PhD Thesis Final Defense to be held on March 20, 2020, at 11:00

Photo Credit: Vasileios Papaspiliotopoulos

The examination is open to anyone who wishes to attend (Multimedia Room, Central Library of NTUA).

Thesis Title: Optimisation of Overcurrent Element Settings in Adaptive or Non-Adaptive Protection Systems of Modern Distribution Networks and Transmission Systems

Abstract: This PhD dissertation is concerned with the development of novel methods, regarding the concept of adaptive protection systems in modern distribution networks and the automated calculation of optimal relay setting values for the overcurrent elements of adaptive or non-adaptive protection systems. The latter method is appropriate for distribution networks, where overcurrent elements are applied as primary protection, as well as for transmission systems, where overcurrent elements serve as backup to the main protection.

As a first step, the fundamental principles of power system protection and the new features of modern protection techniques are described. Moreover, the theory of fault analysis is explained concisely, providing the essential background for the comprehension of short-circuit current nature and protection techniques. Great emphasis is laid on the special case of double-phase-to-ground faults in effectively grounded power delivery networks, involving fault resistance. It is demonstrated that the presence of fault resistance can result in more severe faults than the bolted ones.

Subsequently, a thorough literature review is conducted, regarding the protection issues arisen in modern distribution networks, owing to the presence of dispersed generation. The potential protection issues are investigated extensively, based on the technology, capacity and location of dispersed generating units. A representative part of the Hellenic distribution network is studied, which is characterised by high penetration of renewables, verifying the possibility of protection gaps. A complete protection solution based on modern techniques is proposed, which addresses the potential protection problems in active distribution networks, improving the traditional protection scheme of passive distribution networks.

Adaptive protection systems have gained increasing interest in the last decade. Several pilot projects have been materialised, leveraging the superior performance of this solution. In this context, an adaptive protection testbed is developed, which simulates the examined distribution network, by means of a real-time digital simulator, supervises the network topology and connection status of dispersed generating units, with the use of a central controller, and adjusts automatically the setting values of employed protection relays, in case of a considerable change in network operation. The functionality of the proposed testbed is demonstrated through a series of hardware-in-the-loop tests, using off-the-shelf control and protection devices.

Finally, the engineering problem of calculating optimal setting values for the utilised overcurrent functions in modern digital relays, of either adaptive or non-adaptive protection systems, is stated as an optimisation problem, introducing a novel mathematical formulation. An innovative solution, which takes advantage of advanced optimisation techniques, is also proposed. Recently published works dealing with this problem are thoroughly reviewed and new mathematical models are developed, considering the engineering problem at length. The developed optimisation models are integrated with state-of-the-art solvers in a versatile software package, which automates the overcurrent element coordination study. The efficacy and high performance of the proposed method, even for large-scale problems, are demonstrated through its application to standard power systems used in the relevant literature.

Supervisor: George Korres, Professor

PhD student: Vasileios Papaspiliotopoulos