What is your definition of a Modular UPS? A question that, surprisingly, has several answers! We have all become acquainted with those lovely ‘buzz’ words that are associated with modular systems, words like: flexibility, availability, scalability, right-sizing, pay-as-you-grow and hot-swap.. etc..etc. However, the term modular itself can mean different things to different people so it is important to check the nature of what is being described as a ‘modular system’ carefully when buying a UPS solution to ensure the essential power of your datacentre is protected at all times.
A single standalone UPS unit that protects a critical load is known as an N system configuration. This is all very well but lacks any resilience in the event that the UPS unit develops a fault or is offline for preventative maintenance. Simply paralleling a second standalone UPS unit of the same rating gives us that resilience and is known as an N+1 configuration. Of course, you can parallel several standalone units together of an individual smaller rating to give the same philosophy, for example if we took this to the extreme we could have 101 x 1kVA UPS units in parallel which would still offer 100kVA N+1 configuration. Obviously this wouldn’t be practical but you get the picture. By using this philosophy it could be described – at the most simple level – as a modular UPS system. However, there does need to be the associated electrical infrastructure –switchgear etc – to be able to add more standalone units.
Another definition of modular is a standalone UPS designed and manufactured in a modular format. The main component parts of rectifier, inverter and static switch are modular. This means if there is a problem with say the rectifier it can be swapped easily. However, if one component does fail the whole UPS functionality goes down with it. It may be a modular system but its level of availability will not be reliable.
A better solution is what we term: a true modular UPS. This is where several individual UPS modules are contained within a frame. All the individual modules are UPS’s in their own right, all containing a rectifier, inverter and static switch and all operating online in parallel with each other. For example five 60kW UPS modules may typically be contained within a single frame offering a resilient configuration of 240kWs N+1. If required, it takes moments (around 30 seconds) to ‘hot-swap’ a module while the rest of the modules continue to protect the critical load. At no point does the system need to be transferred to maintenance bypass and hence on raw mains.
Some other modular systems include the rectifier and inverter within their modules but the static switch is centralised and separate. This offers a potential single point of failure. It may only take a few moments to replace a separate static switch, but, depending on location, getting to the site to replace it may take a maintenance engineer several hours. During that time the system cannot transfer to static bypass. With a true modular system, where the static switch is included in each module, the rest of the modules in the UPS frame continue to protect the load until it can be replaced. This increases the level of availability dramatically.
Naturally, often cost comes into the decision making process when purchasing a UPS. However, the purpose of a UPS system must be to protect essential power with the highest level of availability. There must be no potential single points of failure. Therefore, it is important to check the configuration and the definition of a modular system carefully before purchasing.
At CENTIEL our design team has been working with data centres for many years at the forefront of technological development. We are the trusted advisors to some of the world’s leading institutions in this field. For this reason, we have developed our pioneering 4th generation true modular UPS system CumulusPower which offers offer industry-leading availability of 99.9999999% (nine, nines), with low total cost of ownership (TCO) through its Maximum Efficiency Management (MEM) and low losses of energy.
This article was featured in DCM Magazine December 2018