Simulation of a Line Voltage Regulator in a Low-Voltage Grid That Is Subject to Strong Voltage Surges Due to the Provision of Fast Frequency Reserve
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
1. Clarity of Research Methodology
o Elaborate on the working mechanism of Line Voltage Regulators (LVR) and their specific implementation in the simulation. While the article mentions the basic principles of LVRs and uses a product from Hitachi Energy, further details on how exactly LVRs adjust the voltage (e.g., steps involved in voltage regulation, delay times, etc.) are crucial for understanding the assumptions and limitations of the model.
o Specify the assumptions made in the model. The paper should explain in more detail the assumptions made for the simulation study, such as the basis for the 5-second delay in LVR adjustment, and how these assumptions could impact the study's outcomes.
2. Depth and Breadth of Results
o Conduct a comparative analysis of results under different conditions. It is recommended to add comparative analyses for different LVR positions and load conditions to show how the LVR position affects voltage regulation effectiveness and the probability of voltage overruns under various conditions.
o Consider the complexity of real power grids. The operational conditions of real power grids are much more complex than the model described, including changes in grid topology, randomness of different types of loads, etc. Discussing how these factors might affect the study's results or considering them in future research is advisable.
3. Practicality and Applicability
o Provide specific suggestions on LVR operation modes. The article suggests adjusting the operation mode of LVRs through communication with aggregators. Further exploration of how this communication mechanism could be implemented and its specific impact on grid operators is recommended.
o Discuss the applicability to different grids. The optimal position of an LVR depends on the voltage distribution along a specific line; hence, discussing how the study's findings could apply to other types or sizes of grids or proposing a methodology to help operators assess the best deployment locations for LVRs in their networks is suggested.
4. Literature Review
o Strengthen the connection with existing research. In the introduction or literature review section, a more comprehensive review of prior research in the field, especially recent developments regarding the use of LVRs, FFR strategies, and grid voltage regulation, should be conducted to place the contributions of this study within a broader research context.
5. Conclusions
o Offer more specific recommendations. Although several suggestions are made, these recommendations should be more specific, such as how to improve LVR adjustment strategies or optimize LVR layouts to enhance overall grid performance.
o Discussion on future research directions. The conclusions should include clear recommendations for future research directions, such as exploring more advanced voltage regulation technologies or developing simulation models that can accommodate more complex grid conditions.
6. Visualization and Data Presentation
Improve the readability of charts and data. Ensure all charts are clear, understandable, and all data are thoroughly explained and annotated. Consider adding visual aids, such as diagrams or flowcharts, to help readers better understand the workings of LVRs and the simulation process.
7. Article title
In the article title, it is recommended not to abbreviate proprietary terms. This ensures clarity and accessibility for readers who may not be familiar with specific acronyms or abbreviations.
Author Response
- Clarity of Research Methodology
o Elaborate on the working mechanism of Line Voltage Regulators (LVR) and their specific implementation in the simulation. While the article mentions the basic principles of LVRs and uses a product from Hitachi Energy, further details on how exactly LVRs adjust the voltage (e.g., steps involved in voltage regulation, delay times, etc.) are crucial for understanding the assumptions and limitations of the model.
Please find the requested information on page 3 and 4. A chapter has been introduced to further explain the working mechanism of the LVR and its implementation in the simulation.
o Specify the assumptions made in the model. The paper should explain in more detail the assumptions made for the simulation study, such as the basis for the 5-second delay in LVR adjustment, and how these assumptions could impact the study's outcomes.
The main assumptions are specified on page 4. Here is an excerpt about the basis for the 5 second delay: “We have set the delay to 5 seconds, as we assume that this corresponds to the current control setting of the LVR used by Sundsvall elnät. Furthermore, we assumed the delay to be adjustable in some interval. A comparative study from 2014 shows that time delays of tenths of a second to a few minutes can be set for the control algorithms of established tap changers [9]. In general, a shorter delay is expected to result in more precise control and fewer voltage maintenance problems. However, we considered a delay shorter than 5 seconds to be unlikely, as this could lead to a more sensitive reaction of the LVR to short-term voltage fluctuations. The resulting more frequent voltage adjustments would lead to higher wear and tear.”
- Depth and Breadth of Results
o Conduct a comparative analysis of results under different conditions. It is recommended to add comparative analyses for different LVR positions and load conditions to show how the LVR position affects voltage regulation effectiveness and the probability of voltage overruns under various conditions.
