Uninterruptible power supplies (UPSs) have an indispensable role to play in an industrial/engineering environment where the mains power, for whatever reason, might fail. A UPS will keep the business from grinding to a halt – indeed, no one may be any the wiser on the factory floor that anything adverse has happened. All the more reason a UPS should be properly maintained and cared for, in order to maximise its useful working life.
First, though… the basics. A UPS is an electrical apparatus that provides emergency power to a load when the input power source, typically the utility mains, is lost. It differs from an auxiliary or emergency power system, or standby generator, in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries and associated electronic circuitry for low power users, and/or by means of generators and flywheels for high power users. UPS units range in size from units designed to protect a single computer without a video monitor (around 200VA rating) to large units powering entire data centres (>1MVA), buildings (>300kVA), or manufacturing processes.
Back, then, to the need for proper care. As Zoltan Gal, global service sales manager power protection, ABB, points out: “Uninterruptible power supplies keep vital services going, even when the mains power is cut, so upkeep and maintenance are really important. The UPS systems are electrical devices and therefore by nature require a regular maintenance performed by trained and certified service engineers.”
ABB’s general recommendation, in terms of maintenance, is one such service per year, although there are industries, such as telecoms, that require as many as four maintenance services per year. The time span between each service depends on operational circumstances. “Environmental conditions affect the UPS maintenance schedule and, where a UPS is installed in a hot and poorly ventilated environment, the maintenance interval decreases,” says Gal.
The life expectancy of a UPS has a wide range – from 12 up to 20 years, varying by the type of UPS employed, he states. “For example, industrial UPSs tend to have a longer life expectancy. A regular maintenance schedule is vital, as this will prolong the lifetime of equipment. Pluggable UPSs, such as small UPS for office applications, often have a shorter life expectancy, because the product is cheap to replace and maintenance is not generally performed.”
Failure to look after UPSs properly carries a high risk that they will start to deteriorate in use and, in the worst-case scenario, fail in operation. “There are multiple risks when a proper care and maintenance schedule is not performed; early aging of components cannot be detected, unwanted UPS behaviours cannot be identified in due time and calibrations cannot be performed, leading to the UPS taking incorrect decisions because of incorrect measurements.”
He also advises that the maintenance of UPSs, being critical devices, should always be performed by trained experts. He recommends the following to get the best returns:
- A clear goal for the power quality strategy – resolving specific issues that have been identified
- Selecting the correct meters to capture data and events – using state-of-the-art technology for reliable results
- Using the right software to visualise and carry out analysis – selecting an expert solutions provider.
Whatever the actual average lifespan of a UPS might be, what was unwavering was that this was always under ‘recommended’ conditions. Any significant deviation from that was likely to have a deleterious impact on the UPS in question. But what are these recommended conditions and just how much do they affect the lifespan of a UPS battery? Maybe even more importantly, how do you make sure the life of your UPS itself is maximised by adhering to these? Three factors consistently cited were unit placement, temperature and cycling frequency. They are explored in more detail below.
Unit Placement – the UPS should not be placed near open windows or areas that contain high amounts of moisture; and the environment should be free of dust and corrosive fumes. The ventilation openings at the front, side, or rear of the unit must not be blocked, in order to provide proper air circulation and avoid over-heating.
Temperature – most UPSs have a recommended operating temperature, typically from about 0°C to just over 38°C. A general rule to remember is that for approximately every 10°C above the ambient temperature of 25°C, the life of the UPS and its battery will be reduced by 50%.
Cycling – when a power disruption occurs, the UPS will automatically switch to battery power to provide the attached equipment (load) energy. Once utility power has been restored, the UPS battery will automatically recharge the battery to prepare for the next power outage, a process known as the discharge cycle. The more often discharge cycles occur, the quicker your battery will be depleted. “Cycling is a necessary and unavoidable part of UPS operation,” points out Schneider Electric. “However, being aware of cycling frequency will help to notice abnormal/frequent cycling. Many UPS models are also adjustable, allowing the user to regulate the sensitivity to voltage sags and other transients to reduce ‘nuisance trips’ that unnecessarily consume battery capacity.”
One recent development in the area of uninterruptible power supply is the use of hydrogen fuel cells as energy storage or generator. Critical Power Supplies states: “In combination with an electrolyser, which is driven by regenerative energy sources like wind, sun or geothermal power, a hydrogen fuel cell can realise a very economic, self-sufficient and also ecological emergency power supply.” An electrolyser divides the water arising at electricity generation back into its components, oxygen and hydrogen, which then, in turn, can react and release energy. “Such a circulatory system is absolutely network-independent, with low emission, low operating costs and is based on harmless substances, which don’t burden the environment.”
On a more worrying note, HSE has recently carried out several investigations into dangerous occurrences that resulted from a failure of industrial UPS systems at onshore major hazard establishments (see www.is.gd/cidiya). In all cases, it identified that the information for maintenance included in the OEMs’ operating and maintenance instructions did not provide adequate information to allow the continued safe and reliable operation of the industrial UPS systems prior to the incident; for example, implementation of a suitable maintenance regime. These industrial UPS systems were supplied by various manufacturers. The failure of the systems typically resulted in a loss of power to industrial control systems, emergency shutdown systems and emergency mitigation systems. HSE says designers, manufacturers, importers and suppliers should review the information for maintenance (including inspection) provided with the current range of industrial UPS systems to ensure that it satisfies legal requirements.