Standard size PFVL141C-20,0MN 3BSE024994R2000

Standard size PFVL141C-20,0MN 3BSE024994R2000

Standard size PFVL141C-20,0MN 3BSE024994R2000

In some cases the load impedance might enter the zone characteristic without any fault on the protected line. The phenomenon is called load encroachment and it might occur when an external fault is cleared and high emergency load is transferred on the protected line. The effect of load encroachment is illustrated in the left part of figure 202. A load impedance within the characteristic would cause an unwanted trip.

The traditional way of avoiding this situation is to set the distance zone resistive reach with a security margin to the minimum load impedance. The drawback with this approach is that the sensitivity of the protection to detect resistive faults is reduced. The IED has a built-in function which shapes the characteristic according to the right part of figure 202. The load encroachment algorithm will increase the possibility to detect high fault resistances, especially for phase-to-earth faults at remote line end. For example, for a given setting of the load angle ArgLd the resistive blinder for the zone measurement can be expanded according to the right part of the figure 202, given higher fault resistance coverage without risk for unwanted operation due to load encroachment. This is valid in both directions.