final PM Revised Presentation of islanding detection of grid connected (2).pptx

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1. Islanding Detection of a Grid-connected DFIG-based Wind Generator SUBMITTED BY PRANENDU MANNA ENROLLMENT NO- 181001939002 UNDER THE GUIDANCE OF Dr. Tanaya Datta Das, Assistant Professor, ELECTRICAL ENGINEERING DEPARTMENT

2. CONTENTS ABSTRACT INTRODUCTION OBJECTIVES LITERATURE REVIEW CONVENTIONAL ROCOF RELAY ACTIVE POWER PERTURBATION EFFECT OF ISLANDING CASE OF SWITCHING CONCLUSION REFERENCES

3. ABSTRACT Unintentional islanding may occur at any instance of time due to some faults or some anonymous problem in the system. It is a big problem for power system security, which can damage the equipment and also can be very dangerous for the maintenance workers. Therefore, fast detection of islanding is essential. In this paper, a hybrid Islanding Detection Relay (IDR) employing a scaled active power perturbation along with classical ROCOF based detection has been introduced. Active disturbance serves as an identifying factor in detection of an island. But keeping in mind the issue with the power quality, in this paper, it is administrated only on detecting a case of disturbance. A fuzzy estimator predicts the natural peak value of the ROCOF on detecting a disturbance. The magnitude of active power perturbation to be administered is scaled using this estimate such that it is introduced only in cases which fall in the Non-Detection Zone (NDZ) of the classical ROCOF based IDR. The results presented in the study illustrate the effectiveness of the proposed islanding detection scheme.

4. INTRODUCTION Islanding is the situation in which a distribution system becomes electrically isolated from the remainder of the power system, yet continues to be energized by DG connected to it. Traditionally, a distribution system doesn’t have any active power generating source in it and it doesn’t get power in case of a fault in transmission line upstream but with DG, this presumption is no longer valid. Current practice is that almost all utilities require DG to be disconnected from the grid as soon as possible in case of islanding. IEEE 929-1988 standard requires the disconnection of DG once it is islanded. Islanding can be intentional or Non intentional. During maintenance service on the utility grid, the shut down of the utility grid may cause islanding of generators. As the loss of the grid is voluntary the islanding is known. Nonintentional islanding, caused by accidental shut down of the grid is of more interest. As there are various issues with unintentional islanding. IEEE 1547-2003 standard 10 stipulates a maximum delay of 2 seconds for detection of an unintentional island and all DGs ceasing to energize the distribution system.

5. OBJECTIVES The objective of this work is To modify the classical ROCOF based IDR using an active power disturbance to achieve detection in cases which normally fall in the NDZ of the classical IDR. To introduce an active perturbation to achieve detection in cases of islanding such that the proposed method will lead to detection only in cases of islanding due to the absence of grid. It will distinguish between cases of islanding and switching. To minimise the magnitude of perturbation required for detection as per the operating condition without increasing the THD for switching cases.

6. LITERATURE REVIEW IdMs are generally classified into two main groups: (a) local schemes and (b) remote schemes. Local schemes are further classified into active and passive schemes. Active schemes are generally based on the concept of perturb and observe technique. Active and passive methods have some negative and positive aspects. Passive methods do not have any impact on power system; however, they have a large NDZ. Active methods are typically accurate, but they have undesirable impact on system’s power quality. When these two methods come together, it is not only possible to receive benefit from their advantages; it is possible to overcome their undesirable features also.

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12. CONVENTIONAL ROCOF RELAY Intentional frequency perturbation by recently researched active islanding detection techniques for inverter based distributed generation (DG) define new threshold settings for the frequency relays. This innovation has enabled the modern frequency relays to operate inside the non-detection zone (NDZ) of the conventional frequency relays. However, the effect of such perturbation on the performance of the rate of change of frequency (ROCOF) relays has not been researched so far. This paper evaluates the performance of ROCOF relays under such perturbations for an inverter interfaced DG and proposes an algorithm along with the new threshold settings to enable it work under the NDZ. The proposed algorithm is able to differentiate between an islanding and a non-islanding event. The general diagram of a conventional ROCOF relay is shown in the Fig. 1 .

