates alone, forming a single UPS. Compare with Cubicle (parallel UPS unit).

Current (float) - DC current that maintains the battery at nominal charge, corresponding the float voltage. This current compensates open circuit losses.

Current (inrush) - Temporary current observed in a network when electrical devices are energised, generally due to the magnetic circuits of the devices. The effect is measured by the currents maximum peak value and the rms current value it generates.

Current harmonics - The harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency.

Current loop (20 mA) - Transmission system used on certain devices and offering better performance than the RS232C. It provides a high degree of immunity to interference and is easy to implement, but has not been standardised.

Distortion (individual) - Ratio between the rms value of an nth order harmonic and the rms value of the fundamental.

Distortion (total) - Ratio between the rms value of all harmonics of a non-sinusoidal alternating periodic value and that of the fundamental. This value may also be expressed as a function of the individual distortion of each harmonic Hn = Yn /Y1

Earthing system - System for the interconnection and earthing of exposed conductive parts and neutral. There are three types of neutral system: IT, TN, TT.

Earthing system IT - Earthing system in which the neutral is isolated from the earth or connected to the earth via a high impedance and the various exposed conductive parts are connected to the earth via individual earthing circuits. An alarm must signal the appearance of a first insulation fault. The installation must be de-energized immediately in the event of a second insulation fault.

Earthing system TN - Earthing system in which the exposed conductive parts are interconnected and connected to the neutral. The neutral is connected to the earth. The installation must be de-energised immediately in the event of an insulation fault.

Earthing system TT - Earthing system in which the neutral and the exposed conductive parts are directly earthed. The installation must be de-energised immediately in the event of an insulation fault.

Electromagnetic compatibility - Possibility of a device to operate normally when installed near other devices, given the disturbances emitted by each device and their mutual sensitivities.

Filter (phase-shift) - Filter used to reduce, if necessary, the overall distortion due to the current harmonics injected into the mains upstream of a UPS by its rectifier-charger. Filtering is superior to that of a traditional filter of the L or C type.  

Float current - Current set to recharge the battery pack

Floating voltage - Voltage limit set on the battery charger

Fourier theorem - Theorem stating that any non-sinusoidal periodic function (frequency f) may be represented as a sum of terms (series) made up of: n a sinusoidal term with frequency f, called the fundamental frequency, n sinusoidal terms with frequencies that are whole multiples of the fundamental frequency, (harmonics), n a possible DC component. Where n is a whole number - (n = 1 corresponds to the fundamental and n > 1 to the harmonic of the nth order)

Harmonic - Sinusoidal term of the Fourier series expansion of a periodic function. The harmonic (or harmonic component) of the nth order is characterised by: -

  • Yn is the rms value of the given harmonic component,
  •  w is the angular frequency of the fundamental

phi is the phase angle of the given harmonic component at t = 0.

Harmonics (current and voltage) - All alternating current which is not absolutely sinusoidal is made up of a fundamental and a certain number of current harmonics which are the cause of its deformation (distortion) when compared to the theoretical sine-wave. For each current harmonic of order n and an rms value In, there is a voltage harmonic with an rms value Un. If Zsn is the voltage source output impedance for the harmonic of the nth order, then: Un = Zsn x In

High-frequency interference - (see Interference (high-frequency))

IEC (International Electrotechnical Commission) - Advisory organization that draws up international standards in the electrotechnical field.

Individual distortion - (see Distortion (individual))

Inrush current - (see Current (inrush))

Interference (high-frequency) - High-frequency parasitic current that is either conducted (electrostatic origin) or radiated (electromagnetic origin) by a device.

Inverter - UPS subassembly that recomposes a sine-wave output (regulated and without breaks) using the DC current supplied by the rectifier-charger or the battery. The primary elements of the inverter are the DC/AC converter, a regulation system and an output filter.

Inverter (off-line or stand-by) - UPS configuration in which the inverter is parallel-mounted to the load supply line and backs up the mains. This configuration offers a substantial cost reduction but is applicable only to low outputs, under 3 kVA, because it results in an interruption lasting up to 10 ms during transfer and does not filter inrush currents.

Inverter (on-line) - UPS configuration in which the inverter is in series mounted between the mains and the load. All power drawn by the load passes via the inverter. This is the only configuration used for high outputs.

