Refinement of Recloser Operation and Safety Enhancement in Distribution Systems: A Study Based on Real Data

Abstract

This study analyzes recloser operation in the South Korean distribution system to propose effective operational strategies for improving safety and efficiency. This research is based on actual data, such as recloser operation data and fault statistics provided by the Ministry of the Interior and Safety and the Korea Electric Power Corporation, without the use of simulation tools or experiments. Key operational elements, such as reclosure counts, sequence settings, and high-current interruption features, were analyzed. First, an analysis of reclosure counts revealed that over 73% of faults were cleared after the first reclosure, and when the second reclosure was included, more than 90% were successfully restored. This finding suggests that reducing the number of reclosures from the standard three to one or two would not significantly impact fault restoration performance while simultaneously reducing arc generation, thereby improving safety. Additionally, a review of recloser sequence settings highlighted the fact that the traditional 2F2D (two fast, two delayed) sequence often led to frequent instantaneous tripping, increasing the risk of arc generation. The 1F1D (one fast, one delayed) sequence, which applies a delayed trip after an initial fast trip, offers a better fault-clearing performance and reduces the risk of arc generation. Lastly, an analysis of the high-current interruption feature suggested that enabling this function for faults with low reclosing success rates, particularly in cases of short-circuit faults, and setting an immediate trip threshold for fault currents exceeding 3 kA would enhance both safety and efficiency. This operational strategy was implemented in the South Korean distribution system over a three-year period, starting in 2021. While there was a 2.1% decrease in reclosure success rates, this strategy demonstrated that similar success levels could be maintained while reducing the number of reclosures, thus mitigating equipment damage risks and improving safety measures. The refined recloser operation plan derived from this study is expected to enhance the overall stability and reliability of distribution systems.

1. Research Background and Necessity

A recloser is an automated device used in distribution systems that temporarily interrupts the current during a fault and recloses after a set period to determine whether the fault is temporary. This allows for quick restoration of power in the case of temporary faults and plays a critical role in maintaining the continuity of the power grid. However, the arc generated during the reclosing process can cause damage to electrical equipment, and the intense heat and noise produced during high-current faults can in severe cases result in fires. For instance, in the 2019 wildfire in Goseong, Gangwon Province, South Korea, a spark caused by the operation of a recloser was spread by strong winds, leading to extensive damage. This incident highlights the importance of prioritizing safety alongside fault recovery during recloser operation.

Conventional recloser operation strategies mainly focus on minimizing power outages and resuming the power supply quickly, with most reclosers configured to allow up to three reclosing attempts. While this approach enables swift restoration of power in the case of temporary faults, it also increases the risk of arc generation during repeated reclosing attempts. Additionally, failure to clear the fault can lead to larger incidents. Moreover, applying a fixed sequence and reclosing interval without considering the type or cause of the fault results in inadequate responses to specific fault conditions. In cases where high currents are generated due to reclosing failures, the increased arc energy can severely damage electrical equipment and exacerbate the impact of the fault.

