## 2 Standard Synopsis  
IEEE Std. 1547-2018 and KS C 8564:2021 are representative technical standards that include the latest grid support functions domestically and internationally. This section compares and analyzes the change in voltage/frequency regulation related to the prevention of islanding operation in these two technical standards and the non-detection zone for islanding operation. The major difference between the islanding detection requirements in IEEE Std. 1547-2018 and KS C 8564:2021 is that the required islanding prevention times are 2 s and 0.5 s, respectively. This difference comes from the technical specifications, such as the reclosing time to fault current of each country's power grid. In both standards, the grid code for abnormal voltage magnitude and frequency threshold value has changed as the proportion of DG increases in the power grid. Tables 1 and 2 show the clearing time of DG according to the abnormal voltage and frequency, respectively. Clearing time is defined as the time between the start of an abnormal condition and the DG ceasing to energize the connected grid. Table 1 shows the required clearing times for Over Voltage (OV), a voltage larger than the nominal voltage level, and Under Voltage (UV), a voltage smaller than the nominal voltage level. In the case of IEEE Std. 1547-2018, compared to the previous version, there was no change in the setting value of OV trip; only the clearing time was partially changed, and the setting value of UV trip was lowered, so the allowable range of grid connected operation was wider. In the case of KS C 8564, the UV trip setting value was found to be wider in the same trend. Table 2 shows the required clearing times for Over Frequency (OF), frequencies greater than the nominal frequency level, and Under Frequency (UF), lower than the nominal frequency level. In the case of IEEE Std. 1547-2018, the OF trip set value was 1.5 Hz wider, and the UF trip set value was wider by 2.8 Hz, compared to IEEE Std. 1547-2003, and the allowable range of grid-connected operation was wider. In the same trend, in the case of KS C 8564-2021, the OF trip set value was 1 Hz wider and the UF trip set value was 2.3 Hz wider compared to KS C 8564-2015, so the allowable range of grid-connected operation was wider. This is because a wider voltage/frequency setting was required to prevent the nuisance tripping of DGs, which occurs due to transient operations, such as the switching of capacitor banks and starting of motors. According to this trend, it becomes more difficult to prevent islanding operations with most inverter-based anti-islanding technologies, based on OV/UV/OF/UF relays. Equations (1) and (2) are quantitative analyses of the non-detection zones of islanding operations according to the voltage/frequency relay threshold values and are summarized in Table 3. By adopting the threshold values like \(V_{max}\), \(V_{min}\),\(f_{max}\), and \(f_{min}\) in Table 2 into Equations (1) and (2), quantitative non-detection zones are generated, as shown in Table 3. Since the amount of change in effective power for islanding operation detection must be \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Standard**} & \multicolumn{2}{c}{**OV1**} & \multicolumn{2}{c}{**OV2**} & \multicolumn{2}{c}{**UV1**} & \multicolumn{2}{c}{**UV2**} \\ \cline{2-9}  & **p.u.** & **Clearing Time [s]** & **p.u.** & **Clearing Time (s)** & **p.u.** & **Clearing Time (s)** & **p.u.** & **Clearing Time (s)** \\ \hline IEEE Std. 1547-2003 & 1.1 & 1 & 1.2 & 0.16 & 0.88 & 2 & 0.5 & 0.16 \\ IEEE Std. 1547-2018 & 1.1 & 2 & 1.2 & 0.16 & 0.7 & 2 & 0.45 & 0.16 \\ KS C 8564-2015 & 1.1 & 1 & 1.2 & 0.16 & 0.88 & 2 & 0.5 & 0.16 \\ KS C 8564-2021 & 1.1 & 1 & 1.2 & 0.16 & 0.7 & 2 & 0.5 & 5 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: DG response to abnormal voltage by the standards.