IP (protection index) - (see Protection index (IP)

ISO 9000 - Standard defining procedures and systems used to attain an internationally recognized level of production quality. ISO 9000 certification is proof that the quality system effectively complies with the standard. Certification is carried out by an official organization (AFAQ), unaffiliated with either clients or suppliers or the company itself, and is valid for a three-year period with yearly audits and checks.

Load (linear) - Load for which voltage form and current form are similar. Voltage and current are related by Ohm's law U(t) = Z x I(t).

Load (non-linear) - Load (generally with a switched-mode power supply) generating major harmonic currents. Current wave form is different from voltage wave form. Ohm's law is not applicable. It can be used only with each harmonic.

Load power - Apparent power Pu that the UPS inverter supplies under given load conditions. It is less than or equal to the rated output Pn. The ratio Pu/Pn defines the % load of the inverter.

Micro-outage (or micro-interruption) - Total loss in the supply of power for 10 ms.

Monitor (system interface) - User interface on the Galaxy range of UPS systems. This interface includes an LCD alphanumeric display with two lines of 20 characters each and is used in conjunction with the Signal 4 interface.

MTBF (Mean Time Between Failures) - Mathematical calculation of the duration of normal operation of a repairable device between failures. The product, expressed in hours, is an indication on the reliability of the device.

MTTF (Mean Time To Failure) - Mathematical calculation of the duration of normal operation of a non-reparable device, i.e. for which a MTBF is not possible. The product, expressed in hours, is an indication on the reliability of the device.

MTTR (Mean Time To Repair) - Mathematical calculation (or statistical average if available) of the time required to repair a device.

Noise level - Acoustical decibel level of a source of noise, measured according to the applicable ISO standard.

Non-linear load - (see Load)

Off-line inverter (or stand-by) - (see Inverter)

On-line inverter - (see Inverter)

Output (rated) - Apparent power Pn that the UPS can deliver under given load conditions (power factor = 0.8).

Overall distortion - (see Distortion (overall))

Parallel UPS cubicle - (see Cubicle (parallel UPS unit))

Parallel UPS with redundancy - (see UPS (parallel with redundancy))

Parallel UPS without redundancy - (see UPS (parallel without redundancy))

Percent load - Ratio between the power Pu drawn by the load and the rated output Pn of a UPS system (Pu/Pn). Sometimes referred to as the load factor.

Phase-shift filter - (see Filter (phase-shift))

Power factor (l) - Ratio between the active power (P) supplied to a load and the apparent power (S) supplied to said load by an AC power supply.

Power source (alternate) - Backup source used in the event of a mains failure. The connection time and the duration of the source depend on the type of source used.

Power source (safety) - Power source for loads defined as critical by applicable safety regulations. This supply must not be affected by a mains failure and is generally separate from other supplies.

Protection index (IP) - Index indicating the capacity of an electrical device to resist environment conditions. It is made up of three digits (e.g. IP 205), each corresponding to a type of environmental risk. The higher the number, the greater the capacity to resist.

  • First digit (0 to 6): capacity to resist penetration by solid objects.
  • Second digit (0 to 7): capacity to resist penetration by liquids.
  • Third digit (0, 1, 2, 3, 5, 7, 9): mechanical strength.

PWM (Pulse Width Modulation) - Inverter high-frequency chopping technique using a means of regulation enabling rapid modification of pulse widths over a single period, thus making it possible to maintain the inverter output within tolerances even for non-linear loads.

Rated output – (see Output (rated))

Reactance (sub transient Uscx %, for generator) - Relative measurement (%) of the internal impedance of an AC generator during harmonic phenomena. This reactance, also called the longitudinal sub transient reactance of the generator, is sometimes identified as X"d. For most common generators, the value ranges between 15 and 20%. It can drop to 12% for optimized systems and to 6% for special devices.

Recombination battery - (see Battery (recombination))

Rectifier / Charger - UPS component that draws on the mains the power required to supply the inverter and to float charge or recharge the battery. The alternating input current is rectified and then distributed to the inverter and the battery.

Redundancy (active) - Parallel UPS configuration in which several UPS units with equal outputs are parallel connected and share the load. In the event one UPS unit fails, the other units pick up its share without any interruption in the supply of power to the load.

