According to the green growth and carbon-neutral policy in Korea, the installation of large-capacity ESSs is rapidly being increased, but a total number of 50 ESS fire cases have occurred since the end of 2023. ESSs are typically composed of series-parallel connections with numerous Li-ion batteries, and when the temperature of a deteriorated cell increases due to thermal, electrical, and mechanical stress, thermal runaway can occur due to additional heat generated by an internal chemical reaction. Here, an internal chemical reaction in a Li-ion battery results in the different characteristics on the decomposition reaction and heat release depending on the operation conditions in the ESS, such as the rising temperature rate, convective heat transfer coefficient, and C-rate of charging and discharging. Therefore, this paper presents mathematical equations and modeling of thermal runaway, composed of the heating device section, heat release section by chemical reaction, chemical reaction section at the SEI layer, chemical reaction section between the negative and positive electrodes and solvents, and chemical reaction section at the electrolyte by itself, based on MATLAB/SIMULINK (2022), which were validated by a thermal runaway test device. From the simulation and test results based on the proposed simulation modeling and test device according to the operation conditions in ESSs, it was found that the proposed modeling is an effective and reliable tool to evaluate the processing characteristics of thermal runaway because the occurrence time intervals and maximum temperatures had almost the same values in both the test device and simulation modeling. Accordingly, it was confirmed that the rising temperature rate and the convective heat transfer coefficient were more critical in the thermal runaway than the C-rate of charging and discharging.

This paper deals with the operation method of an intelligent fault isolation device (IFID), which can detect and estimate faults in rapid and accurate ways considering the slope characteristics of fault currents with distribution line constants. Namely, the proposed operation method in IFID calculates the slope of the fault current with distribution line constants, and reduces its operation time by comparing the calculated slope value to the setting value to detect and evaluate the fault condition. Moreover, this paper implements the DC 400 V, 10 kW scaled IFID consisting of hardware (H/W) and software (S/W) sections based on the proposed operation method. The H/W section is composed of main and current limit switches, a current limit resistor, voltage and current sensors, and switching mode power supply (SMPS). Also, the S/W section consists of a control board and code composer studio (CCS) to calculate the slope characteristics of the fault current and control the semiconductor device. From the test results based on the proposed operation method, it was found that the IFID considering the slope characteristics of fault currents can detect and evaluate the fault condition and limit the fault current faster than the existing method to consider the fault current only.

As many renewable energy sources have been waiting to be interconnected with distribution systems due to the lack of power system infrastructure in Korea, studies to solve the delayed problem for renewable energy sources required. In order to overcome these problems, this paper presents an introduction model and optimal capacity algorithm of a VPL (virtual power line) device, which is a virtual power line operation technology to manage the power system by operating an ESS installed at the coupling point of renewable energy source without additionally expanding the power system infrastructure in a conventional way; this paper also proposes an economic evaluation method to assess the feasibility of the VPL device. The optimal capacity of the VPL device is determined by solving the over-voltage problem for the customer, and the economic evaluation method for the VPL device is considered by cost and benefit elements to evaluate the feasibility of introduction model for VPL device. From the simulation result of the proposed optimal capacity algorithm and economic evaluation method based on the introduction model in the VPL device, and it was confirmed that the optimal kW capacity of VPL device was selected as the maximum value in power control values, and the optimal kWh capacity was also determined by accumulating the power control values over the time intervals; also, the proper capacity of the VPL can be more economical than the investment cost of power system infrastructure expansion in the conventional method.

This paper deals with an optimal operation method for surge protective devices (SPDs) to calculate the maximum continuous operating voltage (U_C) and the voltage protection level (U_P) by considering the sum of the voltage protection level and the dielectric continuous voltage limit of surge protective devices in order to effectively protect energy storage system (ESS) from switching and lightning surges. This paper also implements a test device for SPDs in ESSs based on the concept of a lightning electromagnetic surge protection measurement system (LPMS) by combining an SPD coordinated with spatial shielding with an ESS configuration. Here, the test device for the SPD in the ESS is composed of a power distribution unit (PDU), uninterruptible power supply (UPS), and a lightning electromagnetic pulse (LEMP) protection device, which combines two units of SPDs and disconnection switches (DSs) connected in parallel with two units of main circuit breakers (MCBs) and noise cut transformers (NCTs) connected in series. From the test results based on the proposed optimal operation method and test device, it is clear that the residual voltage with a third-class combination waveform can be kept within 1.5 kV of the surge voltage limit in all test scenarios, and it is confirmed that the proposed test device for SPDs can protect ESSs from switching and lightning surges. Therefore, it is confirmed that the SPD tested using the proposed method can effectively reduce switching and lightning surges, while the existing SPDs installed in ESS sites cannot protect ESSs from such surges.