The results chapter was revised, and a section was added in which the scenarios are all compared. Please find the comparative analysis on pages 20 and 21.
o Consider the complexity of real power grids. The operational conditions of real power grids are much more complex than the model described, including changes in grid topology, randomness of different types of loads, etc. Discussing how these factors might affect the study's results or considering them in future research is advisable.
A discussion chapter has been introduced on page 20 in which this comment is addressed as follows: “It should be noted, however, that although the simulation provides qualitatively plausible results, it is unlikely to exactly match the voltages that would occur in reality. To do justice to the complexity of real power grids, further factors would have to be taken into account. This includes the consideration of uneven loading of the 3 phases, which was neglected in this work.”
- Practicality and Applicability
o Provide specific suggestions on LVR operation modes. The article suggests adjusting the operation mode of LVRs through communication with aggregators. Further exploration of how this communication mechanism could be implemented and its specific impact on grid operators is recommended.
The corresponding modification can be found in the discussion chapter on page 20: “A specific implementation proposal could be as follows: The aggregator sends the network operator an updated list containing information about the customers on standby for FFR delivery, their offered power, and trigger frequency. With this infor-mation, the grid operator can anticipate how much the voltage of the affected line would increase upon FFR activation. The network operator monitors the grid fre-quency and adjusts the LVR setting when the FFR reserve trigger frequency is reached. In this specific case, this could involve bypassing the LVR or manually adjusting the tap change to 0% voltage change, as the grid can handle the activation without the LVR.”
o Discuss the applicability to different grids. The optimal position of an LVR depends on the voltage distribution along a specific line; hence, discussing how the study's findings could apply to other types or sizes of grids or proposing a methodology to help operators assess the best deployment locations for LVRs in their networks is suggested.
This comment is discussed on page 20: “Therefore, the optimal installation location is probably somewhere in first third of the line. However, this must not be true for other grids since the optimal installation location depends on the course of the voltage along the affected line. Grid operators are therefore advised to take voltage measurements at various locations on a line affected by voltage fluctuations. For the installation of the LVR, a position should be selected that is as close as possible to the end of the line, but where there are no significant deviations from the reference voltage. If no or not enough voltage measurement points are available, the simulation created can be used to roughly estimate the voltage curve along the affected line. The grid structure, feed-in and consumption data, fuse variables and line impedances are required as input for this.”
- Literature Review
o Strengthen the connection with existing research. In the introduction or literature review section, a more comprehensive review of prior research in the field, especially recent developments regarding the use of LVRs, FFR strategies, and grid voltage regulation, should be conducted to place the contributions of this study within a broader research context.
To strengthen the link to existing research, the article now also refers to the following sources:
- Gomez-Gonzalez, M.; Hernandez, J.C.; Vera, D.; Jurado, F. Optimal sizing and power schedule in PV household-prosumers for improving PV self-consumption and providing frequency containment reserve. Energy 2020, 191, 116554 [CrossRef]
- Holt, M.; Maasmann, J.; Rehtanz, C. Line voltage regulator based on magnetic controlled inductors for low-voltage grids. 24th International Conference & Exhibition on Electricity Distribution (CIRED) 2017, 278-281 [CrossRef]
- Holt, M.; Rehtanz, C. Optimizing line-voltage-regulators with regard to power quality. Electric Power Systems Research 2021, 190, 106654 [CrossRef]
- Hartung, M.; Baerthlein, E.; Panosyan, A. Comparative study of tap changer control algorithms for distribution networks with high penetration of renewables. CIRED Workshop - Rome 2014, Paper 0376, 1-5 [CrossRef]
- Conclusions
o Offer more specific recommendations. Although several suggestions are made, these recommendations should be more specific, such as how to improve LVR adjustment strategies or optimize LVR layouts to enhance overall grid performance.
The Conclusions on pages 21 and 22 has been supplemented with recommendations regarding the improvement of the LVR layouts:
“A comparison of the positions of the LVRs considered has shown that both vari-ants have weak points. In some cases, an LVR located at the beginning of the line cannot prevent as many overvoltages at the end of the line as an LVR positioned fur-ther back. However, if the LVR is too close to the end of the line, voltage deviations can occur upstream of the LVR, which can therefore no longer be controlled. To identify the best location for the LVR, network operators are recommended to carry out voltage measurements along the affected line and select the location taking the following two criteria into account:
• The installation location of the LVR should not be behind a node where voltage deviations are already occurring.
• In compliance with the first criterion, the distance between the LVR and the end of the line should be minimized.”
o Discussion on future research directions. The conclusions should include clear recommendations for future research directions, such as exploring more advanced voltage regulation technologies or developing simulation models that can accommodate more complex grid conditions.
