In order to maintain losses and cooling efforts of growing capacity and power rating of battery energy storage systems the battery system voltage will have to be increased significantly. Hence novel high voltage battery energy storage systems (HV-BESS) are the subject of development in various cases with high power demands in mobile and static applications. In contrast to low voltage battery energy storage systems (LV-BESS), a special characteristic of these high voltage systems is the large amount of battery cells connected in series and the tendency to fewer parallel strings. The use of high-power high-voltage battery systems must not decrease the reliability of the HV-BESS, therefore a continued operation after a single fault is essential. This requirement leads to the necessity of re-evaluating faults in a HV-BESS. Preliminary investigations are indicating that high differential static and transient voltages may occur at open-circuit faults and switches which can be summarized in three major categories: 1. Controlled / planned switching (controllable timing and defined rise and fall parameters), 2. Faulty contacts or connections (sudden open-circuit situation in one string), 3. Internal or external short circuits (consequences of triggered active and passive protection devices in the system).
In this article, relevant possibilities of failures in a HV-BESS and the mandatory following active switching actions and passive system responses are evaluated. The spatial and topological position of switches, regarding to the source and location of possible faults, the protection against the individual static and transient electrical stress is discussed and differences between LV- and HV-BESS are presented.