Residual Current Analysis and Residual Current Device Installation in Non-Isolated Uninterruptible Power Supply Systems

Residual current measurement has become increasingly important to ensure safety and reliability in power conversion systems. Conventional residual current devices (RCDs) are typically installed at the input of end-user equipment where they only monitor load-side leakage currents. However, uninterruptible power supply (UPS) systems inherently generate additional residual currents due to multiple conversion stages, including those from rectifiers DC-DC converters with batteries and inverters. This study investigates the residual current characteristics of UPS systems, and the effectiveness of RCD installation at different locations, such as the input, output, battery, and ground conductors, it discussed. Experimental verification using a 100 kW UPS prototype demonstrates that the detection performance significantly depends o the sensor position. Results provide practical guidelines for designing effective residual current monitoring schemes in UPS-based critical infrastructure, such as data centers.