To address these issues, various studies have been conducted. Reference [1] used PSCAD/EMTDC simulation software to analyze secondary arc currents during single-pole recloser operations on extra-high voltage (EHV) lines. The study proposed an optimized relationship between reclosing time and voltage recovery at the fault location to reduce arc extinction time. Reference [2] utilized a genetic algorithm (GA) to optimize the coordination between the reclosers and fuses in a radial distribution system with distributed generation (DG). The study evaluated coordination performance under various settings and proposed optimal recloser-fuse coordination values to maximize system protection. Reference [3] modeled various fault scenarios in distribution systems using EMTP-RV simulations to assess the negative impact of recloser operations on power transformers. The study analyzed the electrical stress imposed on transformers and protective equipment due to repeated recloser operations and proposed optimal operational patterns and coordination methods to mitigate these effects. Reference [4] combined GA with particle swarm optimization (PSO) in a hybrid optimization technique to determine the optimal locations for reclosers and sectionalizers. Reference [5] used Monte Carlo simulations to evaluate the effectiveness of reclosers in protecting blind zones in distribution networks with DG. The study proposed optimal recloser settings that enhance blind zone protection performance. Reference [6] proposed a novel algorithm to reduce the malfunctions of recloser control devices by resolving coordination issues between protective relays and reclosers. The proposed algorithm analyzed conditions that could lead to malfunctions and derived dynamic coordination parameters to prevent them. Reference [7] provided recloser setting strategies based on various operational scenarios. The study modeled recloser operations according to fault types in distribution networks, proposing methods to minimize the risk of arc generation while maintaining system stability. Reference [8] proposed automatic reclosing settings and operational methods for different fault types. The study performed simulations using PSCAD to analyze the correlation between post-fault voltage recovery time and reclosing attempts, proposing optimal reclosing times to minimize the risk of arc reignition. Reference [9] comprehensively reviewed automatic recloser control methodologies to enhance the reliability of the distribution networks. The study compared and analyzed existing control methodologies, evaluated their performances through simulations, and derived optimal control strategies. Reference [10] proposed various techniques to mitigate arc flash incidents in power systems. This study focused on recloser settings and the coordination between protective devices to reduce arc energy and occurrence frequency. The study in [11] focused on analyzing adaptive single-pole auto-reclosing techniques for EHV transmission lines, utilizing secondary arc voltage and harmonics to distinguish between temporary and permanent faults. It also adjusted the reclosing timing by detecting zero-sequence voltage and harmonic distortion. In [12], a comprehensive review of the auto-reclosing techniques for AC, DC, and hybrid systems was conducted, with particular attention given to AC/DC hybrid-system faults, and adaptive control methods were proposed based on fault types and system conditions. For [13], an adaptive auto-reclosing method based on harmonic distortion and THD analysis was proposed, differentiating fault types and determining the optimal reclosing timing based on secondary arc occurrences. Meanwhile, Ujjaval et al. [14] introduced an adaptive dead-time control strategy for EHV lines, which replaced fixed dead times with real-time monitoring of fault voltage and current to dynamically adjust reclosing timings and improve performance. The research in [15] focused on detecting secondary arcs in EHV lines and automatically determining when to reclose by detecting arc extinction. On the other hand, [16] developed a numerical algorithm for medium-voltage transmission lines to automate reclosing for temporary faults and prevent reclosing for permanent faults, using harmonic analysis and voltage fluctuation detection to optimize reclosing timing. Building upon these, Jannati et al. [17] proposed an adaptive single-pole auto-reclosing method utilizing zero-sequence voltage to analyze fault characteristics and dynamically determine reclosing timing. Lastly, Elkalashy et al. [18] presented a method based on zero-sequence power, which detected power flow changes to differentiate between temporary and permanent faults, analyzing the fault current and voltage fluctuations to determine the best reclosing time.

Existing studies have made significant contributions to improving recloser operations, but there are still areas for improvement. First, most studies have focused on specific scenarios rather than fully addressing real-world operational data from distribution systems. Second, the practical application and validation of the proposed methods are somewhat limited. Third, using additional equipment can introduce economic challenges. Because recloser operation standards should adapt to the distribution system’s environment, applying and analyzing these methods in real power systems is essential.

In response, this study analyzed actual data from the South Korean distribution system without requiring additional equipment, focusing on key operational elements such as reclosing count, sequence settings, and high-current interruption features. A new set of operational standards for reclosers was developed, and these methods were applied to the entire Korean distribution network, with a three-year period of analysis and validation. This study is expected to improve safety and reliability as compared to existing methods, ultimately contributing to the stable operation of electrical systems, preventing large-scale accidents, and reducing societal costs.

The composition of this paper is as follows: Section 2 provides an analysis of the current recloser operation practices in South Korea. Section 3 builds on this analysis to describe the proposed recloser operation method. Section 4 presents the verification of the proposed method through practical validation. Finally, Section 5 concludes with the findings and implications of this study.

2. Analysis of Recloser Operational Elements

This study comprehensively analyzes the key elements of recloser operations to derive refined operational strategies. The main elements analyzed include the number of reclosing attempts, sequence settings, and high-current interruptions. Based on actual operational data provided by the Ministry of the Interior and Safety and the Korea Electric Power Corporation, a detailed review was conducted without the use of additional simulation tools, relying solely on data-driven analysis to propose operational methods that consider both the safety and efficiency of the distribution system.

