UPS knowledge

A uninterruptible power supply protects connected consumers from power failures, voltage fluctuations and disruptions in power quality. The appropriate design depends on the load, protection requirement, Runtime, environment and service concept.

Why UPS knowledge is important

A UPS is not only selected based on power in VA or watts. The decisive factors are the application, the risk of failure, and the desired one Runtime, the design, the condition of the power supply and the question of whether maintenance must be possible without switching off.

The requirements differ depending on the consumer group. Servers, networks, telephony, access systems, cash registers, controls, machines, measuring stations and security technology react differently Switchover time, Interruption time, voltage drops or Transients.

For a reliable selection, terms such as: VFI, VI, VFD, bypass, battery or Power factor can be clearly distinguished.

Key terms at a glance

The most important terms are linked directly to the lexicon below. The detailed definitions for technical selection, product comparison, project planning and service are available there.

UPS selection begins with application

Before selecting a system, it should be clear which consumers will be protected. A single server has different requirements than network, telephony, access systems, cash registers, controls, machines, measuring stations or security technology.

The required output power is not just the sum of the watts. Also Load Power Factor, Crest factor, inrush currents, reserves, non-linear power supplies and later expansions influence the design.

UPS classification based on operating behavior

The classification according to EN 50091-3, IEC 62040-3:1999 and VDE 0558 Part 530 describes the operating behavior of a UPS system. The aim is to create a common basis so that users can assess manufacturer information in a more comparable way.

The code doesn't just describe a marketing term like Online UPS or Line-interactive. It classifies how independent the UPS output is from the input, what curve shape the output voltage has and how the system behaves in the event of load jumps or operating mode changes.

Classification code

A typical code is VFI-SS-111. It consists of three parts.

Network dependency: VFI, VI and VFD

VFI - Voltage and frequency independent

At VFIsystems, the UPS output is independent of the input voltage and input frequency. Voltage and frequency changes in the network are decoupled from the output within the permissible limits. Common names are Online UPS, Double conversion, Continuous operation, permanent converter or double converter.

VFI typically makes sense when sensitive IT, controls, process systems or locations with fluctuating network quality need to be protected. In a double conversion UPS the rectifier the intermediate circuit, while the inverter provides the output voltage. A precise technical inspection is also useful for generator operation or complex load profiles.

VI - Voltage Independent

At VIsystems, the UPS output depends on the mains frequency, but the voltage is stabilized within defined limits. Common names are Line-interactive, Delta Conversion, Single Conversion or active tracking operation.

VI can be suitable for less critical consumers, network components or workstations if short switching times are acceptable and the network quality is sufficiently stable during normal operation.

VFD - Voltage and Frequency Dependent

At VFD-Systems output voltage and output frequency follow the changes in the network. Common names are Offline UPS, Standby UPS, passive tracking operation or standby operation.

VFD is more suitable for simple individual consumers and less critical applications. The suitability for server rooms, controls or production areas should be checked carefully.

Output voltage waveform

The second group of letters describes the shape of the output voltage. The first letter applies to normal operation or occasional bypass operation, the second letter applies to battery operation.

The shape of the curve is particularly important nonlinear loads, switching power supplies, motors, transformers or devices with high current peaks. Terms like Harmonic, Harmonic distortion and THD describe how much a voltage deviates from the ideal sine.

Output behavior during switching and load jumps

The third block of numbers describes the worst behavior of the UPS output during operating mode changes and load jumps. The first digit applies to the change in operating mode, the second to linear load jumps and the third to non-linear load jumps.

Practically relevant here Switchover time, Interruption time, control speed and the behavior of the inverter in the event of sudden load changes.

The actual behavior in a specific application also depends on the load profile, non-linear loads, reserve, power quality, cabling and environment. Critical systems should therefore be technically designed and not just selected based on an abbreviation.

Battery, runtime and recharge

The battery is the energy storage of the UPS. She takes care of him Inverter, if the AC power supply fails. The desired ones count for the design Runtime, load power, DC link voltage, battery type, ambient temperature and aging.

The specified one Battery capacity is not automatically the usable runtime in a UPS application. With short discharge times, the energy that can be extracted can deviate significantly from the nominal capacity. Therefore, running times are calculated based on manufacturer data, discharge curves and safety reserves.

Those too Recharge time is important. After a longer power failure, the full runtime is only available again when the battery is sufficiently charged. An adapted one Float charge supports lifespan.

Check the runtime specifically

The is available for a first selection UPS runtime calculator ready. It connects load, target time, reserve, battery status and temperature with the visible ERREPI shop entrances.

The result is an orientation for the next selection or offer question. Technical testing is still required for critical loads, long run times or external battery packs.

Bypass, maintenance and serviceability

A Bypass is an alternative current path to rectification and alternation. It can become relevant in the event of an error, overload or for maintenance work. Depending on the application, a distinction is made between internal switching, static bypass and external service bypass solutions.

What is important for critical consumers is whether a UPS can be serviced or replaced without switching off the load. Play here redundancy, Multi-block systems, Hot Swap, external bypass modules and a coordinated service concept.

Interfaces are also important in IT and network environments. SNMP, dry contacts, RS232 or network cards can support notifications, controlled shutdown and remote monitoring.

Load behavior and network quality

A UPS not only has to deliver enough power, but also has to be able to cope with the electrical behavior of the consumers. Switching power supplies, frequency converters, transformers, motors or controls can generate high peak currents, distortions or feedback.

For the evaluation are Power factor, Crest factor, nonlinear load, Grid interaction, Harmonics and Transients decisive. In some cases, filters are a Isolation transformer or galvanic isolation sensible.

Environment, efficiency and operation

The installation location influences operational safety and service life. Installation height, temperature, ventilation, dust, accessibility, noise levels, discharge options and subsequent battery replacements should be considered early.

The Efficiency affects power loss, heat and operating costs. Energy saving modes like Eco mode or HE mode can improve efficiency, but must match the protection requirements of the application.

In addition to the UPS itself, monitoring, maintenance, availability of spare parts and clear responsibilities are also important for high operational reliability. Terms like MTBF, MTTR and Availability help to discuss technical risks in a comprehensible manner.

Assignment of our UPS series

The following overview assigns the usual names to the ERREPI product families. It serves as orientation and does not replace the concrete technical design.

Planning questions before an offer or project

These points are helpful for a reliable offer or project planning:

• Which consumers are critical and which can be switched off in the event of a power failure?
• What load data is available: watts, VA, power factor, inrush currents and reserve?
• What runtime is really required: orderly shutdown, generator start or continued operation?
• Is an external bypass or serviceable design without load shedding required?
• Are there any special requirements regarding the battery, installation space, discharge, weight, temperature or fire protection?
• Should monitoring, SNMP, event notifications or automatic system shutdown be integrated?
• What service requirements exist: maintenance contract, battery replacement, availability of spare parts or response time?

The more of these points are clarified in advance, the better the UPS system, battery, accessories and service scope can be coordinated.

Further pages

Individual terms can be used in UPS lexicon be deepened. For the selection in the specific project are also Consulting and project planning, the Store, the Service area and the UPS criticality analysis the appropriate next entry points.