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Technical Dictionary



Active Power

See also: Power Factor

Alternate Current

This is an electric current that is alternately a positive and negative. Usually (public mains) has a sinusoidal shape.

Alternate Voltage

It’s a voltage that has alternately a positive and a negative value. Typically mains have a sinusoidal shape.
The mains output varies between countries: 100 V AC in Japan, 240 V AC in England, 230 V AC for Europe and in USA it’s 110 VAC.
The frequency in Europe is 50 Hz and 60 Hz in USA. In special applications, for ex. in aircrafts, the frequency is 400 Hz and some computers require 415 Hz.

Apparent Power

See also: Power Factor



Devices that, through chemical reactions, is capable to store electricity.
Unlike dry sealed cells, they can be charged several times. UPS uses currently sealed (do not pour the electrolyte and need no maintenance) lead acid batteries (other technologies are more expensive) for stationary applications (car batteries are not suitable). These batteries have a lifetime average of 3 to 5 years, depending on the temperature and the number of cycles of charge/discharge (from 100 total discharges to 1000 partial discharges).


This is a device that provides an alternative path for power supply.



See also: Mains Failure



Equipment used for batteries recharge. There are several types: simple domestic chargers to recharge car batteries; traction chargers, to load electric forklift batteries; chargers/power feeders for telecommunications.

See also: Power FeederRectifier

Continuous Current

This is a current with one-way, like batteries loading and unloading current.


See also: Power Factor



It’s the relationship between the effective value (RMS) of the harmonic content and the total effective non-sinusoidal periodic function value.
In the case of UPS, reflects the deviation from the output voltage in relation to a perfect sinusoidal wave shape. Typical values for resistive loads ranging between 1 and 5%.


See also: Mains Failure



Relationship between the energy that the equipment provides to load and the energy it consumes from the mains.

For example, if a given UPS feeds a load of 400W and has a efficiency of 80%, it consumes from mains 400/0.8 = 500W.

This means that the UPS dissipates itself 100W to the environment.

Electronic Protections


Initials for Electromagnetic Interference.
Refers to high frequency disturbances produced by electric equipments when they are working.


Galvanic Isolation

Mains do not provide a perfect voltage, free of problems (see Mains Failure). To avoid the effects of electrical noise and voltage differences that appear between distant points of the same facility due to consumption of equipment connected to it, you can use the galvanic isolation.

Galvanic isolation is the transfer of electricity between two points without connecting wires. The simple electrical device capable of providing galvanic isolation is the transformer.

Some UPS also provide galvanic isolation between the mains input and the output to the load.

See also: Safety



Input Current

In the case of a UPS, it’s the maximum effective (RMS) current drawn from mains. It is interesting to the selection of technical devices such as fuses and circuit breakers and for sizing of the cabinet.

Input Frequency

Number of times per second, that the mains supply voltage repeats its wave cycle. Cycle is called the shortest time when all the instantaneous values of the tension referred are met. The unit of measurement is Hertz (Hz) which corresponds to the number of cycles per second. The frequency of the network is maintained with tight tolerance around 50 Hz or 60 Hz (depending on the specification of the mains).

Input Voltage

RMS voltage value allowed at the entrance (the nominal value and upper and lower limits) that allows the equipment to work without changing performance.

Instant Current Limitation

When the loads consume high currents during the time they are connected, and / or on the peak of the sinusoidal wave, as is the case of computers, it must be provided for a short time all the energy that will be consumed until the next peak voltage. Because of this, the peak current could reach values that would be destructive to the UPS. However there is an electronic protection which limits the maximum instantaneous current, this current is several times the current that would be consumed by a resistive load such as an incandescent lamp.


See also: Safety



It’s equipment that generates alternate voltage from a continuous voltage.

It’s used to power equipment using 230 V AC in fixed installations where the voltage supply is generally continuous, either to ensure continuity of supply in critical applications such as telecommunications, PABX, etc., or because the source of energy generates continuous voltage, as the applications of alternative energy such as wind and solar.
In mobile applications is used for, from a battery, for ex. a car, or boat, or bus battery, feed measuring equipment or other equipment such as videos, computers and electronic scales.


Limitation against Short Circuit

UPS may be subjected to a short circuit without any damage or merge any fuses. Typically, after the removal of short-circuit and after a few seconds, the UPS begins its normal operation.

Limitation of Active Power

As typical loads have a power factor lower than unity, limiting output current is not enough. There is available in some more sophisticated units an electronics limitation to the maximum Active Power. In most of the UPS this limitation is by fuses or circuit breakers.


