Unsymmetrical faults and their potential for nuisance tripping of embedded generators

A growing number of embedded generation (EG) schemes are being connected in parallel with utility systems. As the influence of these noncentrally dispatched generators continues to rise, it is becoming more important to maintain safety and reliability of the host supply. In order to assess the effects of disturbances on EG, simulation and practical tests were conducted for unsymmetrical faults: single line-to-ground, line-to-line and double line-to-ground, applied to a small test system. This paper reports on the results of tests of line-to-line and double line-to-ground faults. The work reported in this paper outlines the effect of unsymmetrical faults on the operation of the G59 protection and the stability of synchronous generators. The main focus is the G59 requirement that phase voltage excursions outside limits of -10% and +10% for over 0.5 seconds are not permitted