Glossary Emergency Power Supply


Active power is the electrical power that is actually applied to the load, and is the product of voltage and current and phase shift (cos phi) . It is available for conversion into, for example, mechanical, thermal or chemical power. Its unit is the watt (W).

The power factor or active power factor (lambda) indicates the ratio between the amount of the active power to the apparent power. It is always between 0 and 1.

Alternating current is the name given to the type of electric current that periodically alternates its direction of flow (polarity) and current strength. Typically, current and voltage levels oscillate in the form of a sinusoidal wave such that the positive and negative values are complementary to each other at zero over averaged time. This is the type of current supply that is supplied as standard in Germany.

The availability of a technical system is an indication of the probability of the system being able to provide the power output required of it within a certain period. It is divided into several classes, from simple availability (99.5%) to high availability (99.9% and above) and on to non-stop availability (100%). The values follow from the mean time between failures (MTBF) and the mean time to repair (MTTR). The formula is: MTBF/(MTBF + MTTR).

Backup time (also known as bridging time) denotes the length of time for which a UPS system is able to supply the connected load in the event of a power loss.

A balanced load denotes a uniform load distribution in all conductors of a multiple-phase system (e.g. a three-phase current system).

The unit BTU defines the heat energy that is required to heat a British pound of water by 1 degree Fahrenheit. 1 BTU = 1,055 Joule (J)

See Wiring diagram​​​​​​​

Circuit feedback occurs when an electrical load influences the mains network that is supplying it. There can be various causes of this, ranging from short-term interruptions to voltage drops to harmonics from the load.

In electrical engineering, a converter transforms the form of a current feed (either direct or alternating current) into the other respective form. An example of a converter in emergency power engineering is a switch mode power supply.

The crest factor, also known as the peak factor, is an electronic signal value. It describes the ratio of the peak value (Vss) to the effective value (Veff) of an oscillation.

Electric current denotes the targeted movement of electrically charged particles such as electrons and ions. It is a physical unit used in electrical engineering, and is stated in amperes or amps (A).

Direct current denotes an electric current whose strength and direction are constant (do not change). It is generated either by employing a rectifier or by using (rechargeable) batteries or a DC generator.

DC supply systems provide a secure power supply. They provide loads with a constant direct current.

Downtime is the time that a plant or system is not available or operational.

Energy efficiency is an indication of the ratio between energy applied and energy obtained; it is therefore a quantitative expression of the efficiency of a machine’s use of energy.

See Load, electronic​​​​​​​

Electromagnetic compatibility denotes the ability of a device, plant or system to operate in such a way that no electromagnetism is created, the effects of which would create a disturbance to other devices.

An emergency generator, also referred to as a general replacement power supply, consists of at least one emergency current generator unit or some other substitute current source.

An emergency generator is a device that generates electricity in one of several ways for the purpose of creating independence from the standard electricity grid. The generator is primarily driven by petrol or diesel (in the form of a combustion engine).

An emergency power supply ensures the availability of backup power in the event of a failure of the public power supply. Depending on the area of application, different systems are used - from simple emergency generators to diesel UPS systems to complex UPS system architecture.

Failure rate is a key indicator of a product’s reliability. It states the probability in percentage terms of a product suffering failure within a particular time interval.

See Downtime​​​​​​​

The frequency is the number of oscillations that an alternating current displays over the duration of one period. The unit is the Hertz (Hz = 1/sec.) In EMEA regions, it is generally 50 Hz (the frequency of the public electric mains supply).

See Backup time​​​​​​​

This term refers to the possibility of exchanging system components and modules such as a UPS module during ongoing operation without disconnecting the critical load from the UPS.

An inverter converts a direct current voltage into an alternating voltage.

An electronic load (e.g. a switch mode power supply) in the context of an emergency power supply is an electric component or electric device that is connected to a UPS system and is protected by it. In general, however, a load is understood as an electric component or an electric device in which electrical energy is converted to some other form of energy. Companies and private households are also referred to as electrical loads or consumers in the context of electricity supplies.

A mains switchback mechanism is an automatic internal bypass device that switches loads directly and without interruption to the mains in the event of an outage or overload of the inverter, overload of the protected busbar etc.

Mean time between failure is an indication of the probable time period until a system or a system component breaks down again as a consequence of malfunction.

The mean time to repair indicates the time between the occurrence of a malfunction and restoration of the system.

Modbus is an open communication protocol that enables the exchange of data between a master and several slaves. Today, it is the most common serial interface connection to be used in industrial equipment such as computers and other technical systems. It enables multiple devices from a network to communicate with each other quickly and simply.

If the output of a three-phase UPS (uninterrupted power supply) has a 100% non-linear driving capability, this indicates that the output can only be subjected to full load on one phase.

The normal line is the standard mains for general current supply without any emergency power supply.

See Active power factor​​​​​​​

Cos phi is the power factor that indicates the ratio of active power to apparent power in sinusoidal currents and voltages (cos phi= P/S). It may be positive or negative, depending on whether the loads are inductive or capacitive. 

