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Drawing the Load encroachment characteristic

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A region may be defined as Load Encroachment, along with the graphical distance characteristic.

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The Load Encroachment scheme prevents the impedance area from entering the distance characteristic and finally prevents unwanted trip.

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This area usually overlaps with the trip area and is often activated only for three-phase fault loops.

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For this purpose, after adding the protection zones,

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add two more zones to be used as Load Encroachment Blinder.

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We place these zones on “Non tripping” and fault loop on L1-L2-L3.

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This characteristic requires three elements that can be Line Cartesian, Arc Cartesian or Arc Polar type.

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For each element, just hit add Element and select its type.

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For example, in the Siemens 7SA522 relay, we drawing the specifications of Load Encroachment by using elements 1241, 1242,

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1243 and 1244.

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For this purpose, we need three “Line Cartesian” components.

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The first component is a line that extends through the source, with coordinates R=65.36, X=58.85 and an angle of 42+180=222 degrees.

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The second component with R=65.36 and X=0 has an angle of 270 degrees, perpendicular to the horizontal axis.

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The third component of the Cartesian have coordinates R=65.36, X=-58.85 and -42 degree angle.

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You can create the final characteristic by disabling the Auto Close option.

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In order to draw the Load Encroachment characteristic on the left side of the Distance characteristic,

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we create three Cartesian components with specifications R=-65.36, X=-58.85 with an angle of 42 degrees, R=-65.36, X=0 with an angle of 90 degrees,

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and finally, R=-65.36, X=58.85 with an angle of 138 degrees.

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As mentioned above, during the test, we will not see trip issued in this area.