The entire point of any UPS installation is to provide guaranteed power availability to its supported load; to fulfil this requirement, the UPS itself must be correctly maintained. Alan Luscombe, Marketing Director at Uninterruptible Power Supplies Ltd, a Kohler company, looks at the essential elements of effective UPS maintenance.
As a UPS’s role is to support other items of electronic and electrical equipment – often in large numbers and in critical applications – the importance of keeping the UPS itself fully functional and available online becomes paramount. This availability depends heavily on having a professional maintenance programme that covers regular preventative servicing and emergency call-out facilities for all the components of the UPS installation. A number of steps comprise the ongoing coverage essential for assured UPS power availability.
1. How do I start?
Ensure the UPS is kept in optimum condition within a clean, dry, tidy and well-lit area, while all alarms and indications are recorded, logged and reported correctly. A named member of staff should have responsibility for the UPS and its associated equipment, and a suitable maintenance contract negotiated with a reputable UPS specialist.
2. What should the maintenance contract include?
A regular testing and preventative maintenance schedule; emergency call-out facilities with a guaranteed response time; and a policy for end-of-life component replacement.
3. What is the scope of the maintenance schedule?
The schedule should cover all the UPS installation’s major parts; the UPS itself, the battery and the generator if present. The schedule will be based on a planned programme of visits in which service technicians perform inspection and maintenance as required.
4. How should the UPS itself be serviced?
All UPS meters and instrumentation should be checked for correct operation, and any meter readings checked, recorded and verified for accuracy. Local and remote monitoring panels and communications channels, as well as indicator lamps, should be checked for correct status indication. Switchgear and circuit breaker operation should also be proved.
Environmental conditions should then be reviewed, and all obstructions removed from around the equipment. Ensure that airflow in and around the installation is unimpeded, while changing any air filters that are due for replacement.
The equipment itself should be checked for excessive heat, noise or vibration, and signs of damage to components or to power and control wiring and connections. This includes looking for swelling and leakage on ac and dc capacitors. Check power supply voltages and waveforms, together with the overall UPS operation.
The service plan should also identify the degradation of any critical components, allowing repairs or replacement to be performed before a fault occurs. Backup spares should be available immediately on demand.
5. Battery maintenance techniques
For today’s VRLA batteries, battery impedance testing provides an essential maintenance tool. This approach depends on age-related changes in battery impedance. The internal impedance of a new battery is low, and measured in milliohms. As the battery ages its impedance increases marginally due to normal internal corrosion. For healthy batteries, this rate of increase should be uniform across the single and parallel arrays of serial battery strings that comprise them. Any battery, or group of batteries that shows an impedance increase higher than the others becomes suspect.
Battery impedance testing is easy to perform, and almost all battery problems manifest themselves as a rise in internal impedance. These include electrolyte loss due to venting through overcharging, leakage through seals, or sometimes migration of electrolyte between cells. Occasionally, excessive corrosion can cause loss of metal area or even disintegration within a battery. To test, pass an AC current at a level related to the battery Ah rating through the battery; then use this value and the millivolt reading across the battery terminals to calculate the internal impedance.
Regular impedance testing will track battery condition and allow accurate prediction of the end of the battery’s reliable working life. Fig.1, recorded near the end of a battery’s life, shows how impedance readings provide a better indication of problems than float voltage readings do. Impedance readings for blocks 8 and 9 are high, revealing problems not made visible by voltage readings.
Fig.1: Impedance graph for battery at end of its working life
6. Generator and overall system checking
Generators, frequently part of a site’s power protection, should also have a regular service program. This should cover all major generator components, including the cooling, fuel and lubrication systems, the starting system and mechanical parts, and control panel. Insulation and load testing should also be performed.
As well as planned maintenance of the UPS, battery and generator components, occasional testing of the entire system is also worth considering. This test could ensure that the automatic mains failure (AMF) equipment functions correctly, the generator starts properly, the UPS accepts output from the generator successfully and the batteries recharge normally.
7. Emergency call-out resource
Even good-quality, well maintained equipment can fail occasionally, so any scheduled maintenance plan must be complemented by an emergency call-out service. Different options should exist, allowing UPS users to balance response levels against cost. Telephone support is typically 24/7/365, while a guaranteed time within which a service engineer arrives on site following a call-out is negotiable. Similarly, levels of spareholding can be discussed and negotiated.
As mentioned, UPSs exist solely to provide uninterrupted power availability to their protected loads. This protection level is achievable by purchasing well-specified UPS equipment from reputable suppliers, and combining the steps above into a maintenance programme appropriate to the needs of the equipment and its supported load.