2.1. Reclosing Count

The reclosing function of a recloser plays a critical role in the distribution system by temporarily interrupting the faulted section and resuming the current after a set time to determine whether the fault is temporary or permanent. This feature is advantageous for quickly restoring service when the fault is temporary and caused by external factors (e.g., tree branches, momentary wire contact, etc.). If the reclose is successful, the faulted section is restored, and the power supply resumes. If the reclose fails, the system proceeds to the next stage of fault interruption and reclosing procedures.

As shown in

Table 1. Status of recloser reclosing settings (Korea, 2018).

Reclosing Count	1	2	3	Total
Quantity	94	1245	8056	9395
Share (%)	1%	13%	86%	100%

, approximately 86% of reclosers in the South Korean distribution system were configured for three reclosing attempts as of 2019. Only 1% were set for one reclosing attempt, while 13% were set for two reclosing attempts. This high number of reclosing attempts maximizes the likelihood of restoring power in the case of temporary faults, offering a significant advantage for system reliability. However, if the fault is not cleared, repeated reclosing attempts increase the risk of arc generation, which can result in significant damage to electrical equipment and raise the potential for electrical fires caused by the arcs.

In particular, in severe faults such as short circuits, additional reclosing attempts after the first failure may pose greater risks. Repeated reclosing in such cases not only leads to unnecessary arc generation but can also exacerbate physical damage to electrical equipment. Therefore, it is essential to adjust the number of reclosing attempts based on the type and cause of the fault. In certain cases, reducing the number of reclosing attempts may be necessary to prevent further hazards. This strategic adjustment enhances the operational efficiency of reclosers while reducing the risk of accidents.

2.2. Recloser Sequence

The recloser sequence refers to the series of steps a recloser takes when a fault occurs, typically involving a combination of instantaneous and delayed tripping. Instantaneous tripping interrupts the current immediately after a fault occurs to minimize arc generation, while delayed tripping occurs after a certain time interval to enhance coordination with protective devices.

In South Korea, most reclosers are configured with a 2F2D (two fast, two delayed) sequence, as illustrated in Figure 1, with approximately 83% of all reclosers operating under this default sequence, as shown in

Table 2. Distribution of recloser sequences (Korea, 2018).

Reclosing Count	Single Reclosing		Double Reclosing		Triple Reclosing		Total
	2F	1F1D	2F1D	1F2D	2F2D	1F3D
Quantity	94	1245	8056	1%	13%	86%	9395
Share (%)	0.2%	0.8%	13.3%	0.9%	83.3%	1.4%	100%

. This configuration aims for rapid fault recovery, in which the fault is cleared by the initial two fast trips. If the fault is not cleared, the delayed tripping steps in to handle the fault more safely.

However, while the 2F2D sequence is effective for quickly addressing faults, frequent use of instantaneous tripping increases the likelihood of arc generation. Additionally, delayed tripping can be prone to malfunctions due to inrush currents, and overly long delayed tripping settings may prolong the fault recovery time. To address these issues, it is necessary to reconsider the combination of sequences and adjust them according to the situation.

2.3. High-Current Interruption in Reclosers

High-current interruption is a function in which the recloser permanently cuts off the faulted section when a current exceeding a preset threshold is detected. This feature plays a crucial role in preventing equipment damage and secondary incidents, such as fires, by cutting off the circuit when the fault currents are extremely high, which would otherwise cause a rapid increase in arc energy.

However, most reclosers in South Korea currently operate with the high-current interruption feature deactivated. This approach is intended to maximize the use of reclosing attempts to automatically restore service in the event of a fault. When this feature is disabled, the recloser continues to attempt reclosing even when the fault current is extremely high. Consequently, the risk of arc generation increases as the fault current persists, which can lead to equipment damage and, in severe cases, fires. In particular, during severe faults such as short circuits, high-current interruption is essential. However, when the feature is deactivated, these risks cannot be mitigated in a timely manner. Therefore, activating the high-current interruption function when the fault current exceeds a certain threshold would significantly improve safety.

3. Proposed Recloser Operation Methods

The proposed recloser operation method is specifically designed to maximize practical field applicability without requiring additional infrastructure investments or complex computational resources. Previous studies often necessitated the installation of high-performance and costly sensors for precise data acquisition or rely on high-performance computers and edge computing devices to handle real-time data analysis. For instance, to continuously monitor high-resolution current and voltage data, new precision sensors may be required, while real-time data processing might demand edge devices deployed on-site. While these approaches contribute to data accuracy and monitoring precision, the investment required for such high-cost equipment and computational resources can be a significant barrier within distribution system environments, limiting their widespread implementation.

