Time Synchronization Sensitivity in SV-based PMU Consistency Assessment
Round 1
Reviewer 1 Report
I believe that this paper provides a useful contribution. Dealing with edge-cases involving abnormal conditions is challenging, but important. This paper provides guidance for operators, as well as a method which can be automated within PMUs (in certain situations).
The paper appears to assume that the PMU (with digital inputs) has a high-performance clock with low drift, or that the PMU remains synchronized while the SAMU loses sync, which I’d suggest is a narrow use case. Essentially, the PMU is performing functionality like a Daneo device to monitor the coherence of SV streams. The algorithm applied appears to cater for the typical behaviour of clocks during resynchronization, which is a benefit.
Figure 5 should have a legend, as otherwise it is difficult to understand the meaning of the plots (it’s not immediately clear that there are two plots superimposed).
In Figure 6, there is a dip in TQ at about 70 s. It goes below the threshold, which suggests the algorithm isn’t completely stable. This is mentioned in the text, but the description is not clear – it’s not clear how the algorithm deals with this, and the corresponding corrected plot isn’t given.
Minor point: “IEC Std 61850” should just be “IEC 61850”.
Author Response
I believe that this paper provides a useful contribution. Dealing with edge-cases involving abnormal conditions is challenging, but important. This paper provides guidance for operators, as well as a method which can be automated within PMUs (in certain situations).
We thank the Reviewer for the positive comment.
The paper appears to assume that the PMU (with digital inputs) has a high-performance clock with low drift, or that the PMU remains synchronized while the SAMU loses sync, which I’d suggest is a narrow use case. Essentially, the PMU is performing functionality like a Daneo device to monitor the coherence of SV streams. The algorithm applied appears to cater for the typical behaviour of clocks during resynchronization, which is a benefit.
We do see the Reviewer's point. In a modern digital substation, it is reasonable to expect that all the IEDs are synchronized by a common time source (e.g., via PTP). However, in view of a broader inter-operability, this paper considers the case of redundant synchronization sources. Therefore, both SAMU and PMU have an independent time reference. In this case, it is possible to exploit this redundancy to minimize the time interval without reliable measurement results.
Figure 5 should have a legend, as otherwise it is difficult to understand the meaning of the plots (it’s not immediately clear that there are two plots superimposed).
We thank the Reviewer for the insightful comment that helped us to improve the readability of the graph. In the revised version of the manuscript, we included a legend to differentiate the two datasets.
In Figure 6, there is a dip in TQ at about 70 s. It goes below the threshold, which suggests the algorithm isn’t completely stable. This is mentioned in the text, but the description is not clear – it’s not clear how the algorithm deals with this, and the corresponding corrected plot isn’t given.
The Reviewer is absolutely right. We were aware of the imperfect stability of the proposed envelope extractor. Indeed, the proposed method is intended to work on-line and we prioritized its lightweight implementation, rather than its accuracy. Nonetheless, it is worth noticing that similar outliers are typical in time measurements with devices relying on different clocks, but are sparsely distributed and do not follow pre-defined trends. For this reason, we prefer to perform an extra-check (i.e. to wait five iterations) before claiming a time quality change. In the text, the paragraph describing how the algorithm deals with this has been modified and extended for the sake of clarity.
Minor point: “IEC Std 61850” should just be “IEC 61850”.
Well noted! Thank you for the careful reading. The manuscript has been thoroughly proofread in order to remove possible typos or grammar inconsistencies.
Reviewer 2 Report
The topic of article is very relevant at the present time. The many digital substations are in use today. It's necessary to synchronize measurements in time. This task is difficult if the GPS isn't available. The authors consider the problem of data synchroniation in time.
Author Response
The topic of article is very relevant at the present time. The many digital substations are in use today. It's necessary to synchronize measurements in time. This task is difficult if the GPS isn't available. The authors consider the problem of data synchroniation in time.
We thank the Reviewer for her/his positive comment. Much appreciated.
Reviewer 3 Report
The article is interesting and is devoted to the actual topic.
Notes:
1. It is necessary to present the mathematical model used in the study.
2. Clearly formulate scientific novelty.
3. Refine the abstract. Need to write more clearly
Author Response
Dear Reviewer, please see the response in the attachment.
Author Response File: 
Author Response.pdf
Reviewer 4 Report
1. The abstract section should be more intensively focused on the main idea directly and must contain the contribution of this manuscript with numerical result indicators.
2. A more state-of-the-art literature review should be undertaken to cover various applications of the proposed approach.
3. More explication of the time quality evaluation.
4. Please have an introductory paragraph on the results and discussion.
5. More discussion for simulation results.
6. Add new references to recent ones.
Author Response
- The abstract section should be more intensively focused on the main idea directly and must contain the contribution of this manuscript with numerical result indicators.
We thank the Reviewer for the suggestion. We revised the abstract in order to be more corresponding to the actual contribution of the paper. To this end, we also included a brief summary of the main quantitative results as obtained in the numerical and experimental tests.
- A more state-of-the-art literature review should be undertaken to cover various applications of the proposed approach.
We thank the Reviewer for the suggestion. In the revised manuscript, we included new references to recent contributions in the field of IEC 61850 measurement applications. Furthermore, we better explain which could be the possible benefits of the proposed approach in real-world installations.
- More explication of the time quality evaluation.
We thank the Reviewer for the suggestion. In the revised manuscript, we better explain the importance of an exact knowledge of the time quality, with specific reference to phasor measurements.
- Please have an introductory paragraph on the results and discussion.
We thank the Reviewer for the suggestion. We revised the text accordingly.
- More discussion for simulation results.
We thank the Reviewer for pointing out an aspect that could have been not properly addressed in the previous version of the manuscript. We better clarified the simulation objectives and we better discussed the simulation results.
- Add new references to recent ones.
We thank the Reviewer for the suggestion. In the revised manuscript, we included new references to recent contributions in the field of IEC 61850 measurement applications.
Round 2
Reviewer 3 Report
Accept in present form
