Resistors and Capacitors in Series Mid-Point Grounding for Protection Application in Unipolar Low Voltage DC System

Abstract

With climate anomalies and ecosystem destruction caused by global warming, reducing carbon emissions is becoming increasingly important. Consequently, the power industry is investing in new sectors such as expanding renewable energy and utilizing DC grids to enhance energy efficiency and reduce coal fuel usage. The use of DC systems for carbon emission reduction is expected, and low-voltage direct current (LVDC) systems are continuously being investigated as efficient power systems. Existing studies have primarily focused on power conversion design and operation, but studies on the protection system configuration for the electrical safety of end users are insufficient. Therefore, this study analyzes the characteristics of resistors and capacitors in series (RCS) mid-point grounding in uni-polar LVDC systems for use at the end of LVDC systems and reviews protection systems against electrical shock and ground faults using DC residual current devices (DC-RCDs) and insulation monitoring devices (IMDs). Through fault tests, the appropriateness of using the protection system with these devices in RCS mid-point grounding configurations is verified. The fault test demonstrated that the RCS mid-point grounding LVDC system could detect and protect against faults within 80 ms using a DC-RCD. Additionally, it was confirmed that faults could be detected and cleared within 4 min using an IMD in the event of a high-resistance fault, enabling the use of IMD which was not feasible in grounding systems. Our research results contribute to the use of LVDC systems by establishing a protection system based on relatively inexpensive mechanical circuit breakers instead of high-cost semiconductor-based breakers often mentioned for consumer protection devices.

Keywords

• DC-RCD
• electrical safety
• electrical shock
• IMD
• LVDC
• mid-point