Eben Owen, UK channel manager for solutions, for Emerson Network explains why UPS protection is an essential safeguard
A CUT TOO FAR?
The general decline in the economy is causing businesses to look very hard at their operating costs. This will apply not only to existing processes and procedures, but also, perhaps more stringently, to the design of new systems. A fresh look may possibly be taken at traditional system components and radical decisions made. Businesses may even contemplate taking a risk. An example of this would be a decision to limit, or even dispense with, power back-up for an infrastructure reliant on electrical equipment. The decision might be based on comparing the cost of providing power back-up with the possible loss caused by a power failure, or on the judgement that power cuts are so unusual that the cost of providing back-up is not justified.
There are, of course, many instances where power back-up is of paramount importance, such as locations where life support or critical business functions rely on electrical equipment. In such instances, decisions will concern the degree and type of back-up cover rather than whether or not it should be provided. However, in less clear cut circumstances, any decision made should have regard to all the circumstances and to all available information.
For several years Ofgem (Office of Gas and Electricity Markets) has published an annual Electricity Distribution Quality of Service Report. The information given in the Reports is based on percentages and averages, and it is made very clear that a wide range of local issues affect the performance of individual DNOs (Distribution Network Operators). The measures of Quality of Service chiefly concern the number and duration of supply interruptions per year. The Report for 2007/2008 showed, across all DNOs, the average number of customer interruptions, or power cuts, during the year was approximately 70 per 100 customers and that the average minutes lost throughout the year was approximately 65 minutes per customer.
The Report also points out there were a number of short interruptions, being planned power cuts lasting less than three minutes that are brought about by operations of the DNOs, designed to reduce the length of interruptions, the majority being associated with automatic restoration schemes. The average number of short interruptions per 100 connected customers was 86.
In addition to these broad indicators that random interruptions in service apply in every DNO, at an historically fairly consistent level, the Report also shows the average duration of those interruptions. It appears that almost 60% of interruptions in 2007/08 were restored within one hour, whilst some 25% of inerruptions lasted between one and two hours.
It is against this background decisions regarding power back-up must be made. Power failures will happen, which in some 80% of cases have the potential of lasting for between three minutes and two hours. An interruption can, of course, happen at any time on any day and could quite easily occur when the electrical equipment is, in any event, switched off. However, unless the random interruption of power to electrical equipment that is actually in operation is of no consequence, the risk associated with any power interruption must be carefully assessed.The type and extent of the appropriate back-up will be determined by the level of sophistication and the practical function of the equipment itself. One possibility is full continuous activity is required for a specific limited number of hours each day, with the balance being a period at a lower level, perhaps over night. Another location may best be served by a back-up facility that enables ordered equipment and system shut down in the event of power disruption, whilst another, as a business-critical undertaking, will require a facility that provides ongoing, continuous operation until utility power is restored.
Although the Ofgem Report presents the overall average picture of the potential risk of complete power failure, any decision regarding power back-up will also need to take into account the unquantifiable number of occasions when the power supply will be distorted by potentially harmful sags, spikes and other irregularities.
A PROVEN SOLUTION
UPS is one well known protection for electrical equipment against aberrations in the utility power supply. Different UPS topologies provide a range of options, from basic battery back-up as an energy substitute during periods of power irregularity through to sophisticated power conditioning functionality that constantly replaces utility power. Depending on the level of availability required, the UPS solution could be a parallel redundant system, a hot standby system or a dual bus system.
Identifying the actual risk to both electrical equipment and systems of irregularities or failures in the power supply and sizing the appropriate solution is not simple. For this reason leading manufacturers and equipment providers in the industry supply extensive product information. This is most commonly available as printed literature and on providers' websites, complemented in some instances by one-to-one on call technical advice.
THE RIGHT ANSWER
The great majority of businesses, however small or large and wherever situated, as well as many individuals, are likely to be reliant on electricity to power their activities. That fully guaranteed utility power cannot be provided, in terms of both availability and quality, is an established fact. Consequently, UPS back-up solutions will be an important consideration when systems and processes that rely on electrical equipment are being designed. Companies like Emerson Network Power provide a wide range of information and advice to enable the right type and degree of UPS cover to be identified and selected for every type of location.