Mains Failure

There are several types of mains disturbances:

  • Pulse (or peak) – momentary voltage increase (less than 1ms)
  • Noise – pulses of oscillatory nature of high frequency.
  • Micro power cut (or dropout) – total voltage loss between 1ms and 1s
  • Power Cut (or outage) – total loss of voltage lasting longer than 1s
  • Surge – Voltage surge over the nominal voltage longer than 2.5s
  • Brownout – Voltage under the nominal voltage longer than 2.5s

Manual By-Pass

By-pass that is normally used for maintenance purposes, allowing the load to be powered by mains electricity when the UPS is off (ex.: For battery replacement, cleaning, etc.).
It can be found in units with or without static by-pass.

Mechanical Protection

The Index of Protection IP defines the protection of the equipment’s box.

The first number sets the maximum size of the body that can penetrate the box; the second defines its behaviour for liquids and the third number (seldom used), the impact energy.

First digit, protection against direct contact and external bodies input:

  • 0 – no protection;
  • 1 – against bodies greater than 50 mm (ex. unintended hand contact);
  • 2 – against bodies greater than 12 mm (ex. fingers);
  • 3 – against bodies greater than 2.5 mm (ex. tools, clips, hairpins);
  • 4 – against bodies greater than 1 mm (ex. small wires);
  • 5 – against harmful dust deposit;
  • 6 – total protection against dust deposits.

Second digit, protection against liquids penetration:

  • 0 – doesn’t have;
  • 1 – against a vertical drop of water droplets (condensation);
  • 2 – against falling drops to 15 degrees from the vertical;
  • 3 – against falling drops to 60 degrees from the vertical (rain);
  • 4 – against water projections in all directions;
  • 5 – against high pressure water projections in all directions;
  • 6 – against water projections equivalent to a wave;
  • 7 – against immersion;
  • 8 – submersible equipment in agreed conditions.

Third digit, impact energy of a body:

Thus, IP20 means that do not penetrate bodies (spherical) greater than 12 mm (ex. fingers) in diameter and there can not be water projection.

Micro Power Cut

See also: Mains Failure



See also: Mains Failure


Output Current

In the case of a UPS, it’s the maximum effective (RMS) current that can be supplied to the load. This value is not usually specified, but instead the power in W or VA.

Output Frequency

Number of times per second, that the output voltage of a UPS repeats its wave cycle. The frequency of the output voltage is usually equal to the mains input voltage’s frequency. The tolerance of the output frequency depends on the equipment and is usually equal to 50 Hz (or 60 Hz) ± 1%.

In special cases, when the equipment to feed requires a different frequency from the one of the mains, you can use a UPS to generate the frequency output, and enable the use of such equipment.

Output Voltage

RMS value of the voltage generated by the equipment (nominal and tolerance) under various loading conditions (for ex., between 0 and 100% or only between 50 and 100%), with mains voltage and only with the battery voltage.



See also: Mains Failure

Power Factor

If the current of a load is sinusoidal and there is no gap between the voltage and current (as it’s the case of an incandescent lamp), the power consumed is given by the product (V x I in RMS).
If the current of a load is sinusoidal and there is mismatch between the voltage and current (as it’s the case of a fluorescent lamp), the power consumption is given by the product of voltage by apparent current consumption (the current that would measure a whether interclass ammeter), times the cosine of the lag angle Ø.

For example, if the current measure is 1A and the lag angle is 45°, which corresponds to a cos 45º = 0.707, so we have that Apparent Power is equal to:
A.P. = 230V x 1A = 230 VA
However, Active Power, i.e., the true power in watts, will be:
P = 230V x 1A x 0.707 = 162.6 W
If, for example, the load is the power supply of a computer, the power consumed is not sinusoidal, but in a pulsating in the crest of the sinusoidal. In this case it’s incorrect to speak of cos Ø, but in Power Factor.
Both cos Ø, whether the FP, are less than or equal to unity. This means that the smaller this value more is the current that must be provided for the same power consumption.
In the case of UPS, is typically considered a PF of 0.7 because computers present consumptions with a PF of this order, and may even reach 0.6.

Power Feeder

Equipment used to feed loads with electric direct current, namely PABX, while they keep charged batteries in buffer.
In case of blackout, the batteries keep the device powered.
The output voltage must have a ripple in accordance with the CCITT standards.

