Battery Reliability: An Advantage of the PureWave UPS™ System.

PureWave UPS High-Power Lead-Acid Battery

The battery system used in the off-line-design PureWave UPS System has proven to be the most reliable energy storage technology of any uninterruptible power supply in use today. The PureWave UPS design team realized that near-flawless battery performance could be achieved by carefully managing the battery environment, operating parameters, and equalization-charging technique.

Development of the PureWave UPS System began 10 years ago. Through collaboration with the Delphi Division of General Motors, it was determined that Delphi’s Delco 1150 battery is very durable and capable of repeated high-current discharges, making it ideal for high-power, short-duty UPS applications. The Delco 1150 uses a unique wrought-plate construction that enhances power-discharge performance and overall reliability. This performance has been demonstrated over many years, with production volume in the tens of millions.

From an analysis of the performance of the first 200 250-kW power modules shipped since 1996, it has been determined that the MTBF for the PureWave battery system is 500,000 hours . . . and growing. This analysis covers over 9,900 individual Delco 1150 batteries and over 2,000,000 hours of operating experience. As of June 30, 2002, only three Delco batteries experienced problems requiring replacement. At no time did the performance of these batteries impact the performance of the PureWave UPS System.

The exceptional track record of the Delco 1150 in PureWave UPS applications is the result of a carefully executed design and a testing program aimed at making sure all aspects of battery performance and life are properly addressed. Its key elements include:

Individual battery testing at the factory.
Performance testing of each 250-kW string of 48 batteries prior to final acceptance.
Stabilized-temperature environment within the air-conditioned energy storage container.
Proper equalization charging utilizing a proprietary algorithm, with an individual temperature-compensated charger for each battery string.
No exposure of the battery strings to dc ripple current.
Constant monitoring of each battery string and its performance during each discharge.
Programmed replacement of each string after 5 years of service life.

Energy Storage Performance Comparison

The graph compares the Mean Time Between Failure (MTBF) performance of the most popular UPS energy storage technologies in use today. In each instance, the value indicated is based on 2,000,000 or more hours of actual field performance . . . not projected calculations.

Energy Storage Performance Comparison graph

Several recently published technical papers and articles discuss the reliability of batteries and flywheels in support of this data.

Wet-Cell Lead-Acid Batteries

Traditional lead-acid wet-cell batteries have been reasonably successful in UPS applications, but take up significant space and require regular maintenance. And they are quite expensive. For UPS applications up to 500 kW, wet-cell batteries can represent 30% to 40% of the total equipment cost. Thin-plate wet-cell batteries in UPS applications have an MTBF of 80,000 hours or less, and generally require replacement within the first 10 years of service.

VRLA Batteries

VRLA batteries are the design of choice for on-line UPS. VRLA batteries can be arranged in smaller cabinets and mounted adjacent to the UPS equipment without special ventilation. “Valve-regulated” means the batteries are sealed and only vent hydrogen if overcharged. VRLA also are smaller in size due to their reduced volume of electrolyte and thinner plates. However, VRLA batteries are exposed to dc ripple current from the UPS rectifier and receive limited equalization charging. Over a short period of time, VRLA batteries begin to experience “weak cells,” resulting in premature failure. Failure of one cell can result in the entire system being unable to provide power to the critical load during a utility source problem. A recent independent study concludes that 66% of VRLA batteries require replacement within 3 to 4 years of service, while a leading VRLA battery supplier now recommends that VRLA batteries should be replaced every 3 years in small UPS systems, and every 4 to 6 years in higher-rated kVA systems.

Flywheel Energy Storage

Flywheel UPSs utilize both mechanical and power-electronic components. A mechanical problem in a flywheel system can result in a loss of protection for the critical load.

According to data published by flywheel suppliers, the new smaller flywheels have achieved an MTBF of 50,000 hours, while older, low rpm flywheels have an MTBF of just over 100,000 hours.

Conclusion

The performance of the PureWave UPS battery system surpasses that of all other energy storage systems used in UPS applications. In addition to providing higher reliability, the PureWave UPS battery system is lower in initial cost and provides a lower life-cycle cost as well. The results show that lead-acid batteries, properly applied, can achieve extremely high reliability in UPS applications.

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