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Power System Reliability Analysis

Reliability Analysis

Arc Flash Advisors perform Reliability studies to maximize the reliability, efficiency, and safety of an electric power system. Depending on your particular needs, protective-device coordination, short-circuit, and load-flow studies may be performed and incorporated with the reliability study.

When comparing various industrial power system design alternatives, acceptable system performance quality factors (including reliability) and cost are essential in selecting an optimum design. A reliability index is the probability that a device will function without failure over a specified time period. This probability is determined by equipment maintenance requirements and failure rates. Using probability and statistical analyses, the reliability of a power system can be studied in depth with digital computer programs.

Reliability is most often expressed as the frequency of interruptions and expected number of hours of interruptions during one year of system operation. Momentary and sustained system interruptions, component failures, and outage rates are used in some reliability programs to compute overall system reliability indexes at any node in the system, and to investigate sensitivity of these indexes to parameter changes. With these results, economics and reliability can be considered to select the optimum power system design.

In many cases, a reliability study will include a site visit by a field engineer to assess factors such as:


  • Location and placement of surge arresters
  • Protection and coordination design guidelines
  • Equipment operation and maintenance practices
  • Outage response procedures
  • Outage reporting databases
  • Primary-fuse sizing practices for pole-top and pad-mounted transformers
  • Transformer sizing and loading data
  • Equipment failure and reliability data
  • Equipment installation and commissioning procedures
  • Construction standards for new and existing equipment
  • Outage restoration and sectionalizing procedures
  • Distribution automation practices and equipment performance data
  • Tree trimming practices
  • Other specified practices, procedures, and guidelines

Following the site visit, a comprehensive report is submitted discussing the findings and suggesting ways to improve overall reliability of the distribution system. The economics of preventive maintenance and continued operation of older equipment are considered, including downtime, repair costs, and production losses. Recommendations may include replacement of marginal equipment and/or equipment approaching the end of its service life.