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 power systems 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.
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 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.
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 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.
With a modular uninterruptible power system, 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.
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.
For more information on our modular UPS systems please contact our projects team.