Redundancy (standby) - UPS configuration in which one or several UPS units operate on stand-by, with no load or only a partial load, and can immediately back up a faulty UPS unit by no-break transfer of the load, carried out by a static switch.

Reliability - Probability that a device will accomplish a required function under given conditions over a given period of time. Rms value of AC current with harmonics The rms value Yrms of a non-sinusoidal alternating current may be determined on the basis of the individual harmonic currents: where Y is the rms value of the fundamental.

RS232C (Recommended standard RS232C) - Standard defining the communication circuits between devices for synchronous and asynchronous transmissions on the following types of lines: two-wire, four-wire, point-to-point, telephone lines and local links with short cables. Though the standard covers only transmissions over distances up to 15 meters, it is often possible to ensure correct transmission over greater distances using high-quality shielded cable in a reasonably satisfactory electrical environment. Most terminals and devices on the market can implement this transmission standard.

RS485 (Recommended standard RS485) - This standard is similar to RS422A except that the number of possible links is greater and up to 32 senders may be interconnected to as many receivers. This system is particularly designed for local-area networks.

Safety installation - Installation supplying electrical equipment which may have a direct effect on the safety of users and must therefore remain energised even in the event of a mains failure. In general, characteristics concerning the power supply and conditions for transfer to the safety source for such electrical equipment are covered by applicable regulations.

Safety power source - (see Power source (safety))

Single UPS cubicle - (see Cubicle (single UPS unit))

Single UPS - (see UPS (single))

Standby redundancy - (see Redundancy (standby))

Static bypass switch - Power-electronics device that can be used to switch from one source to another without interruption in the supply of power. In a UPS, transfer is from Mains 1 to Mains 2 and back. Transfer without interruption is possible due to the fact that there are no mechanical parts and the ultra-fast switching capabilities of the electronic components.

Sub transient reactance of generator (Uscx %) - (see Reactance (subtransient Uscx %, for generator))

Thevenin generator - For a given load, it is possible to consider the power supply as a voltage generator, referred to as a Thevenin generator, made up of a perfect voltage Uo generator, in series with an internal impedance Zs: n Uo is the voltage measured across the load terminals, given that the load is to be disconnected (load terminals forming an open circuit), n Zs is the equivalent impedance as seen from the load terminals (again considered an open circuit), obtained by short-circuiting the upstream voltage generator(s).

Tolerance in % - Limit for allowable variations for a given quantity, expressed as a percent of the rated value.

Transformer short-circuit voltage (Uscx %) - Relative measurement (%) of the internal impedance of a transformer. This short-circuit impedance is commonly called the short-circuit voltage because it is measured during a short-circuit test (shorted secondary winding subjected to a current set to In). For most common three-phase transformers, this value ranges between 3 and 6%.

Underwriters Laboratories (UL) - A non-governmental, non-profit certification organization in the United States in which not only government authorities are represented, but also consumer groups, "export" services, research, etc. Following certification, a product may bear the UL label.

UPS (Uninterruptible Power Supply) - An electrical device providing an interface between the mains power supply and sensitive loads (computer systems, instrumentation, etc.). The UPS supplies sinusoidal AC power free of disturbances and within strict amplitude and frequency tolerances. It is generally made up of a rectifier/charger and an inverter together with a battery for backup power in the event of a mains failure.

UPS (parallel with redundancy) - A UPS made up of several parallel-connected UPS units with equal output ratings (P) and each equipped with its battery. If one unit fails, one or several of the others pick up the resulting excess load. If a UPS has a rated output n x P and is made up of n + k units, k is the level of redundancy for the entire set of n + k units. Units with equal output ratings (P) and each equipped with its battery, for large loads. The total output is equal to the number of units multiplied by their individual output (n x P). In this configuration, no UPS unit is redundant.

UPS (single) - A UPS made up of one single UPS unit (rectifier/charger, inverter and bypass) and a battery.

Vented battery - (see Battery (vented))

Voltage (float) - DC voltage applied to the battery to maintain its charge level. This voltage depends on the type of battery, the number of cells and the manufacturer’s recommendations.

Voltage harmonics – (see Harmonics (current and voltage))