See also: Charger; Rectifier

Pseudo-Sine Wave

Same as: Square Wave.


See also: Mains Failure



Equipment that rectifies the voltage from the mains, i.e., transforms alternate voltage into continuous voltage. Although the terms rectifier, feeder and charger are sometimes used indiscriminately, as all these equipments rectifies mains voltage, the equipments are very different.

The term rectifier applies more properly to the devices used, for example, in electroplating, for currents that reach thousands of amperes without much demand for filtering (purity) of the supplied voltage.

See also: Power Feeder, Charger

Repetitive Peak Power

The loads that have switching power supplies, uses a pulsating current mode, only at the peak of the sine wave. UPS or Inverter must be able, during that short time, to provide all the energy that is consumed throughout all the half cycle. This peak current is much higher (about three times) that the current that would correspond to the same power if it was consumed in a sinusoidal mode, as in the case of an incandescent lamp.

The product of the peak voltage by the peak current, is called Repetitive Peak Power (since it is repeated every half cycle).

If the UPS does not have the ability to provide a high Repetitive Peak Power, the sinusoidal voltage is very low at the crest not feeding properly the load.

Response Time

Time that the unit (UPS, Power Feeder, Stabilizer), after a sudden change of consumption in output, leads to correct the momentary change of the voltage, within certain values.


Alternate voltage, usually low, which is found added to continuous voltage in Power Feeders and Rectifiers.


Initials for Root Mean Square – Designates the Effective Value of a quantity (voltage, current, etc.).

In the case of a sine wave, corresponds to the peak value (325 V) divided by the square root of 2 (1.414). The obtained value (230 V AC) is the value that provides the same amount of energy that of a continuous voltage with a constant value of 230 V.



Any appliance must be harmless to the user. Nevertheless, its design must ensure safety standards that involve not only electrical aspects (eliminating the dangers of electrocution) as technical and mechanical (high temperatures, mechanical stability, etc.).

All these aspects are defined in safety standards, highlighting the IEC950.

Sine Wave

Wave whose form is a sine. The mains RMS voltage is 230 V AC and the peak value (voltage at the crest of the wave) is of 325 VAC.

Square Wave

It’s the most used and typical waveform used by off-line units. It has three levels of voltage (positive voltage, 0 volts and negative voltage). It is a wave economically and technologically easier to generate than a sine wave.

This waveform generates high frequencies (harmonics), which heats electric motors and transformers and does not hold generally the same relationship between the effective value (RMS) which should be 230 VAC and the peak value which should be 325 V.

This waveform, in order to confuse the consumer, receives from some manufacturers, a series of abusive names:

  • Modified Sine Wave;
  • Trapezoidal Wave;
  • Pseudo-Sine Wave;
  • PWM modulated Pseudo-Sine Wave
  • Etc.


It’s electronic or electromechanical equipment (with a varying motor, in this case) to correct deviations, surges and sags of the mains voltage in relation to the nominal value.

Static By-Pass

This is a By-Pass that uses solid state devices (Thyristors, Triacs and Transistors) for power transfer. In a UPS is used to increase overall reliability of the equipment, providing power to the load by mains, in the event of failure of the Inverter or violent overflow. Depending on the construction, the transfer between the inverter and the mains is done without interruption.


See also: Mains Failure


This word means in everyday language, a technology used in power converters.
To transfer power through a transformer, it can run on the mains frequency (50 Hz or 60 Hz) or at a high-frequency, ex. upper than 20.000 Hz (20 kHz) using electronic devices to get this high frequency.
The advantages of this technology are the small size and weight, the silence (the acoustic noise it generates is inaudible) and its low cost.
The disadvantage is the higher complexity of the project.


Thermal Protection

Electronic or mechanical device (thermostat) to protect equipment in case of over temperature (fan damaged or blocked air vents, high ambient temperature, etc.).

For protection normally acts switching off the equipment.

Transfer Time

In the case of off-line units, it’s the time between a mains failure and the replacement of the output voltage generated by the inverter.

Should be taken into account the time of detection of mains failure coupled with the switching time of the used device (relay or other).

The opposite case, passage of the inverter to the mains is less critical.

For on-line units with by-pass the transfer time is zero, since the switching between the inverter and the mains, and vice versa, is provided by solid state components (Thyristors), which switching is, to all practical purposes, instantaneous.



Uninterruptible Power Supply – Equipment designed to keep critical loads (computers, telephone exchanges, medical equipment, etc.) always operating during a mains power failure and to protect them from problems of power supply.