Detection of Self-Healing Discharge in Metallized Film Capacitors Using an Ultrasonic Method

Round 1

Reviewer 1 Report

In this manuscript, Ma and co-authors investigate on a method based on low frequency ultrasonic signals for the detection of self-healing discharge in capacitors made of metallized polypropylene film. The paper is well-organized offering considerable information.  Here are a few suggestions that need to be followed:

Pag. 3: It is not clear what the black object placed on the capacitor stands for. Does it represent the power supply of the capacitor? Where are the materials of the capacitor? It would seem from the figure that ultrasonic waves propagate inside a single material. You should update the figure caption in order to avoid confusion.

Pag. 4 lines 106-108: “The direct propagation path of ultrasonic waves…after traveling through direct path x1.” What about the reflected wave at the interface? Are you omitting it? Why? Comment in the text.

Pag.5 line 142: “… the discharges are received by an acoustic emission sensor with high sensitivity.” What kind of sensor did you use in your measurements? Is it a custom or commercial device? You should provide more information like of the sensor. Moreover, there are recent examples of ultrasonic sensors, which have the same working spectrum of the ultrasonic waves emitted in the investigated capacitors. What is the frequency band of the sensor you used for the measurements? What about the use of sensors with larger spectrum? Comment in the text. Here are the recent examples of ultrasonic sensors from the literature:

- Spiral-Shaped Biologically-Inspired Ultrasonic Sensor. Doi: 10.1109/TUFFC.2019.2948817

- Ultrasonic Transducers Shaped in Archimedean and Fibonacci Spiral: A Comparison. Doi: 10.3390/s20102800

Pag. 6 line 159: It should be ‘below’ instead of ‘bellow’.

Pag. 6 line 164: “… (600-700V)…”. From Fig. 8, the partial discharge starts at about 600V. Why are you giving a range from 600V to 700V? Did you make other measurements finding other results? Clarify this point in the text.

Pag. 7 line 182: It should be ‘Ignoring’ instead of ‘Ignore’.

Pag. 7 line 186: “Received ultrasonic partial discharges with different shapes…”. Why did you receive different signals? Are they undesired echoes?  

Pag. 10 line 241: “…Butterworth filter…”. You should provide information on the filter. Is it an active or passive circuit? Comment in the text.

Pag. 11 line 260: “…software package was developed.” Are there other attempts of software developing in the literature concerning your application? You should comment in the text.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Thanks for the interesting article, but there are some comments and questions that have to be answered before the publication.

Some minor comments.

Page 1, Line 41. It is better to specify - “sheet resistance of electrodes”

Page 2, Line 58. I think the description of MFC structure (Fig.1) should start with capacitor elements, not with “wire”. Rearrange the words order please.

Page 2, Line 67. 100 nm is an extremely high value for modern metallization thickness. The self-healing won’t be effective with this thickness of electrodes.

Page 3, Line 80-82. The films becomes punctured because of electric breakdown. The heat causes the evaporation of the electrodes.

Page 3, Line 83. Not “stored”, but “dissipated”.

Page 3, Line 87. “And the sound waves are mainly in the ultrasonic frequency band (40k-80kHz)” - Where is it coming from? Any references?

Page 5, Line 140-141. “A series of high voltages are applied to two of the TERMINALS of the tested capacitors by the adjustable DC power SUPPLY.”

Page 9. Line 232. n – is not an integer. SH investigators pointed to the range from 2.5 to 7 (including 4.7, etc., for example).

Page 10, Line 255. You mentioned the liquid media as a possible reason for peak frequencies difference. What type of capacitor are you testing? Is it dry-type or impregnated?   

 

Questions and major comments.

Page 6. Line 168-169. Of course, the capacities of tested capacitors are important (by the way, why don’t you call it reactive power?), but for better understanding you should clearly point to their capacitances, or even capacitances of inner capacitive elements. It is necessary for understating the value of voltage applied to each element. Try to use additional scheme with the values of capacitance and voltage drop at all capacitive elements between terminals under voltage.  

Page 9. Line 222. I can’t understand why you are taking the amplitude of the ultrasonic self-healing signal and use it in the equation for self-healing energy expression? It seems to be incorrect. What is the capacitance value in this case? Please give an example of Wsh calculation.

Page 11, Fig. 14. The explanation of the difference between the Y-N and delta connections spectra seems to be inconsistent. A deeper analysis is required here. In my opinion, the main difference between “Y-N” and “delta” structures is the interconnections of capacitive elements. What do you mean when point to inside film and liquid media?

Page 12, Line 278. You are saying that self-healing characteristics were revealed for three! typical MFCs, but in the article we see the comparison of 2 types? Can you explain this?

Did you test your software at AC voltage applied to the capacitor?

What is the purpose of counting SH events in your opinion?

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Thank you for the meticulous revision. Well done.  

Reviewer 2 Report

Thank you for the corrections.

It was really important to note the you got ultrasound energy of SH which is proportional (in some way) to original SH energy.

I/ll be waiting for you further work results.