UPS technology has advanced. Mike Elms, Sales and Marketing Director at CENTIEL, explains what to look for when replacing a system, and why new modular systems offer the best power protection
Reliability is often considered to be the key attribute for any UPS solution. However, a system can be reliable over a period of time, but still fail on a particular occasion – with far-reaching consequences. For this reason availability – a system that ideally will not fail – must be the number one priority when purchasing a UPS solution.
Availability can be expressed using the following equation where MTBF equals Mean Time Before Failure and MTTR equals Mean Time To Repair:
Availability = MTBF/(MTBF + MTTR)
Availability is expressed as a percentage and the key number here is MTTR. If MTTR equals zero, then Availability is always 100 per cent, regardless of MTBF.
In recent years modular systems have introduced a significant step-change in the industry because, when properly configured, they are designed to maximise load availability and system efficiency simultaneously. An important advantage is fast replacement and the hot swappable nature of modules. Replacement in less than 10 minutes lowers this critical MTTR figure, thereby driving up the availability percentage.
This gain is achieved because modular systems have a single frame, containing a number (N) of power modules. These run together and share the load equally between them. The advantage of this N+1 configuration is that if one module fails, it becomes isolated. The remaining modules support the load and system availability is preserved. UPS modules are paralleled vertically within a single frame, and frames can be further paralleled horizontally to provide a completely flexible system. There is no single point of failure, contributing to the highest possible level of availability for power protection. The load also remains protected even when an individual module is being replaced.
In the most modern fourth generation UPS systems each module contains all the necessary power elements, including rectifier, inverter, static switch, display and all the control and monitoring circuitry. This is a better design than those which have a separate single static switch assembly and separate control or intelligence modules, once again removing any single point of failure.
The total cost of ownership (TCO) of any replacement UPS should also be considered. As well as the purchase price, the cost of downtime and ongoing cost of maintenance, and the system operating efficiency, all need to be included when calculating TCO.
Modern modular UPS systems have two distinct advantages which contribute to lowering TCO: a flat efficiency curve and Maximum Energy Management functionality. The latest generation Modular UPS systems therefore have online efficiencies of 97 per cent, providing the lowest operating cost to comparable systems.
For example, a legacy transformer based UPS system will waste much more energy than a modern transformerless system. One organisation was recently looking at replacing two standalone 200kVA UPS units running at 82 per cent efficiency. The replacement Modular UPS system with 5 x 50KVA Modules, operating at 96.5 per cent efficiency gave a calculated annual energy saving of over £37,000.
Modular systems also allow organisations to match the UPS system closely to their actual critical load. If this load changes over time, then the Maximum Energy Management function allows redundant Modules to be selected to active-sleep mode.
Modern Modular systems offer all the advantages of high availability, scalability and flexibility to match an organisation’s changing requirements. In addition, they offer the benefits of fast replacement of modules, a small footprint with high power density, and if correctly configured to ensure system right sizing, operating costs that can be kept to a minimum.
However, any UPS that is not maintained properly may ultimately become unreliable and as a result, its availability will be compromised. It is therefore advisable to consider the benefits of a maintenance contract with a trusted supplier.
Originally featured in Network Computing May 2018