Research on the Distribution Characteristics of Transformer Axial Vibration under Short-Circuit Conditions Considering Damping Parameters

Round 1

Reviewer 1 Report

Paper: Research on the Distribution Characteristics of Transformer Axial Vibration Under Short-circuit Conditions Considering Damping Parameters

Comments:

1.  The structure of the paper is adequate. However, in the introduction section, it is recommended to avoid lumped references. The main contribution of each one must be clearly stated.

2. The mathematical formulation is correct. Nevertheless, It is recommended to include a complete nomenclature list with all the mathematical symbols and also main acronyms. Revise the journal rules on this aspect.

3. At the end of the conclusions it is recommended to state about two or three future works.

4. Size of figures and tables can cover all the pages wide to make them more readable.

5. Numerical validation of the authors' proposal is excellent. It allows identifying the main contributions in this research. Good job.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

This paper investigates the effect of short circuit conditions on the transformer axial vibration. The topic is interesting and of significant importance to the community. I have the following comments/suggestions for the revised version of the manuscript.

1. The introduction section contains very long sentences such as L59-64. It is difficult to extract the actual meaning from these sentences.

2. The references needs to be revised with some latest work cited.

3. The authors need to clarify and explain how equation 8 is obtained from equation 7. It seems many steps have been skipped which make it difficult for readers to understand.

4. The paper is focused on short circuit conditions but it would be interesting if the authors can comment on the effect of overcurrent (overload and not short circuit) on the transformer axial vibration.

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

The paper, according to the title and  abstract, concerns an issue of a transformer axial vibrations due to short-circuit with taking into account damping properties of the system. While the general idea behind the paper is clear, its presentation and a potential novelty  is vague. Sections 1 to 3.3 are mostly understandable. They describe preparation of a theoretical model based on mass-on-spring concept and also, partially, the system behaviour based on the model response in the form of vibration shapes for different load frequencies. This part does not introduce any new methods or tools, but can be regarded as a necessary part to properly present the used model. The subsection 3.4, where, probably, the most important part of the paper is located, is quite short and pose a difficulty for a reader to comprehend what and how was done there. This part misses some explanations that would allow to better understand the presented work.

Putting aside above issues, which can be always improved and/or explained through Authors response, more important is the aspect of novelty in the paper. Similar models, based on a mass-on-spring concept, which also contain damping factors, can be found in the literature (e.g. doi 10.1109/PESS.2000.867371). Some model based on the finite element method (FEM) also includes damping (e.g. doi 10.1049/iet-gtd.2018.5688). Therefore it seems that the model itself or introducing damping in general is something already known in the field. Performing calculations for short-circuit conditions also often appears in other papers. Therefore, a question arises: what is the contribution of this paper to the field of an electric transformer vibrations?

What is more, the part of the paper (sec. 3.4) regarding vibrations in the short-circuit conditions is very limited. Reader can expect this part of the paper to be more extensive.  For example, an analysis can be expanded in regard to damping properties possible influence in a given range or maybe comparison with more sophisticated FEM models. If Authors emphasize importance of damping, it would be proper to compare results for different damping properties values or even case when damping is omitted, to further stress the point that accounting of damping is really important. Currently, no physical values connected with damping are present in the paper. Equation (14) presents general relation, but no value of alpha or beta (or an explanation why they take used values) is given.

In conclusion,  I do not recommend publication of this paper in the current form.

General remarks:

·         Regarding title “Research on the Distribution Characteristics of Transformer Axial Vibration Under Short-circuit Conditions Considering Damping Parameters’’, based on what is a common practice in the mechanical field, instead of the term distribution, the word shape (as in mode shape) or, maybe, displacement distribution, could be more appropriate. Single word distribution is more often associated with probability  like probability distribution.

·         Equations (11) and (12) – there are three types of windings according to Fig. 2. How equivalent parameters (k_n or m_n)  for the single layer (that includes all three types of windings) from Fig. 1 are calculated? Also, what were assumed values of k_b and k_t?

·         Equation (14) – even though damping seems to be an important part of the paper, there is no indication of what values of damping properties were assumed in calculations.

·         Line 191 – How they are arranged in descending order? The following modes has increasing natural frequency. Please explain.

·         Line 192 – second part of the sentence: and change with the change of the square root … is quite obvious after recalling earlier the well known equation ω=(k/m)^0.5

·         Lines 211-212 seem out of place. If it is not a typo, please elaborate.

