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Learning the Reliability Lingo

Oct 1, 2004 12:00 PM, By Michael Eby, Editor-in-Chief

Probability of failure. Availability. Mean time to repair. Failure rate. Unavailability. Failure mode. Mean time to failure. Interruption. Dirty power. Do these terms and phrases mean anything to you?

Probability of failure. Availability. Mean time to repair. Failure rate. Unavailability. Failure mode. Mean time to failure. Interruption. Dirty power. Momentary outage. Transient. SAIDI. SAIFI.

Do these terms and phrases mean anything to you? If you're responsible for keeping the power flowing in your facility, I should hope so. Unfortunately, it seems like more than a few people out there misunderstand these terms or the general concepts of reliability and how best to assess a facility and make recommendations for improvement.

Many people today try to wrap reliability of power delivery into a nice little package by focusing on the power of nines. This concept looks at the relationship between downtime and availability of power and presents the answer as the “number of nines.” For example, you or your customer may want six nines of availability on your system, which equates to a mere 32 seconds of downtime per year.

But do you know how much it would cost to design and build a system to deliver this level of reliability? Sure, you can create a system with N+2 design, but can you afford to build it? Or better yet, do you really even need a system with this much reliability built in?

But system design is only one factor in the reliability equation. Operations and maintenance issues can be just as critical as the initial system design. In fact, as Wally Vahlstrom points out in “A Practical Guide for Electric Reliability” on page 48, it has been estimated that 70% to 80% of all unplanned shutdowns are due to human error. This is where you can contribute the most to the reliability of your facility's electrical system. Being prepared for and quickly dealing with an interruption in power is critical to your success or failure on the reliability front.

Maintain up-to-date records and keep a spare parts inventory for every piece of critical equipment on the system. Implement a detailed maintenance program and make sure everyone follows the schedules. Create a comprehensive safety program and maintain current records for those in need of training. Monitor load levels throughout the facility and make sure short-circuit and coordination studies are revised whenever equipment is added to the system or loads are rearranged.

These are just a few of the things you can do to improve the reliability levels at your facility. For additional guidance on this topic check out the electrical maintenance and operation process checklist in the cover story on page 52. Or better yet, make plans to attend the Power Quality Exhibition and Conference in Chicago from Nov. 14-18 and learn some new tricks from the industry experts.

You might even learn a few new words to add to your power quality vocab.

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© 2012 Penton Business Media, Inc.

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