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.

Frequency response performance in power systems is becoming vulnerable due to the transition toward the higher penetration of renewable energy such as achieving carbon neutrality. In particular, reducing power system inertia energy as the asynchronous generation increases could result in violating the frequency stability constraint when a disturbance occurs in the power systems. In order to control the rapidly fluctuating frequency of the power system with low inertia, it is necessary to introduce fast frequency response resources such as a Battery Energy Storage System (BESS). This paper proposes a method to calculate the required capacity of BESS for compensating the frequency control performance of the power system using inertia energy. For calculating the required capacity of BESS, the inertia energy in the critical power system, where frequency control performance marginally satisfies frequency stability constraint, should be calculated. Also, the inertia energy in the evaluated power system having deficit inertia energy should be calculated. By comparing power systems that respond with different dynamics when the same disturbance occurs, the proposed calculation corresponds to the ratio of inertia energy deficiency based on critical power system inertia energy within the power imbalance. Through various case studies employing Korean power systems, the effectiveness of the inertia energy-based calculation method for the required BESS is verified by the fact that the BESS integrated power system marginally satisfies the frequency stability constraint. In these study cases, it is found that the instant response of BESS is very effective for compensating the frequency control performance of the low inertia power system. By applying the proposed method, it is also found that about 840 MW of BESS can achieve carbon neutrality in the Korean power system.

Low-voltage direct current (LVDC) systems have been increasingly studied as new efficient power systems. However, existing studies have primarily focused on power conversion designs, control, and operation, and research on ground configurations of LVDC systemsis insufficient. Consideration of the installation criteria of protective equipment and grounding systems is crucial because ground configurations in general households for end users are highly associated with the risk of human electrocution. Therefore, we investigate a mid-point grounding system using capacitors to ensure electrical safety in a mono-polar LVDC system that a general end user can directly experience in a household. MATLAB/Simulink is used to analyze the fault characteristics of the mid-point grounding system using capacitors by considering the effects of DC on the human body based on the International Electrical Code (IEC). Consequently, this paper suggests the minimum required values of the capacitors and resistors to operate the DC residual current detector (DC RCD), and the operation of the DC RCD was confirmed. By confirming the applicability of DC RCD in a household LVDC system with a mid-point grounding system using capacitors and resistors, unnecessary power loss in a mid-point grounding system and electrical accidents, such as electric shocks and fires, could be minimized.

Corona discharge is a phenomenon wherein gas on the surface of electrical equipment is ionised. Severe ionisation can lead to insulation breakdown and cause equipment damage. Consequently, non-contact portable devices are employed to detect corona discharge in real time while the electrical equipment is pressurised. Recently, several devices capable of visualising corona discharge phenomena occurring in the ultrasonic region have been developed. However, these devices are primarily used for scanning purposes to verify the occurrence of partial discharge, as detailed guidelines for operating the equipment in real-world field conditions are yet to be established. Therefore, this study proposes a measurement technique for utilising ultrasonic corona imaging diagnostic equipment in the field. This technique involves the use of corona discharge electrodes and aged epoxy insulator samples. First, the performance of the ultrasonic corona imaging diagnostic equipment based on environmental conditions was evaluated by varying the distance, frequency, temperature, and humidity using the corona discharge electrodes. Then, parallel measurements were conducted with a high-frequency current transformer sensor on epoxy insulator samples subjected to simple ageing, cracking, and partial surface damage, and the results were analysed. Finally, an efficient measurement technique, including equipment operation procedures, was proposed by integrating the measurement results.