Abstract of the thesis entitled – “Verification of Power System Protection Schemes using Temporal Logic Framework”
Protection systems are employed on power systems to save the networks from damages during faults.
Designs of power system protection schemes are validated today using Monte-Carlo simulation and manual interpretation of results. The limitation of such simulation based validation is uncertainty of complete coverage of all possible operating conditions due to the time complexity of simulation.
Recognizing the shortcomings of random testing, various automated design validation strategies to validate the correctness of a design efficiently under a large number of operating conditions of interest are becoming increasingly popular in the domain of CAD of VLSI circuits. Following these approaches, this research work attempts to develop an efficient automated technique for validating power system protection schemes using temporal logic assertions.
For this, behavioral models of the protective devices are devolved first. The hybrid automata models of the relays and circuit breakers represent the functionalities of the devices under different operating state. Desired properties of the protection system are then encoded in temporal logic and verified for the design models using assertion checker (Chapter 2).
A systematic method to discover the power system operating conditions for which the protection system may fail to response appropriately is proposed next in Chapter 3. It uses Swarm Intelligence for the same. A modified version of Particle Swarm Intelligence which is suitable for optimizing discontinuous objective functions has been developed. The proposed verification technique has been tested on several IEEE standard power systems and the performance of the method is compared with the conventional approach of verification (Monte-Carlo simulation). It is found that the proposed method is better than the existing approaches both in terms of accuracy and computational complexity. At the end of the chapter, a sensitivity analysis based approach is introduced that can be used to modify the relay parameters to avoid undesired trippings during operation
During heavy loading conditions, a distance relay may trip due to load encroachment. This was one of the root causes of the blackout happened in India. One of the common practices is to use a load blinder or an Anti-Encroachment-Zone in the operating characteristic of a distance relay to prevent it from unnecessary tripping due to load encroachment. However, this approach may make the relay insensitive to fault and the appropriate design of load blinder is a challenging task. Instead of blocking the relays in normal operating condition, one should rather operate a power system in such a way that the apparent impedances of the distance relays never enters into their operating zones when there is no fault in the network. These issues are addressed in Chapter 4.
List of Publications from the thesis
[1] A. Sengupta, S. Mukhopadhyay and A. K. Sinha, “Automated Verification of Power System Protection Schemes - Part I: Modelling and Specifications", IEEE Transactions on Power Delivery, Vol.
30, No. 5, pp. 2077 - 2086, 2015.
[2] A. Sengupta, S. Mukhopadhyay and A. K. Sinha, “Automated Verification of Power System Protection Schemes - Part II: Test Case Generation using Swarm Intelligence", IEEE Transactions on Power Delivery, Vol. 30, No. 5, pp. 2087 - 2095, 2015.