In contrast, this study proposes a recloser operation method that leverages the statistical analysis of existing data to enhance both economic efficiency and safety without requiring additional equipment. By utilizing straightforward statistical models to analyze data already collected by existing infrastructure, the proposed approach minimizes reliance on high-cost sensors or additional edge-computing devices, thus focusing on maximizing field applicability within realistic operational constraints. Consequently, the proposed method reduces the demand for supplementary equipment and computational resources, providing a practical solution that can be readily implemented in distribution systems with limited infrastructure investment. This case report emphasizes the practicality and scalability of the proposed method, offering an innovative approach to improve recloser operation within distribution system environments, enhancing both safety and economic efficiency without the need for additional infrastructure.

In this study, therefore, we propose refined strategies for the key operational elements of reclosers—reclosing count, sequence, and high-current interruption—to enhance safety and reliability. Each proposal is based on the current operational conditions and their associated issues, with the aim of improving operational efficiency and strengthening equipment protection in the future. The methodology we approach in this study is illustrated in Figure 2 below.

3.1. Reclosing Count

Currently, most reclosers are configured for three reclosing attempts, ensuring a high fault restoration rate when faults occur. However, this approach increases the frequency of arc generation, thereby elevating the risk of equipment damage and the potential for additional safety incidents due to repeated reclosing attempts. As a result, this study examines the possibility of reducing the number of reclosing attempts to enhance equipment safety and minimize unnecessary fault restoration attempts.

First, a statistical analysis of fault clearing through reclosing attempts was conducted, as shown in

Table 3. Status of fault automatic clearing by reclosing (Korea, 2018).

Reclosing Count	Successful Reclosing				Failed Reclosing	Total
	Single Reclosing	Double Reclosing	Triple Reclosing	Subtotal
Quantity	3858	809	85	4752	506	5258
Share (%)	73.4%	15.4%	1.6%	90.4%	9.6%	100%

. The analysis revealed that more than 73% of faults were restored after a single reclosing attempt, and over 90% were restored after two attempts. In contrast, the third reclosing attempt contributed minimally to fault restoration, with 4667 out of 4752 cases (approximately 98.21%) already resolved within two attempts. This finding suggests that most faults can be resolved with one or two reclosing attempts, rendering the third attempt unnecessary.

A detailed analysis of reclosing success rates by fault cause, region, and season is presented in Figure 3. Although there were some differences in the reclosing success rates based on the cause of the fault, the improvement in fault clearing between the second and third reclosing attempts was not significant. Similarly, the regional and seasonal analyses showed no meaningful differences between the second and third reclosing attempts, with a success rate of over 70% achieved after just the first reclosing attempt in all cases. Based on these findings, it was concluded that satisfactory fault restoration can be achieved with one or two reclosing attempts rather than persisting with three. Reducing the number of reclosing attempts from three to one or two is therefore deemed a reasonable choice, and the first reclosing attempt is considered the most suitable for minimizing arc generation and enhancing equipment safety.

However, beyond the statistical analysis, it is also necessary to assess the broader impacts of reducing the number of reclosing attempts from the current three to the proposed one or two, particularly in terms of power quality. The key indicators to be analyzed are the number of momentary outages and the average outage duration per household based on the number of reclosing attempts. These indicators were calculated using the total of 4752 fault-clearing cases via reclosing, as specified in Table 3, which presents the status of fault-clearing by reclosing.

As shown in

Table 4. Impact analysis of changing reclosing attempts (Korea, 2018).

		Single Reclosing	Double Reclosing	Triple Reclosing
Fault Clearing via Reclosing		4752	4667	3858
Power Quality	Momentary Outages (Cases)	506	591	1400
	Average Outage Duration per Household (Minutes)	2.73	2.85	3.98

, reducing the number of reclosing attempts from the current three to two resulted in an increase of 85 momentary outages, but the average outage duration per household increased by only 0.12 min (approximately 7.2 s), indicating a minimal impact. Additionally, when the number of reclosing attempts was reduced to one, there was an increase of 894 momentary outages, but the average outage duration per household increased by only 1.25 min (approximately 75 s), showing a limited effect. This suggests that reducing the number of reclosing attempts to one or two could prevent safety incidents, such as arc generation, while causing no significant increase in outages.

