Impact of Grid-Forming Converters on Distance Elements Based on the X and M Calculations

This paper studies the performance of the distance elements employing the X- and M-calculation convention of the SEL-T401L relay in grids 100% powered by grid-forming converters (GFCs). It was observed that the GFCs do not impact the security of the ground distance (21G) and phase distance (21P) elements. Nonetheless, high-resistance faults close to the reach point can affect the dependability of the 21G elements that use the quadrilateral operating characteristic. Also, the dependability of the 21P elements that use the mho operating characteristic is affected by high-resistance faults, which is expected because of the mho feature. It was also found that the fault-ride-through strategy implemented in the considered GFCs does not have a negative effect on the estimation of the apparent loop impedance. These findings are obtained via electromagnetic transient simulations in PSCAD.