In order to take advantage of the inherent benefits of an ungrounded system (such as high availability and improved fire protection), it must be planned into the original system design. This planning decision is simplified by the fact that a transformer can be used in industrial Battery Energy Storage Systems due to a higher output (e.g. 500 kW) or when connected to a higher voltage level, thus isolating the BESS galvanically from the main distribution. In addition, the DC circuit between the battery and the inverter is usually designed as an ungrounded network.
A characteristic of an ungrounded system is that the active conductors have no connection to ground. Enclosures of the electrical systems are still grounded. Figure 1 shows the simplified schematic structure of an industrial battery energy storage system - consisting of the core components batteries, battery management system (BMS), inverter and transformer. All yellow components concern the monitoring technology.
The electrical network is designed as an ungrounded system. The active AC and DC conductors have no connection to the ground. Note: The grounding of the devices is not shown here.