A protected busbar denotes the part of a voltage supply that continues to receive power from an emergency backup system in the event of power outage.

A rack unit is the unit employed in switching cabinets (electronic equipment housings, 19” racks). It indicates the height of the device or the equipment housing, whereby 1 unit (1U) corresponds to 1.75 inches (or 4.5 cm).

Reactive power is the surplus electrical power which is drawn and fed back to the mains network after a time delay. It oscillates backwards and forwards between the load and the generator and is needed for building up the voltage. Its unit is the volt-ampere reactive (var).

RS-232 is a standard serial interface from the 1960s; it is nowadays referred to as EIA-232. It was formerly used for modems, printers and terminals, among other devices, and is meanwhile used in PC equipment and entertainment electronics. The data is transmitted in word units. Each data word consists of between five and nine bits.

A rectifier converts alternating current to direct current.

Redundancy in engineering denotes the existence of additional similar plant components and systems that are not required during disturbance-free operation. They stand ready for use in the event of the loss of operational reliability, when they take over the service of the respective components.

The network is supplied by a backup power supply in the event that the general power supply is lost.

Self-clocking refers to a clock frequency that a device generates itself. Self-clocking in emergency power systems is of particular relevance when there is a loss of mains power. An example: Normally, an inverter is clocked by the mains, when this is present. In the event of a loss of mains power, loads are then able to switch over at any time without any interruption. When the mains power is lost, the inverter begins to self-clock to enable it continue supplying a frequency of 50 Hz.

The Simple Network Management Protocol (SNMP) is based on the User Datagram Protocol (UDP) and serves to monitor, control and configure network components such as routers, firewalls, servers and computers.

See Wiring diagram

A switch mode power supply is a power converter that transforms a non-regulated input voltage into a constant output voltage.

See Three-phase current​​​​​​​

See Three-phase current​​​​​​​

Three-phase current, also referred to colloquially as high-voltage current, is a special form of alternating current. It consists of three distinct alternating currents arranged in shifted phases of 120° from one to the text.

A trickle charge is the amount of charging required to maintain a stationary battery’s charge at full level. It thus balances out the battery’s self-discharge.

Uninterrupted power supply, see UPS system

As its name suggests, a UPS system provides an uninterrupted supply of power. It is connected between the electricity feed line of the equipment, machines and plants to be protected and ensures the continued supply of electric current to critical electrical loads in the event that the power supply is lost. Three classes of such devices have established themselves on the market, each with a different operating mode: voltage and frequency dependent (VFD), voltage independent (VI) and voltage and frequency independent (VFI). They are distinct from emergency generators (general backup power suppliers). These display a brief interruption to the power supply when switching over.

Electric voltage is a physical quantity in electrical engineering and is stated in volts (V).

The VFI classification is contained in the IEC 62040-3 standard, which categorises UPS systems into three levels. The VFI type of UPS system operates in offline mode, see Voltage Frequency Dependent UPS systems.

The VI classification is contained in the IEC 62040-3 standard, which categorises UPS systems into three levels. The VFI type of UPS system operates in line interactive mode, see Voltage Independent UPS systems.

The VFI classification is contained in the IEC 62040-3 standard, which categorises UPS systems into three levels. The VFI type of UPS system operates in online mode, see Voltage Frequency Independent UPS systems.

Voltage frequency dependent (offline) UPS systems are dimensioned for use in private locations, home offices, and systems with relatively low power. They only provide protection against mains power cuts and brief fluctuations and are not able to detect disturbances shorter than 4 milliseconds. 
The loads are generally supplied with mains voltage while the batteries in the UPS system are simultaneously charged. As soon as a power cut or severe mains fluctuations occur, the UPS system immediately switches over automatically to battery operation. This makes the loads dependent on both voltage and the frequency of the mains supply.

Voltage frequency independent UPS systems differ from VI and VFD systems in terms of their functional principles. They convert the voltage twice and therefore offer the highest level of protection against power losses, voltage surges, and other disturbances. The alternating input voltage is first transformed to a DC voltage and subsequently converted back to a stable alternating voltage. In normal cases, the inverter draws its current directly from the rectifier and only when there are strong fluctuations in the mains current or there is a power cut is the current obtained from batteries. The loads themselves have no direct connection to the mains network. This makes them independent of both the mains voltage and the mains frequency.

A voltage independent (line interactive) UPS system operates basically the same way as the voltage frequency dependent type of UPS system. The difference is that this type of system additionally checks the mains voltage and regulates it to an acceptable level within certain tolerance limits. If the fluctuations are excessively high, the alternating output voltage is generated by the inverter with energy from the batteries. This means that the loads are not dependent on the mains voltage.

A wiring diagram is a simplified, non-scale representation of a system. It is also referred to as a circuit diagram, schematic diagram or single-line diagram. It is used as a basis for dimensioning.