KS-20472 Round Cell Issue

1. Evaluation of Battery Technologies to Replace KS-20472 Round CellsJohn Bailey, Quad Cities Senior Staff Engineer Objective: Present issue background information and opportunities for using alternate battery technologies.

2. KS-20472 Round Cell Issue • Summary of Issue: The KS-20472 cells used by many plants have become obsolete and replacement cells of this type are generally not available. An Exelon plant has begun to experience multiple cracks of these on cell lids and jars. The KS-20472 Round Cells are used as a 250VDC emergency power source for the Emergency Bearing Oil Pump. The cracking has resulted in; electrolyte spills, minor battery fires, and emergent battery cell replacements. • Failed Cells SN078 and SN119 were sent to for failure analysis. • Failure analysis concluded the cause of failure was “attributed to external mechanical loading of the positive terminals.” No attempt was made to identify the source of the loading, but it is the consensus of the affected plant’s system managers that the most likely cause of the loading is the result of externally induced stresses associated with construction.

3. KS-20472 Round Cell Issue KS-20472 Round Cell Construction and Installation

4. KS-20472 Round Cell Issue Specifics from failure analysis report EXE-32991. • Battery SN078 • The plastic lid cracks originated at the positive terminal. The plastic crack pattern was consistent with excessive movement of the positive terminal away from the center terminal. This force also resulted in a permanent deflection of the positive terminal post. The lid crack extended into the jar, which would allow fluid to leak from the battery. • The as-received condition of battery SN078 is shown in Figure 3. The battery had two large cracks that appear to originate around two corners of the positive terminal and then propagated into the jar body. The crack extended several inches into the jar. • The acid was neutralized and the battery was discharged. The jar was sectioned to evaluate the terminal posts and the internal components. The terminal posts were clean and free of corrosion products. The positive terminal was bent to an angle of approximately 11degrees off vertical as shown in Figure 4.

5. KS-20472 Round Cell Issue

6. KS-20472 Round Cell Issue

7. KS-20472 Round Cell Issue • Battery SN119 • The plastic lid cracks originated at the positive terminal post. The plastic crack pattern was consistent with movement of the positive terminal post toward and/or away from the center terminal. The internal joints connecting the positive terminal post to the battery cells were also broken on both sides. There was a dark discoloration of the plastic on one side of the battery which was likely due to hydrogen generation at the broken joint location, while the battery was in service. The lid crack extended into the jar, which would allow fluid to leak from the battery. • The acid was neutralized, the battery discharged and sectioned to evaluate the internal components. The internal joints connecting the positive terminal post to the battery cells were both broken, Figure 6. This allowed the positive terminal post to be easily moved. The terminal posts were clean and free of corrosion products

8. KS-20472 Round Cell Issue

9. KS-20472 Round Cell Issue

10. KS-20472 Round Cell Issue Corrective actions (in progress): • Replace the KS-20472 round cells with a “standard design” lead calcium battery cell similar to the type used in most stationary battery designs. Advantage 1. Known technology, readily available, small procurement lead times. 2. Provides a rapid solution to the ongoing failure mechanism documented in the failure analysis report.

11. KS-20472 Round Cell Issue Disadvantages: • KS-20472 Round Cells were specifically designed for long service life (40 years) in a high temperature environment. The round shape provides better geometry to accommodate positive plate growth and a pure lead grid is provided to lower grid corrosion rates. Conventional rectangular cells typically use a grids constructed of Lead/Calcium plates. This cell design has functional advantages, but they are not tolerant of continuous high heat loads. (approximately 90F) • It is expected that the effective service life of Lead Calcium cells used in this application will have a service life of 8-10 years.

12. KS-20472 Round Cell Issue Battery Technology Review: Two alternative technologies were identified: • Nickel-Cadmium (Ni-Cad) flooded cells. • Lead Selenium (Pb-Se/Low Antimony) flooded cells. Ni-Cad cell technology is well understood but was removed from consideration primarily due to its lower operating voltage of 1.2 VPC. The use of a Ni-Cad cell in the Quad application would have required additional floor space to accommodate the greater number of cells needed to meet the 250VDC application requirement.

13. KS-20472 Round Cell Issue Pb-Se Technology appears to be a good solution for a battery located in a high temperature environment. • Due to the use of lead, the open cell voltage of a Pb-Se cell is compatible with the existing Pb-Ca technology so replacement of the system chargers is not required. • The use of tubular positive plates instead of a rectangular grid provides higher power density due to increased surface area. • Tubular positive plates removes the need for horizontal support bars. The lack of the horizontal support virtually eliminate positive post growth which is accelerated by high temperatures.

14. KS-20472 Round Cell Issue Discussion: • What is utility experience with Pb-Se batteries. • Are there other battery technologies that should be considered for this application?

15. Questions? IEEE 6/14/2016 KS-20472 Round Cell Issue John Bailey