·         Lines 216-217 – What does it mean that ’’zero nodes increase’’? It concerns nodes where displacement remains zero during vibration? How they ‘’increase’’? Maybe their ‘’amount’’ or ‘’number of them’’ increases.

·         Lines 261-263 – I suppose 50Hz is a normal frequency in a standard operation. Please explain how the increased, 100 Hz, frequency is connected with the event of a short-circuit. Also, please clearly explain what is the difference between Fig. 7 and a single slice (for 100Hz) of 3D plot in Fig. 5b.

·         Line 273 – why this specific time t=2s appears when steady vibration conditions are being considered?

·         Line 276 – why radial displacement are being referenced to when the investigated model has degrees of freedom only in the one (axial) direction?

·         Line 321 – while frequency sweep results can be found in Fig. 5 and 6, how they can be used to verify the model?

·         Section 3.4 – including only single case in the analysis makes this section very modest. Expanding analysis through introducing variation of, for example, damping parameters, would help to formulate more general conclusions.

Language and editorial remarks

·         line 14 – the accurate restoration – ‘’restoration’’ does not seem to be right word here

·         line 29 – it is a bad practice to start a sentence with a number

·         lines 54-56 – second part, starting from but could not … till the end is unclear, please paraphrase or clarify.

·         Equation (1), last line – should not it be –k_bx_n instead of –k_nx_n ?

·         Table 1 – table is difficult to read because of the lack of distinction of units. They should be presented in square parentheses, e.g. [g/cm3], maybe even an extra column (with units) could added to the table. Also capital letters H, M and L appearing in, i.a. axial height of conductor are not explained. They possibly mean High, Medium and Low (voltage), but this should be written. Maybe they should be placed as a lower index for better readability?

·         Figure 3 – horizontal axis name is unclear. It concerns degree of freedom associated with specific disk? Or it is simply ‘’order of natural frequency’’? Legend in the plot is unnecessary.

·         Line 201 – should not it be reference to Fig. 4 (instead of 3)?

·         Lines 258-260 – this fragment is repeated on the next page

 

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 3 Report

Reception of the paper has improved after the revision. Authors response was extensive and explained  some of the questions listed in the first review. However, I would like to ask Authors for a further clarification on the below issues (using numbering from Authors response). All references are taken from the revised version of the paper.

Regarding comment/response no. 5

According to eq. (13) and Tab. 2, there will be three different stiffnesses “k”: one for each low, medium and high voltage windings, while between discrete masses (Fig. 1) there is assumed only one stiffness. What is the relation between them? Those three ‘’springs’’ would be in parallel? Maybe some drawing would help explain this?

What is more, in the line 202 there is suggestion that windings types (L, M, H) were modelled separately as presented frequencies in Fig. 3 concern only “high voltage winding”. How values only for one type of winding were obtained using lumped mass model?

Regarding comment/response no. 9

Now it is clear from where the value t=0.2s comes from. However, the statement (lines 223-224) seems odd in this place and would be better to incorporate it into next paragraph. For example: Figure 5 shows winding displacement changes in steady-state condition (t=0.2s) at 0-250Hz.

Regarding comment/response no. 7 and 21

As I understand from the response no. 21, horizontal axis in Fig. 3 contains simply order of the natural frequency (from 1 to 34). Therefore why the name “Disk” and not, for example, natural frequency order?

Perhaps I am missing something, but as the value of a natural frequency order (1th order=1, 2th=2 ..34th=34) in the horizontal axis is increasing, therefore frequency in the vertical axis is also increasing, how (line 203) frequencies “are arranged in descending order”? Please explain.

Regarding comment/response no. 14

If model has yet to be verified, then statement in line 341 is  not true. Also, using word “verification” in the name of section 3.3 (line 222) is not justified.

Regarding comment/response no. 20

Usually units are placed in square brackets. Currently they are only present in the first row. Also in the third column there is symbol rho which should be in the first column. When there is no unit (e.g. number of turns), it can be written as [-]. In the row “Total length of medium voltage winding” unit is missing.

Line 209 - equation number has not been updated after revision

Line 125, 126 – parameter ‘p’ is written in both lowercase (line 125) and uppercase (line 126) letter

Author Response

Please see the attachment.

Author Response File: Author Response.pdf