2120 3%4 S Bristol St WCC02 - Plan

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2.1.4 Overview of BMS Operation In battery energy storage systems,one of the most important hazard barriers helping to ensure safety is the battery management system (BMS).The BMS provides primary thermal runaway protection by ensuring that the battery system operates within a safe range of parameters such as its state of charge and temperature. In a UL 9540 listed battery energy storage system,the BMS monitors,controls and optimizes the performance of battery modules and disconnects them from the system in the event of abnormal conditions.The BMS also provides charge and discharge management of the batteries. In case of undervoltage or overvoltage,over-temperature,or overcurrent conditions,the BMS will alarm and then limit the charge and discharge current or power. Under emergency conditions,the BMS will cease operations and electrically disconnect the battery. 2.1.4.1 Hazard Event 1:Thermal Runaway Thermal runaway is defined as the condition when an electrochemical cell increases its temperature through self-heating in an uncontrollable fashion and progresses when the cell’s heat generation is at a higher rate than it can dissipate,potentially leading to off- gassing,fire,or explosion.The cause of a thermal runaway event can range from a manufacturer defect in the cell,external impact,exposure to extreme temperatures,or controls and electrical failures.Furthermore,a thermal runaway event in a single cell can propagate to nearby cells through heat transfer,thus creating a cascading runaway event across battery modules,leading to more heat generation,fire,off gassing,and increased potential for a deflagration event. The Battery 6618 battery module of the Enclosure B160 construction limits cascading thermal runaway events to only several cells as demonstrated by UL 9540A testing.In testing,thermal runaway did not propagate beyond the initiating module. Should thermal runaway occur within a cell or several cells within battery module,a number of key barriers are provided to mitigate against propagation of failure throughout the system leading to more severe consequences. Confidentiality Class External Confidentiality Label Document Type Page Ericsson Internal Analysis 13 (27) Prepared By (Subject Responsible)Approved By (Document Responsible)Checked ERATLEN Thomas Lennholm Document Number Revision Date Reference 1785-BFM 107 220/1 Uen PA2 2025-06-03