Characterization of the Airflow Distribution near a Circuit Breaker’s Cu-Ag-Alloy Electrode Surface during and after Breakdown

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

coatings-2828252

Characterization of Airflow Distribution near Circuit Breaker Cu-Ag-Alloy Electrode Surface when It Breakdown

 

This paper addresses a critical issue related to circuit breakers facing multiple lightning strikes post-tripping, leading to potential breakdowns and a shortened lifespan. The use of schlieren technique and image recognition technology to analyze the temperature diffusion process of the inrush current in circuit breakers is commendable.

 

1.    The introduction is concise but could benefit from a more detailed background explaining the significance of circuit breakers in power systems, the impact of lightning strikes, and the importance of understanding temperature characteristics.

2.    The research objectives could be explicitly stated to provide clarity on what the paper aims to achieve. Additionally, defining the scope of the study would help readers understand the limitations and applicability of the findings.

3.    The utilization of the schlieren technique and image recognition technology is well-justified. However, more details about the experimental setup, conditions, and any potential limitations should be provided to ensure the reproducibility of the results.

4.    The paper mentions obtaining temperature characteristics and airflow features, but the specifics of the data obtained and the methodology used for analysis are not clear.

5.    The statement about the generation of shock waves and airflow characteristics is intriguing. A more detailed discussion on the implications of these findings for circuit breaker design, operation, and potential issues faced during lightning strikes would strengthen the paper.

6.    Clarify how the shock wave velocity and airflow boundary diffusion velocity were measured. Additionally, providing context on how these characteristics relate to the circuit breaker's performance and potential breakdown would add depth to the analysis.

7.    The inverse proportionality of temperature change to the square of time is an interesting finding. Elaborate on the significance of this relationship and discuss how it can be utilized in practical circuit breaker design or maintenance strategies.

8.    The rapid decay of airflow boundary diffusion velocity is mentioned, but the implications of this decay on the circuit breaker's stability or susceptibility to further lightning strikes should be discussed.

9.    The concentration of maximum temperature between 6000 and 8000 K is noted. Provide insights into why this temperature range is critical and discuss its potential impact on the circuit breaker's material integrity.

10.  The conclusion should provide a concise summary of key findings and explicitly state how the results contribute to the design and optimization of circuit breakers. Additionally, suggest potential applications or future research directions based on the obtained insights.

Comments on the Quality of English Language

The linguistic level and the mechanics of English writing are not appropriate for publication. There are few grammatical and typing errors in the manuscript, so please check and revise. The way of writing is not clear and it is difficult for the readers to understand. The paper should be rewritten and proofread again thoroughly. Extensive editing of English language is required.

Author Response

Q1：The introduction is concise but could benefit from a more detailed background explaining the significance of circuit breakers in power systems, the impact of lightning strikes, and the importance of understanding temperature characteristics.

Re1：Thank you so much! Yes, the circuit breaker is important protection equipment in the power system, especially when there is a short circuit current, the circuit breaker can quickly open the current; The system failure caused by lightning is a common problem in power system. The circuit breaker plays an obvious role in cutting off the short-circuit current caused by lightning. (page 1, line26)

Q2：The research objectives could be explicitly stated to provide clarity on what the paper aims to achieve. Additionally, defining the scope of the study would help readers understand the limitations and applicability of the findings?

Re2：Thank you and sorry! Yes, the research goal of this paper is to clarify the temperature and speed of the gas flow, analyze the state of gas ionization, and provide a basis for the optimization of subsequent circuit breakers, especially in the optimization of electrode selection and arc interrupter optimization. (page 2, line68)

Q3：The utilization of the schlieren technique and image recognition technology is well-justified. However, more details about the experimental setup, conditions, and any potential limitations should be provided to ensure the reproducibility of the results.

Re3：Thank you so much! The schlieren equipment has an incident light part and a receiving light part, and the test circuit breaker has observation holes on both sides. The internal air pressure can withstand 5.0MPa. The glass adopts optical glass, which has high light transmittance and little influence on the schlieren test.  (page 6, line142)

Q4：The paper mentions obtaining temperature characteristics and airflow features, but the specifics of the data obtained and the methodology used for analysis are not clear.

Q5：The statement about the generation of shock waves and airflow characteristics is intriguing. A more detailed discussion on the implications of these findings for circuit breaker design, operation, and potential issues faced during lightning strikes would strengthen the paper.

Q6: Clarify how the shock wave velocity and airflow boundary diffusion velocity were measured. Additionally, providing context on how these characteristics relate to the circuit breaker's performance and potential breakdown would add depth to the analysis.

Q7:The inverse proportionality of temperature change to the square of time is an interesting finding. Elaborate on the significance of this relationship and discuss how it can be utilized in practical circuit breaker design or maintenance strategies.

Re7: Thanks for the expert advice! The change of temperature, especially the change of critical plasma temperature, will affect the development process of space arc and the change of electric field. The relationship between the change of plasma and time is obtained, which provides a basis for further optimizing the practice of circuit breaker opening and closing. (page 8, line 181)

 

Q8: The rapid decay of airflow boundary diffusion velocity is mentioned, but the implications of this decay on the circuit breaker's stability or susceptibility to further lightning strikes should be discussed.

Re8：Thanks to the advice of experts, the diffusion of high temperature gas, cooling and recombination of plasma will promote the medium to return to the state of insulation, which affects the impact of lightning through the process, the article has discussed and supplemented this part.

Q9: The concentration of maximum temperature between 6000 and 8000 K is noted. Provide insights into why this temperature range is critical and discuss its potential impact on the circuit breaker's material integrity.

