Statistical Design of Experiments for Power System Protection Testing: A Case Study for Distance Relay Performance Testing

In modern power systems, testing protection systems and equipment before the field implementation is vital to ensure the correct operation and guarantee reliability, quality and security of electricity supply. This paper focuses on the performance testing of the distance protection, whose state-of-the-art test methodologies (including the recommendations of the IEC 60255-121:2014 standard) can quickly lead to time/money resource limitations. As budget-wise considerations should not justify an "arbitrary" or "convenient" selection of which and how many tests to perform, this paper shows how the current testing methodologies benefits from the statistical design of experiments (stat-DOE). It is proven how the stat-DOE supports the performance testing in the efficient selection of the optimal tests to conduct, in the systematic investigation of the effect of different factors, and in the robust definition of pass/fail criteria for specifying acceptance tests. A step-to-step practical guideline for adopting the stat-DOE is offered to conduct a realistic performance testing, accounting for operator-specific requirements (e.g., maximum affordable number of tests) and physical constraints among factors. The results allow to propose lines of refinement and recommendations for the stakeholders. Finally, not only this paper serves as a guide to replicate the performance testing of other protection functions or in alternative scenarios, but it also ultimately paves the way for the routine adoption of the stat-DOE in the definition and refinement of test methodologies for power system protection testing at large towards the achievement of a standardized basis for it.