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.

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.