Battery Reliability: Preventing the 'Whiplash' Effect with Flywheel Technology Increases Battery Life and the Reliability of UPS Systems

摘要

UPS battery failures are the nightmare of facility managers in mission critical applications. Can flywheels mitigate such problems? The experience with flywheels demonstrates that they can. At Pentadyne we believe there are two appropriate applications for a flywheel energy storage system with a UPS. One application is for the VSS to be installed in place of the battery when an external generator or other source can be brought on-line. The VSS provides the energy to support the DC bus and ride through the transition to a generator. The other application is to place the VSS in parallel with the battery and eliminate the 'coup de fouet'. This approach is attractive to users who, for whatever reason, cannot give up their batteries entirely, but want a better battery experience. Some users feel that if the generator does not start they need time to shut down or attempt a manual start. For these rare but possible scenarios, mission critical facilities still depend on the battery to perform when called upon. Therefore ensuring that the battery is always in the highest state of reliability is very desirable. The 'coup de fouet' is a major wear-and-tear factor that depletes a battery, leading to shorter battery life and poor reliability. It occurs each time the battery is discharged whether due to long-term outages or, more frequently, shorter-term voltage sags and utility reclosure operations. By using a VSS to handle discharge activity the battery remains essentially unused. In other words, by staying "off the battery" the stress inflicted by the "coup de fouet" is prevented. Its capacity is preserved and its life will not be depleted. It will remain in a state of higher reliability and therefore higher availability. The combination of a UPS with battery plus a Pentadyne VSS is more reliable than the battery-only system. With a flywheel in parallel, the battery will achieve a much longer life. It is realistic to expect obtaining closer to the full operational design life of the battery. Where UPS systems have two strings of batteries connected in parallel, or a redundant string configuration, a superior approach would be to use the VSS flywheel to replace one of the strings to protect the single string to gain the same reliability improvement as above. Besides the higher reliability benefit there are substantial financial benefits too. Since the flywheel protects the battery, individual cells or the entire battery will not need to be replaced as often; battery and cell replacement costs can be deferred. The VSS is engineered to run for 15 years without major maintenance, owing to its magnetic bearings and internal vacuum pump, so its maintenance costs are dramatically less than compared to maintaining a battery. It is energy efficient, consuming only 120 Watts when idling, and energy consumption costs will be significantly reduced if the VSS replaces a battery. Economically, the VSS is very competitive compared to a battery over a 2-5 year period, and does not carry the same financial liabilities as a battery. To make it even more financially attractive, leasing programs are also available for the VSS. In conclusion, the Pentadyne VSS is both a technically and financially viable solution to battery reliability problems. Ultimately, the Pentadyne VSS provides greater reliability and lower ownership and operational costs for owners of UPS systems.