Re9：Thanks to the question of the review experts, the temperature of 6000K-800K is the temperature at which SF6 forms stable plasma. The region and position of this gas will affect the change of the electric field, and its shape will also affect the change of the electric field on the electrode surface, which has a strong randomness to trigger impact penetration, and is also the part that affects the probability of rebreakdown. (page 8, line 183)

Q10: The conclusion should provide a concise summary of key findings and explicitly state how the results contribute to the design and optimization of circuit breakers. Additionally, suggest potential applications or future research directions based on the obtained insights.

Re10：Thanks to the valuable opinions of the experts, the author refined and modified the conclusion after discussion, combined with the content of the paper to add a conclusive description, at the same time, in view of the plasma temperature and velocity changes, put forward the optimization of electrode optimization, arc quenching chamber optimization and opening speed optimization ideas. (page 10, line 231)

 

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This manuscript was very informative and present format,  recommend to accept  for Publication and minor English correction requirements.

 

Comments on the Quality of English Language

Minor English revision was  required.

Author Response

Q: This manuscript was very informative and present format, recommend to accept  for Publication and minor English correction requirements.

R: Thanks to the valuable advice of the experts, the author has modified the grammar problems and spelling errors of the article according to the content of the article, so as to improve the readability of the article.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The review report of the paper can be found in the attached file.

Comments for author File: Comments.pdf

Author Response

Q1: The density of the electric charge is noted, as a rule, with ρ, and to show how the charge is distributed, the index v is added for the charge distributed in the volume, respectively s if the charge is distributed on the surface. The electric charge considered in equation (1) is distributed in volume, which is why I propose that it be denoted by ρv and not by Q. As a rule, Q denotes the entire electric charge, which density function is expressed with the relation,

R1: Thanks to the guidance of experts, yes, when considering the distribution of plasma in the article, it should be considered in accordance with the density distribution, which has been corrected in the article. (page 2, line 27)

Q2: Equations (1), ..., (10) are taken from the literature, they are not established by the authors, which is why it is necessary for the authors to specify the works from which they were taken. This is necessary to make it more clear what the scientific contributions of the authors are in this paper.

R2: Thanks to the advice of experts, in fact, for the model and test process in the paper, the author only considered the change of charge and the movement speed and change process of plasma, especially gas ions, so the variable of temperature T and speed v were added. The rest of the cited literature has been marked. (page 2, line 28)

Q3: The paper does not detail how the curves presented in figures 3, 4 and 5 were made. It is necessary that the paper be completed with details that clarify this issue.

R3: Thank you for the opinions of experts, this is the selection of fixed-point temperature in the simulation process, select a point of critical electric field near the electrode, you can obtain the temperature, speed and acceleration and other variables at this point, because the optimal design of the circuit breaker pays more attention to temperature, speed and conductivity, so the author selected the three variable processes in the article. (page 5, line 124)

Q4: The representation scale used in figure 5 for conductivity is not linear. The work does not specify anything in this regard. It is necessary for the authors to specify which representation scale they used for the conductivity in figure 5.

R4: The conductivity is still the process of parameter change with time. After the calculation is completed, the conductivity change with time at the electric field critical point near the electrode surface is obtained. (page 6, line138)

Q5: More details are needed on how figures 8, 9 and 10 were obtained. This is not apparent from the paper.

R5: Ok, thanks to the expert's opinion, FIG. 8 is a schlieren image of the development of high temperature air flow during the typical lightning current induced interelectrode breakdown process. In this paper, the motion velocity of air flow at any temperature can be obtained, and the change of gas conductivity can be analyzed. Figure 9 shows the change of high temperature air flow at the initial time of breakdown. According to the relationship between image gray level and temperature, a temperature analysis method is proposed. Figure 10 is the process of gray analysis of temperature. The paper gives the temperature distribution at 0.0002 moments. (page 7, line 171)

Q6: Figures 11 and 12 show the temperature and conductivity values as a function of time, but it is not specified how the respective values were obtained. It is necessary to specify the instruments used and their accuracy class for the measured values.

R6: The only two used in the article were a high-speed camera and a schlieren device; The analysis method used has two steps. One step is to calibrate with the ambient temperature, and calibrate with the flame temperature to obtain the relationship between temperature and gray level. The second step is to obtain the gray level distribution of the breakdown process, and carry out gray scale in different regions to obtain the corresponding temperature value.

 

Q7: I think it is necessary to compare the results from figure 5 with those from figure 12 and specify, in %, the difference between them in order to be able to state that the experimental results are close to the theoretical ones.

R7: Thank you!, Figure 12 is the statistical value of the region, and Figure 5 is the recorded value of a single point. Therefore, the statistical value in FIG. 12 is slightly smaller than that in FIG. 5 because the arc radius in SF6 is small, but the time from the beginning to the conductivity reduction is not much different, which accords with the calculation results.

 

Q8: How is it justified that the minimum conductivity value in figure 5 is 1, and in figure 12 the minimum value is approximately 10-19

R8: Thanks to the opinions of experts, the temperature of the simulation calculation point in FIG. 5 changes greatly with time, which belongs to the point temperature; FIG. 12 is the statistical temperature of the region, and the two are different. FIG. 5 is to show that the electric field at this point can no longer depend on the electrode size at this temperature. Figure 12 is to show that in this area, the gas temperature conductivity is large, and the circuit breaker should be optimized on the interrupter design or closing scheme.

Author Response File: Author Response.pdf