The refined reclosing count proposed in this study is based on the analysis of existing data and aims to achieve a balance between fault restoration performance and safety. However, additional field tests and long-term monitoring would yield more reliable results. Furthermore, the long-term impact of reducing the number of reclosing attempts on fault restoration performance should be analyzed more thoroughly as more data is accumulated over time. This study provides a foundational model for such analyses, which can be further refined in future research. While this study addresses the impact of reducing the number of reclosing attempts on power quality to improve safety, future research will explore the correlation between various fault scenarios and fault restoration speeds.

3.2. Recloser Sequence

To determine the most effective recloser sequence settings, the operational statuses of the reclosers in South Korea were analyzed, as shown in

Table 5. Status of recloser operating sequences (Korea, 2018).

	1F1D	1F2D	1F3D	2F	2F1D	2F2D	Total
Quantity	78	83	135	16	1162	7921	9395
Share (%)	0.8%	0.9%	1.4%	0.2%	13.4%	83.3%	100%

. The analysis revealed that the recloser sequences are composed of various combinations, including 1F1D (F-D), 1F2D (F-D-D), 1F3D (F-D-D-D), 2F (F-F), 2F1D (F-F-D), and 2F2D (F-F-D-D). Out of a total of 9395 reclosers, 83.3% (7921 units) were configured with the 2F2D sequence. Additionally,

Table 6. Status of recloser operating sequence settings by type (Korea, 2018).

	First Fast Trip	1st Reclosing	2nd Reclosing	3rd Reclosing
Fast Trip	-	9099	0	0
Delayed Trip	-	296	9166	8056

summarizes these sequences by type. The results show that in the first reclosing attempt, 9099 reclosers used instantaneous tripping, while 296 reclosers employed delayed tripping. The remaining second and third reclosing attempts were uniformly configured with delayed tripping.

However, the recloser must always perform at least one instantaneous trip during the first operation, and it is recommended that at least one delayed trip be executed to ensure coordination with the fuses and prevent malfunctions caused by inrush currents. Accordingly, this study analyzed various combinations, taking these constraints into account. Considering these limitations, we analyzed the following combinations: ① instantaneous trip followed by another instantaneous trip (F-F), ② instantaneous trip followed by a delayed trip (F-D), and ③ instantaneous trip followed by consecutive delayed trips (F-D-D), as shown in

Table 7. Fault-clearing success rate by fault type based on sequence combinations (Korea, 2019).

		Unknown	Human Error	Equipment Failure	External Contact	Customer-Induced Fault	Natural Phenomena	Poor Construction	Total
F-F	Success	840	84	314	1071	832	555	10	3706
	Fail	105	38	120	162	147	68	1	641
	Rate	86%	62%	65%	83%	80%	86%	91%	85%
F-D	Success	32	3	21	55	18	11	8	152
	Fail	5	1	3	3	1	1	1	15
	Rate	88%	75%	88%	95%	95%	92%	89%	91%
F-D-D	Success	132	38	163	197	193	86	-	809
	Fail	13	14	6	30	11	10	1	85
	Rate	91%	73%	97%	87%	95%	90.7%	-	91%

and Figure 4.

As shown in Table 7, the fault-clearing success rate for the F-D sequence was higher than that of F-F. Additionally, when examining the F-D-D sequence, there was no significant improvement in the fault-clearing success rates as compared to F-D. Specifically, when analyzing success rates by fault cause, the F-F sequence exhibited high success rates for faults caused by unknown reasons, natural phenomena, and installation errors. However, for the faults caused by human error or equipment failure, the success rates were lower. In contrast, the F-D sequence demonstrated a stable fault-clearing success rate across all fault types, showing a notable difference. Particularly, because faults caused by human error and equipment failure accounted for 17% of all faults, and these faults had lower success rates under the F-F sequence, it was concluded that the F-D sequence is more appropriate. Therefore, based on this analysis, F-D is considered the most suitable recloser sequence setting.

