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Backup Power: "Back" To The Basics

Mon, 03/24/2008 - 11:42am
Bill Brown, P.E., Lead Engineer, Critical Power Consulting, Square D & Critical Power Competency Center/Schneider Electric

Optimizing a backup power solution for your facility’s specific needs can improve reliability without breaking the bank

 

Backup power solutions range from simple to complex, and from relatively inexpensive to major capital expenditure opportunities

Backup power solutions range from simple to complex, and from relatively inexpensive to major capital expenditure opportunities.

In today’s business climate, reliability requirements force the consideration of backup power when power from the electric utility is unavailable. But what type of backup power should you be considering? With the number of available solutions on the market today, the issue of just what solution fits a particular facility’s needs should be considered before making such a crucial and potentially costly investment.

Knowing Your Needs

The most fundamental question to be considered here is, “What level of electric power reliability is required?” The answer is highly dependent upon the process needs of the facility. One assembly process, for example, may be able to tolerate short-duration outages, while at the other end of the spectrum, such an outage could cause critical damage to tooling for a semiconductor fabrication process.

In between, there is an entire range of sensitivities to short-term outages of different durations, as well as to extended loss of power.

The very term “outage” may have different meanings to different people. From an engineering standpoint, more definition is required to fully capture the types of phenomena against which a backup power system is to protect. Such definition is where “backup power” and “power quality” may overlap.

The effects of voltage sags, swells, and transients must be considered, and each situation is unique. In addition, being able to quantify the frequency of occurrence and nature of electric power “incidents” using an electronic multi-function metering platform is crucial to obtaining a full understanding of the utility power supply performance over time.

Needs To Solutions

Backup power solutions range from simple to complex, and from relatively inexpensive to major capital expenditure opportunities. Take, for example, a facility with processes that can tolerate short-term outages of a few seconds, but not sustained outages. One solution for such a facility, barring any code or other regulatory requirements, could be a second utility service, supplied from a different substation, with a system to automatically transfer between the two. Or, backup generation might be used, along with a system to automatically transfer to the backup generation, should a utility outage occur.

Contrast this with a facility that cannot tolerate even a momentary interruption of power, in which case uninterruptible power supplies may need to be employed, along with backup generation.

Another example might be a facility with processes that can tolerate brief utility service outages, but not voltage sags. Such a facility may be best served by installing compensating devices such as dynamic voltage restorers, which are typically not categorized as “backup power” devices but rather as “power quality” devices.

Design, Install, Commission

Inevitably, implementation of a backup power solution, whether for a new facility or a facility that has been in operation for some period of time, requires utilizing the services of a design professional. Such professionals can help quantify a facility’s backup power needs and match the optimum solution to it. They can also, as part of the design process, further refine such a solution. For example, suppose backup generation is being considered for a facility. You may want to ask the following questions:

  • How many generators are required?
  • Should they be powered by diesel fuel, natural gas, or steam?
  • Are there emissions requirements that must be taken into account?
  • What is the optimum generator design for the given process loads?
  • What about paralleling switchgear?
  • What protective devices are required, and what should their settings be?
  • Is there a chance that co-generation is a possibility?
  • What about arc-flash hazards?
  • What type of metering is required, and where?

The answers to these questions, and many more, affect the ultimate choice of equipment, how it is housed, and in what ways it can be used. This can be especially challenging due to the fact that most backup power equipment is, by its nature, complex.

Once equipment has been specified and purchased, manufacturing quality and proper installation are critical. Proper commissioning is also vital. In most cases, commissioning differs from simple startup of equipment, because it tests whole systems and across systems under real-world conditions. Any deficiencies must be corrected before the system can be relied upon to meet the facility’s backup power needs.

Make It Maintainable

With any backup power system, it is essential that the proper preventive maintenance be performed, and that the system lend itself to being maintained. Such features as drawout circuit breakers, for example, can add immensely to the maintainability of the system. Maintenance concerns are best addressed if they are brought to the forefront during the concept and design phases of a project, not at the end after the system has been commissioned.

Safety Is Paramount

As with any power system, safety is vital to backup power systems. Safety should start with the system design. Engineering controls, such as interlocks to prevent undesirable or unintended operations, can have a huge impact. An enforced safety policy that takes into account shock and arc-flash hazards per NFPA 70E is essential. And, of course, there is no substitute for acute safety awareness by the electrical workers themselves. With these factors taken into consideration, personnel safety and reliable backup power need not be mutually exclusive.

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