Maintenance Checklists For UPS Systems

There are thousands of uninterruptible power supplies in the UK run without a UPS maintenance contract. They tend to be protecting smaller installations and are almost always run on a ‘fix when it breaks’ policy. Is this the best way to manage a critical power system?

The answer is of course no because an uninterruptible power supply is a device that you need to work when you need it most. It’s a bit like the landing gear on an airplane, you can guarantee a safe landing if it fails and could lose the entire system.

The same is true of a UPS system. When the mans power fails, the UPS should be capable of supporting the load, using its battery set to power the inverter section and keep your systems running. The runtime period should be long enough for a safe system shutdown or to ride through the power cut.

Battery failures account for over 80% of all UPS failures. The majority of battery failures occur when the battery set is put under load i.e. during a mains power failure and when you really do need a health UPS battery set. During normal running a UPS system could alarm to indicate a potential battery fault.

During a UPS preventative maintenance visit, battery inspection is just one of several inspections that are carried out. Others include an inspection of the UPS system itself, connected mains cables, battery cables, distribution boards and the external maintenance bypass switch, if installed. Where necessary terminal and battery connections can be tightened and re-torqued. Alarm and system logs are also inspected to see how the uninterruptible power supply has performed since installed and/or the previous service visits.

The UPS system and other internal components are also visually inspected for cleanliness and signs of ageing. Components can include cooling fans, AC and DC electrolytic capacitors, circuit boards and wiring. All of these can show signs of ageing including heat damage and corrosion from exposure to corrosive dusts, chemical environments and even salt air.

Aside from visual inspections during a preventative UPS maintenance visit thermal imaging and electrical testing should also be performed. Thermal imaging can help to identify heat spots within a unit and connected LV switchgear and especially in hard to access areas.

Electrical measurements can be taken to measure input and output performance characteristics and load banks can be used to apply dummy loads. Load bank testing allows a UPS system to be tested without interruption to the critical power load which may be run on a bypass supply. The load provides not only a test of the UPS system but the ability of the connected battery set to support the load and at step changes in load profile: 25, 50, 75 and 100% load and the runtime performance recorded.

Individual batteries can also be tested using a hand-held battery tester and their measurements recorded. Over time this can give a good picture as to the overall battery system and individual battery block health, identifying individual batteries that could lead to a potential battery set failure.

During each inspection visit, the UPS maintenance engineer should follow a set UPS service procedure and maintain records and logs. These should be kept in a local file and be easily accessible on request by the UPS service engineer. Electronic copies should also be kept for remote access and security.

Over time UPS maintenance logs can provide a good overview of the operational history, identifying problems, PCB, component and battery changes and any overall concerns for the site staff to address.

Preventative maintenance visit are vital to the overall health of a UPS system no matter what its application and size. Without maintenance, an uninterruptible power supply cannot provide a guaranteed source of critical power and could fail just when it is needed most, when a power failure occurs.

The Eco Power projects team provides UPS maintenance on a wide range of uninterruptible power supplies across the UK. For a free assessment call the team on 0800 612 7388.