The 1F1D sequence setting proposed in this study was derived from the initial data analysis and showed improvement in fault clearing performance. As more field data on reclosing sequence settings becomes available in the future, it is expected that this will serve as an important foundation for developing customized sequences according to fault types.

3.3. High-Current Interruption in Reclosers

As mentioned earlier, high-current interruption is a function in which the recloser permanently cuts off the faulted section when a current exceeding a preset threshold is detected. Although high-current interruption is currently deactivated in Korea to maximize the use of reclosing, it is necessary to activate permanent interruption when a high fault current is detected for safety reasons.

However, the challenge lies in defining “high current”. Because fault current values can vary depending on the fault’s location, type, and resistance, it is difficult to establish a uniform standard. Therefore, this study aims to set targets and criteria for high-current interruption by selecting faults with high fault currents and low reclosing success rates, considering the size of the fault currents and the frequency of different fault types.

Table 8. Fault current by fault type (Korea, 2018).

	Fault Current	<1 kA	1~2 kA	2~3 kA	3~4 kA	4~5 kA	5~6 kA	>6 kA	Total
Ground Fault	Quantity	2284	1348	403	175	92	19	4	4325
	Share	52.80%	31.17%	9.32%	4.05%	2.13%	0.44%	0.09%	100%
	Cumulative Share	52.80%	83.98%	93.3%	97.35%	99.48%	99.92%	100%	100%
Short Circuit	Quantity	261	327	181	88	56	23	-	936
	Share	27.88%	34.94%	19.34%	9.4%	5.98%	2.46%	-	100%
	Cumulative Share	27.88%	62.82%	82.16%	91.56%	97.54%	100%	-	100%

summarizes the fault current sizes by fault type, while

Table 9. Reclosing success rate by fault type (Korea, 2018).

		Successful Reclosing				Failed Reclosing	Total
		Single Reclosing	Double Reclosing	Triple Reclosing	Subtotal
Ground Fault	Quantity	3424	633	64	4151	174	4325
	Share	79%	15%	2%	96%	4%	100%
Short Circuit	Quantity	434	146	21	601	332	933
	Share	46%	16%	2%	64%	36%	100%

shows the reclosing success rates by fault type. As indicated in Table 8, out of a total of 5258 faults in 2019, 4325 were ground faults, and 936 were short-circuit faults. In terms of the distribution of fault types, approximately 84% of ground faults (3632 out of 4325) had fault currents of 2kA or less. For short-circuit faults, as shown in Figure 5, approximately 82% (769 out of 936) had fault currents of 3 kA or less. Furthermore, as indicated in Table 9, the reclosing success rate for ground faults, even considering up to three reclosing attempts, was very high at 96%. In contrast, for short-circuit faults, the reclosing success rate remained much lower at 64%, even after three reclosing attempts.

Taking the two considerations mentioned above into account, the following conclusions were drawn. First, the target for the high-current interruption function was set for short-circuit faults. Unlike ground faults, the success rate of reclosing for short-circuit faults is significantly lower. Ground faults are more likely to be successfully cleared through reclosing, with a success rate of 96%, according to Table 9. However, the reclosing success rate for short-circuit faults is much lower at 64%, which increases the likelihood of safety issues such as arc generation during the reclosing process. Therefore, rather than attempting reclosing for short-circuit faults, it is safer and more efficient to activate the high-current interruption function to immediately cut off the faulted section.

Next, based on the results shown in Table 8, the threshold for defining “high current” was set at 3 kA, which covers approximately 82% of all fault currents. While it would be ideal to prepare for all fault scenarios, considering operational costs and equipment lifespan, setting the threshold at 3 kA is more practical. References [19,20,21] indicate that designing a system to handle all possible faults can be prohibitively expensive, and it is more realistic to meet common fault patterns. From this perspective, 3 kA was set as a cost-effective standard.

However, the 3 kA threshold proposed in this study is derived from statistical analysis, and the criteria for high-current interruption may vary depending on the fault type. Therefore, more refined criteria based on fault types may be necessary, which will be supplemented through further data collection.

4. Validation of the Proposed Method

To validate the recloser operation strategy proposed in this study, we applied the strategies for reclosing count, operation sequence, and high-current interruption to more than 13,000 distribution lines in South Korea and analyzed their feasibility. Because the proposed method was implemented across the entire distribution network in South Korea as of 2021, the analysis was conducted using data from 2021 to 2023.

