Beyond Mission Critical to Hypercritical

摘要

It was once thought that electrical reliability had reached its peak at "six nines." And for many facilities, it is still the standard. As a measure of electrical system availability, six nines means that the power supply is available 99.9999% of the time (see "Average System Availability Index below). This level of power reliability often came at the substantial cost of an uninterruptible power supply (UPS), as well as a backup generator. At today's modern plant, however, six nines falls woefully short of the need. In fact, many plant maintenance and operations professionals acknowledge that when it comes to reliability, there just aren't enough nines. They want 100% reliability. In the real world, perfect reliability may be fiction, but properly evaluated, the appropriate level of reliability can be justified and applied based on hard analysis and prudent application of currently available hardware. The key to the evaluation is knowledge of the elements that control reliability and of the actual costs of outages. Ironically, reliability seems to be on the decline at a time when the need for reliability has never been greater.