Modular UPS Systems

Modular UPS systems have a standard module size and a range of frame sizes into which a set number of UPS modules can be installed. The modules are typically plug and play and can be arranged in an N+X parallel or capacity arrangement. Modular UPS are very efficient with on-line operational efficiencies of 96% or more achieved using the latest power electronics and intelligent controls that place unused modules into a ‘sleep mode’. Modular UPS systems may also use plug-in battery cartridges or be connected to an external battery cabinet or battery stand arrangement.

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Modular UPS Specifications

UPS modules are typically rated at Unity Power Factor where kW=kVA i.e. 25kW=25kVA. Once the total load capacity (in kW) has been determined the total number of power modules can be calculated:

Load kW / UPS module size = number of UPS modules required

Additional UPS modules may then be added to achieve N+X parallel ups redundancy. The most common practice being to add one further module for N+1 redundancy.

Once the number of UPS modules has been determined the next step is to select a UPS frame size. A typical modular power systems manufacturer may offer two or three frame sizes. The frame can be fully or partly populated (with UPS modules). Best practice is to allow one to two slots (if available) for future expansion.

The modular UPS frame will incorporate the necessary electrical switchgear to connect the UPS to the local mains power supply and to connect the output from the UPS modules as a system to the connected load(s). The UPS frame should also incorporate an overall static bypass and maintenance bypass switch arrangement. These switches may also be built-into some UPS modules.

Modular uninterruptible power supplies tend to have a price premium over mono-block UPS systems including transformer-based and transformerless designs.

For individual product specifications please refer to the individual products and their specification datasheets.

Scalable and Resilient UPS

Modular uninterruptible power supplies tend to be transformerless UPS allowing the individual modules to achieve high operating efficiencies of up to 97% or more in on-line mode and up to 99% in line interactive or ‘eco’ mode. The UPS modules are designed for hot-swap and when connected into a UPS frame are automatically detected and an initialisation process started. Only if the UPS modules passes the start-up and self-test procedure is it allowed to power the critical load. This flexibility means that a modular power UPS can be ‘right sized’ for the load in operation at any given time and provide N+X resilience.

Modular Energy Efficiency

Modular UPS system architectures are based on a frame size, designed to take a maximum number of UPS modules. A site can choose to install a sufficient number of modules for the load profile or add in extra modules for N+X redundancy.

When there are more modules than are required to power the load, a modular power system can increase its operational efficiency by ‘sleeping’ redundant modules. If the mains power supply fails, all the modules in ‘sleep’ mode are activated. After the mains power supply has stabilised the energy saving process can start again, with the load shared across only those modules required to meet the load kVA/kW demands. To help prolong the working life of the UPS modules, they can be cycled by the control architecture to ensure all modules received a similar amount of time supporting the load.

The process ensure that there is always sufficient power protection for the connected loads whilst ensuring the highest levels of operating energy efficiency and therefore a lower running cost.

Modular Power System Maintenance and Service

With a modular UPS, the typical mean time to repair (MTTR) is around 30 minutes. This is due to the fact the modules can be hot-swapped whilst the UPS system is operational. A monoblock UPS may have an MTTR of around 1-2 hours in comparison depending on which assembly or PCB requires replacement. It is therefore easier to maintain and service a modular system and the service engineer’s time on site can be spent interrogating the operating logs or inspecting the battery set.

A modular system will have a similar mean time between failure (MTBF) to a monoblock transformerless UPS of around 200,000. This is the defined by the static switch arrangement which may be centralised in the UPS module frame or decentralised into each UPS module.

UPS Uptime and Resilience

Modular systems are better able to help a server room or datacentre meet the ‘high availability’ requirements of EN50600-2-2 (class 3) to achieve 99.995% (four nines) availability. This level of availability requires a redundant configuration, which can be more easily achieved with a modular UPS system where one additional UPS modules can provide N+1 redundancy. With a monoblock UPS, another complete uninterruptible power supply must be installed in parallel to the original one to provide N+1 redundancy. This is not only more costly in terms of capital investment but installation and running costs.

Modular UPS Battery Packs

There are two types of battery set arrangements for a modular UPS system. The first is a traditional valve-regulated lead acid (VRLA) battery set and the second is a lithium-ion set of batteries. Lead acid battery technology has been the standard type used in uninterruptible power supply installations. The batteries are available with 5-year and 10-year design lives with replacement typically taking place within years 3-4 and 7-8 respectively. Lead acid battery technology is particularly suited to standby power applications including modular UPS. A typical lead acid battery set will recharge to 80% within 24hours.

Lithium-ion or Li-ion batteries have a longer design life of 10-15 years are becoming a popular alternative to lead acid. Though a lithium battery set will have a 20% plus price premium over lead acid, the price has to be off-set over the working life of the battery and the ability of lithium-ion to support more frequent charge/discharge cycles. A lithium-ion battery can recharge to 80% capacity within 2-3 hours. Lithium-ion batteries.

For data centre applications in particular, lithium-ion batteries can provide several benefits in addition to faster recharge times. Compared to lead acid UPS batteries, lithium batteries re around 30% more compact, leading to a small footprint for a comparable modular UPS and battery set.

Lithium batteries are also more heat tolerant. A lead acid battery has to have an ambient environment of 20-25⁰C. For every 1degree rise above 30⁰C the design life halves. Lithium batteries are tolerant and can withstand higher ambient temperatures (as can the electronics used within a modular UPS) leading to lower cooling loads.

Most modern modular UPS systems incorporate firmware settings for their charging assemblies to accommodate lead acid and lithium batteries. The configuration may also be a factory build option.

Modular UPS battery sets can consist of either battery technology and be installed as plug-in battery cartridges or in external battery cabinets or cladded or open battery stands. The physical installation options available are brand and UPS range specific.

For more information on our modular UPS systems please contact our projects team.