The Conclusions on pages 21 and 22 has been supplemented with recommendations for further possible research directions:
“For a more precise calculation of the voltage profile of the affected line, the simulation must better reflect the complexity of real low-voltage grids. In order to improve the simulation, the implementation of the following aspects is recommended, for example as part of subsequent work:
• Consideration of the asymmetric phase feeding and loading by the prosumers connected to the grid.
• Consideration of local changes in radiation intensity due to cloud cover, taking into account the grid topography.”
- Visualization and Data Presentation
Improve the readability of charts and data. Ensure all charts are clear, understandable, and all data are thoroughly explained and annotated. Consider adding visual aids, such as diagrams or flowcharts, to help readers better understand the workings of LVRs and the simulation process.
The layout of all tables and charts has been adapted to the specifications. A graphic of the scheme of the LVR has been added to better illustrate its structure and function. Please find it on page 3. Also, new tables were created to enable better comparability between the scenarios in the results chapter.
- Article title
In the article title, it is recommended not to abbreviate proprietary terms. This ensures clarity and accessibility for readers who may not be familiar with specific acronyms or abbreviations.
The article title has been revised and the abbreviation "FFR", to which the commentary presumably refers, has been written out in full. The title of the article now reads: Simulation of a Line Voltage Regulator in a low-voltage grid that is subject to strong voltage fluctuations due to the provision of Fast Frequency Reserve
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Authors,
1) In the Intoduction of this paper, descriptions and references to various studies in related research fields are lacking.
2) A summary of the organization of this paper is missing in the last sentence of the Introduction section.
3) Chapter 3 is understood to explain the simulation process to verify the effectiveness of the LVR proposed in this paper. The title of Chapter 3 should be changed accordingly. In other words, in order to verify the LVR effect, it seems necessary to emphasize the simulation verification procedure proposed in this paper.
4) Chapters 4 and 5 cover simulation conditions and results. Grouping these and dividing them into subcategories will help to explain the content of the paper. e.g.) 4.1, 4.2
Best regards,
Reviewer
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors-
Citation Formatting: Make sure the citation style is consistent and complete throughout the document. For example, the references to sources within the text should follow the same style, whether using brackets [1] or parentheses (1). Additionally, the full reference list at the end should be formatted uniformly, adhering to a standard citation style such as APA, IEEE, or the journal's preferred style.
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Methodology Specificity:The methodology section is detailed but might benefit from a more step-by-step breakdown of the simulation process. For instance, including a flowchart summarizing the simulation steps would enhance understanding. Lines 96-134 (Functioning of the LVR)
- Conclusion Enhancement:The results are well presented, but interpreting the significance of the findings in more practical terms could be beneficial. For example, discussing how these results could impact grid operators' strategies would add practical value.
Author Response
Citation Formatting: Make sure the citation style is consistent and complete throughout the document. For example, the references to sources within the text should follow the same style, whether using brackets [1] or parentheses (1). Additionally, the full reference list at the end should be formatted uniformly, adhering to a standard citation style such as APA, IEEE, or the journal's preferred style.
Brackets [1] are used uniformly for citation. The reference list is formatted uniformly. The formatting corresponds to the citation style specified by the journal (see file sensors-template.dot).
Methodology Specificity: The methodology section is detailed but might benefit from a more step-by-step breakdown of the simulation process. For instance, including a flowchart summarizing the simulation steps would enhance understanding. Lines 96-134 (Functioning of the LVR)
As suggested, a flowchart diagram has been added that summarizes how the LVR works (see Figure 3 on page 5).
Conclusion Enhancement:The results are well presented, but interpreting the significance of the findings in more practical terms could be beneficial. For example, discussing how these results could impact grid operators' strategies would add practical value.
The conclusions already contain measures that have a direct impact on the grid operator's strategy. These include communication with the aggregator and the follow-up steps to be taken to prevent the problems described. This is discussed on page 21 (including a specific implementation proposal) and summarized on page 23.
Reviewer 2 Report
Comments and Suggestions for AuthorsDear Author,
This revised paper has been carefully reviewed, and the results of the review are as follows.
1) ‘7. Discussion’ should be corrected to ‘6. Discussion’ on page 20.
2) '6. Discussion' above should be included in the simulation results section of chapter 5.
Best regards,
Reviewer
Author Response
This revised paper has been carefully reviewed, and the results of the review are as follows.
1) ‘7. Discussion’ should be corrected to ‘6. Discussion’ on page 20.
2) '6. Discussion' above should be included in the simulation results section of chapter 5.
As suggested, the simulation results and the discussion chapter were combined into one chapter and numbered correctly