Earlier, we concluded that setting the reclosing count to one or two attempts is appropriate, and that the 1F1D (F-D) sequence is the most suitable. However, as indicated in Table 7, the analysis of the reclosing success rates by sequence combinations was limited to 152 cases in 2019 due to the small number of reclosers operating under the F-D sequence at that time. Therefore, it is necessary to reanalyze the reclosing success rates of F-F and F-D sequences based on the three-year dataset, including the year 2021, when F-D was applied to the entire distribution network in Korea. Additionally, because the high-current interruption function was applied to short-circuit faults, the analysis focused on ground faults for consistency in the results.

As shown in

Table 10. Reclosing success rate by reclosing sequence (F-F vs. F-D).

	2019	2021	2022	2023	Average (2021~2023)
Recloser Sequence	F-F	F-D	F-D	F-D	F-D
Reclosing Success	3706	5057	4692	3930	4559.7
Reclosing Failure	641	735	933	1045	904.3
Reclosing Count	4347	5792	5625	4975	5464
Reclosing Success Rate	85.3%	87.3%	83.4%	78.9%	83.2%

, in 2019, using the existing F-F sequence, the number of successful reclosing attempts was 3706, with 641 failures, resulting in a total of 4347 reclosing attempts and a success rate of 85.3%. In contrast, starting from 2021, the proposed F-D sequence was applied. During this period, the average number of successful reclosing attempts was 4559.7, with an average of 904.3 failures, resulting in a total average of 5464 reclosing attempts. The reclosing success rates were 87.3% in 2021, 83.4% in 2022, and 78.9% in 2023, averaging 83.2%, indicating an improvement in success rates as compared to the previous method, as shown in Figure 6.

Notably, the reclosing success rate in 2021 was the highest at 87.3%, which can be attributed to the immediate effects of introducing the F-D sequence, including the system improvements, enhanced equipment inspections, and improved training of operational personnel. Compared to the traditional method, a 2.1% decrease in the reclosing success rate was observed. However, this decline is not considered statistically significant. Despite enhancing safety measures such as reducing the occurrence of arcs by lowering the number of reclosing, the proposed method maintained a comparable level of reclosing success rate.

5. Conclusions

This study comprehensively analyzed key operational elements such as the number of reclosing attempts, sequence settings, and high-current interruptions based on real data from reclosers operating in South Korea’s distribution system, with the goal of improving recloser operation. Through this analysis, we proposed specific strategies to enhance safety and minimize physical damage to power equipment.

First, the analysis of reclosing attempts showed that approximately 73% of faults were restored after the first reclosing attempt, and a total of around 90% were restored after the second attempt. Therefore, reducing the number of reclosing attempts to one or two has a limited impact on fault restoration performance, while also reducing the risk of equipment damage and the likelihood of arc generation, thereby enhancing safety. This reduction is expected to lower the risk of major accidents caused by equipment damage and contribute to reducing societal costs. Further research on fault restoration performance will be conducted based on long-term field tests and accumulated data.

Second, the analysis of sequence settings revealed that the existing 2F2D sequence was widely applied to many reclosers. However, this setting increased the likelihood of arc generation due to the frequent occurrence of instantaneous tripping. In contrast, the 1F1D sequence, which applies delayed tripping after the first instantaneous trip, was found to provide a stable fault-clearing performance. Additional tests will be conducted that consider various fault scenarios and climate conditions, and customized sequences for different fault types will be developed.

Third, the analysis of the high-current interruption function confirmed that applying this function to short-circuit faults with low reclosing success rates is appropriate. Additionally, statistical analysis suggested that activating the high-current interruption function for fault currents above 3 kA could cover approximately 82% of all faults. Further data collection is needed to establish more detailed criteria by fault type, and these findings will be used to refine high-current interruption settings.

Finally, because the proposed strategies were applied to South Korea’s distribution network starting in 2021, the average reclosing success rate showed a decrease of approximately 2.1%. However, this result indicates that the proposed strategies have successfully maintained a comparable level of reclosing success rates, despite reducing the number of reclosing to enhance safety measures, such as mitigating arcs. Future efforts will focus on further refining recloser operation strategies to improve the overall system efficiency.