Power grid protection against geomagnetic disturbances (GMD)

This paper describes the design, construction and testing of a protective electrical system which is an effective and reliable solution for blocking the DC current in the neutral of grounded “Y” configured power transformers. The blocking design uses sensors and electronic controls to automatically remove a metallic grounding path, leaving a capacitive blocking device in the transformer neutral connection. The sensing electronics detects the quasi-DC current in the transformer neutral or the total harmonic distortion (THD) on the grid, resulting from a geomagnetic disturbance (GMD); thus activating the protective mode of operation. In practice it is anticipated that this protective system will operate in the capacitively grounded mode of operation less than 0.1% of the time which limits the probability of experiencing a ground fault while in the capacitive blocking mode.