Firstly – expandability. Let us suppose you are developing a data room. The plan is to eventually have, for example, 25 cabinets, each with a power consumption of 3KVA = 75KVA total load. However, at present you only need power for 5 (15KVA), with the remainder being added over the next few years or so.

The sensible approach using the standard Uninterruptible Power Supply would be to fit an 80KVA model. However in the early days it would only be operating at less than 20% capacity. So you’ve shelled out for an 80KVA system that wont be at capacity for a couple of years. For an 80KVA system (excluding battery and installation) you’d be looking at a cost in the region of £8,000, depending on options.

With the Modular UPS, you would fit a 100KVA carrier, and 2x10KVA Power Modules at a cost of around £6,000. You can then add the additional 10KVA power modules as and when required at around £1,500 each.

The benefit here is that the initial outlay is lower, however the total cost will be higher, as you need to add in another 6x 10KVA Power Modules units, making the total cost £15,000 as opposed to £8,000 for the standard Uninterruptible Power Supply.

However, let us now suppose that we want a n+1 redundant solution. So with our standard Uninterruptible Power Supply model, we would put in 2x80KVA UPS Systems, at an upfront cost of £16,000. With the Modular UPS we can put in the 1 extra power module that we need, so our initial upfront cost is 1x 100KVA carrier, and 3x 10KVA Power Modules at a cost of around £7,500.

However, the real benefit is to do with the fact that to achieve n+1 we only need 90KVA of UPS power, as opposed to 160KVA in the configuration above. When the data centre is fully operational we would require 1x 100KVA carrier, and 9x 10KVA Power Modules at a cost of around £16,500. So, slightly more expensive but in an equivalent ball park, however other important factors are that the Modular UPS is in one cabinet with a small footprint, occupying probably half the space of the 2x 80KVA Standard UPS Systems and the fact that the power modules can be easily swapped in the event of a fault – thereby improving on availability figures.

It would be remiss of me however, not to include a third scenario. N+1 Redundancy is achieved by having one more Uninterruptible Power Supply than is needed to do the job. Therefore, it is possible to use, for example 3x40KVA UPS Systems, or 4x30KVA UPS Systems, that too, can grow with demand. If we take the latter, we would need initially 2x30KVA UPS Systems at a £6,000 outlay. You can add another for another £3,000, and then finally have the last in, at a total cost of £12,000. Of course, this price excludes batteries and installation. However, in this instance you need to have room for 4 UPS Systems!

I have also not included the additional costs of switch gear needed for the standard Uninterruptible Power Supply Solution. So, taking this into account, along with the additional floor space needed, you would have to argue that the Modular UPS would be a good solution.

There is another factor that gives the Modular UPS a wholesale advantage over other methods and that is efficiency. Let us assume for a moment, that the Modular UPS and the Standard Uninterruptible Power Supply, all share the same efficiency at full load. It is clear that UPS systems operating at half load or less will be less efficient. With 2x80KVA UPS Systems on a 75KVA load, each UPS will be operating at 47% load, whereas the Modular UPS with 90KVA of power available, will be operating at 83% load. So there is probably some running cost calculation that you could also take into account.

Money makes the world go round as they say, so if I were looking for simple UPS support, I’d opt for the standard Uninterrupibtle Power Supply, however if I was needing to include some redundancy in there, the Modular UPS is starting to look like a great contender.

Now UPS Systems are designed to increase the reliability of connected systems, by providing power protection and back up power. If the UPS System should fail then it should revert to bypass and allow utility mains power through (this is for online double conversion Uninterruptible Power Supplies and particularly three phase systems). It’s unclear what happened in this case, but whatever the outcome the critical systems were left without power and the UPS System is perceived not to have done its job.

Here’s where redundancy is required. Basically, you have one more system than you actually need, therefore if one system should fail, the other can take over without any loss of UPS System support. Should the utility fail for an extended period, then you either need batteries to keep you going (or shut down gracefully) or an external generator to kick in and simulate utility power.

Redundancy is usually expressed as ‘n+1′, which means that if you need ‘n’ UPS Systems to power your load, then you install ‘n+1′. For example, if you have a 100KVA load, you can achieve this with 1x100KVA UPS System. If you want redundancy you will need to use n+1 = 1+1 =2 UPS Systems, i.e. 2x 100KVA UPS Systems. Alternatively, you may have achieved your load by using 2x50KVA UPS Systems in parallel, and redundancy can be achieved by installing an additional 50KVA UPS System i.e. 3x50KVA UPS Systems, which may be more cost effective.

I’ll blog more about this later, as the citizens of Taipei walk to work. 

You can read about the Taipei metro power cut here