By Jim Moon, Serveron Corporation
May 28, 2002 — Utilities are under intense pressure to keep equipment running flawlessly, leading to a strong demand for monitoring technologies to enhance reliability.
In contrast to high-visibility assets such as major transformers, it is sometimes easy to overlook the uninterruptible power supply (UPS) batteries that are called upon only when other equipment fails.
The consequences of a battery system failure can include equipment damage and extended or more widespread outages.
The new battery and cell management system by Serveron Corporation monitors the battery bank as a unit as well as the cells individually. Developed in conjunction with EPRI, Serveron’s system consists of a bank manager unit for the battery bank and individual cell monitors for each cell in the bank. The bank manager provides key bank measurements, overall control and communication to each cell monitor, and communication to a host site for uploading data and reporting. The daisy-chained cell monitors provide key cell measurements and the critical ability to bypass overcharging cells, which protects against the detrimental effects of traditional battery management practices.
Traditionally, all cells are charged to a minimum level with float current. However, float current applied to the bank as a whole degrades fully charged cells (overcharging the strongest cells causes electrolysis, with the consequent loss of electrolyte even with valve-regulated cells). In addition, force equalization to bring weaker cells up to the level of stronger cells undermines the strongest cells even more aggressively than float.
The Serveron system eliminates this electrolysis with a current path that bypasses any fully charged cell. As a result, float current charges only the weakest cells to bring them up to the nominal charge voltage. By bypassing float current around stronger cells, the life of individual cells and therefore the battery bank as a whole is extended and overall substation reliability is improved.
Serveron’s monitors measure all the key physical and electrical parameters to characterize the condition of the bank and the cells. These measurements are made both at float and under short-duration discharge. The latter measurements enable the Serveron system to find cell and current-path defects that are not detectable during float charging. Applying a discharge load for 1 msec allows the system to measure internal plate-to-post resistance and external strap-to-post resistance.
By this method, Serveron’s monitors can find bank defects that would only become evident during discharge. Using Serveron’s system, maintenance personnel can inspect and track cell status remotely via a secure web site, making maintenance calls only when problems are detected.
A Serveron battery management system is installed at the Grand Coulee Dam in Washington State, where the system identified an internal failure in a specific cell and in the charger, which engineers were able to correct.
“Serveron’s technology has helped keep the battery bank at peak performance level. When there was a fire in the Station Service switch gear, the battery performed properly, avoiding an even worse catastrophe,” said Ray Spackman, the engineer responsible for the batteries. “We expect a useful life for the bank and cells in excess of 40 years.”
More information on Serveron’s battery management system is available at www.serveron.com.