13. Fig.- 1. General diagram of A conventional ROCOF relay

14. ACTIVE POWER PERTURBATION The RSC of the DFIG is normally regulated to run the DFIG at a maximum power received from the wind turbine (d-axis reference: 𝐾𝑜𝑝𝑡𝜔𝑟 2 ) and generate specified reactive power [10]. Ideally, the proportional and integral constant of the current loop PI control is selected in such a manner that the closed-loop response is as defined in equation no. (2) where 𝜏 refers to the closed-loop time constant. The drawbacks of the conventional ROCOF relay can be overcome by using a modified ROCOF based Islanding Detection Relay (IDR) by introducing a torque perturbation ( ∆𝑇𝑒 ∗ ) as discussed in [7]. However, the equation of the closed-loop transfer function given by (Fig. 2) is valid only when the switching and sampling delay as stated are neglected.

15. Fig.- 2. Block diagram of d-axis controller of RSC

16. Fig. – 3. Flowchart of modified ROCOF based IDR

17. CASE OF SWITCHING VS ISLANDING In this section, the ability of proposed IDR to distinguish between an island formation and switching events is discussed. The upper threshold value 𝛽2 should be high enough so that the generated ROCOF by any switching event is less than it The ROCOF is modified due to the presence of the perturbation injected by the proposed IDR for 100 ms after the detection of the disturbance. However, the peak values observed is seen to be much less than the upper threshold. Thus, simulations carried out show that the value of ROCOF observed for switching events does not exceed the threshold limit even after the system is perturbed. Both the proposed and conventional IDR are not affected by the switching event due to high value of the threshold 𝛽2.

18. CONCLUSION Islanding detection with active perturbation of variable magnitude based on the predicted natural peak value of ROCOF is proposed. In the proposed IDR, the perturbation required to produce detection is not administered during every disturbance. It will detect cases of islanding which normally are in the NDZ of classical ROCOF relay by injecting this perturbation. The objectives of the thesis can be achieved by using a fuzzy estimator to predict the peak 𝑅𝑂𝐶𝑂𝐹 which will be used to modify the magnitude of perturbation. This modification will be necessary for cases of islanding which normally occur in the NDZ of the classical ROCOF based relay. This will be the next work of this project.

19. REFERENCES [1] "IEEE standard for interconnecting distributed resources into Electric Power System," IEEE standard 1547 TM, 2019. [2] D. Salles, W. Freitas, J. Vieira and B. Venkatesh, "A Practical Method for Non-detection Zone Estimation of Passive Anti-islanding Schemes Applied to Synchronous Distributed Generators," IEEE Transactions on Power Delivery, vol. 30, pp. 2066-2076, 2015. [3] W. Freitas, W. Xu, C. Affonso and Z. Huang, "Comparative analysis between ROCOF and vector surge relays for distributed generation applications," IEEE Transactions on Power delivery, vol. 20, pp. 1315-1324, 2005. [4] T. Datta, A. K. Sinha and P. Bajpai, "Analysis of modified ROCOF relays for islanding detection of distribution systems with DFIG," 21st Century Energy Needs - Materials, Systems and Applications(ICTFCEN), pp. 1-6, 2016. [5] B. Liu and D. Thomas, "New islanding detection method for DFIG wind turbines," in 4th International Conference on Electric Utility Deregulation and Restructuring and Power Technologies (DRPT), 2011.

20. To Be Continued…….. [6] K. Jia, T. Bi, B. Liu, D. Thomas and A. Goodman, "Advanced islanding detection utilized in distribution systems with DFIG,“ Electrical Power and Energy Systems, vol. 63, pp. 113-123, 2014. [7] P. Gupta, R. S. Bhatia and D. K. Jain, "Active ROCOF Relay for Islanding Detection," IEEE Transactions on Power Delivery, vol. 32, no. 1, pp. 420-429, 2017. [8] O. Raipala , A. Makinen , S. Repo and P. Jarventausta , "An Anti-islanding Protection Method Based on Reactive Power Injection and ROCOF," IEEE Transactions on Power Delivery , vol. 32, no. 1, pp. 401-410, 2017. [9] T. Datta, P. Bajpai and B. R. Naidu, "Active Perturbation Based Islanding Detection Scheme for Grid Connected Wind Energy System," in 2018 IEEE Innovative Smart Grid Technologies - Asia (ISGT Asia) , Singapore, 2018. [10] C. F. Ten and P. A. Crossley, "Evaluation of Rocof Relay Performances on Network with Distributed Generation," in Developments in Power System Protection ,2008. IET 9th International Conference , 2020.