GE MiCOM P40 Agile Technical Manual

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Application Notes P44x/EN AP/Hb6MiCOM P40 Agile P442, P444 (AP) 5-93The start-up of the high-speed algorithms are confirmedUnder such circumstances, the low voltage could not be explained by normal voltageexcursion tolerances on-load. A fault is definitely present on the phase in question, and it isacceptable to override the blinder action and allow the distance zones to trip according to theentire zone shape. The benefit is that the resistive coverage for faults near to the IEDlocation can be higher.For security, it is highly recommended that the blinder is Enabled, especially for lines above150 km (90 miles), to prevent non-harmonic low-frequency transients causing loadencroachment problems, and for any networks where power swings might be experienced.The impedance blinder radius i.e. Rloading as shown in the figure below. This is often taken as 120% overloading in one line,multiplied by two to account for increased loading during outages or fault clearance in anadjacent parallel circuit. Then an additional allowance for measuring tolerances results in arecommended setting typically 1/3rd of the rated full load current:Figure 63: Load blinder settingZ < (Rated phase voltage Vn)/(IFLC x 3) , Therefore;R< Blinder Lim < (Rated phase voltage Vn * Cosß)/(IFLC x 3)FLC = Full Load CurrentWhen the load is at the worst-case power factor, it should remain below the beta setting. So,if we assume a typical worst-case 0.85 power factor, then:ß > Cos-1 (0.85) plus 15° margin > 47°and to ensure that line faults are detected, ß < (Line Angle -15°).In practice, an angle half way between the worst-case leading load angle, and the protectedline impedance angle, is often used.The undervoltage setting“ Load Blinder V< “ must be lower than the lowest phase-neutralvoltage under heavy load flow and depressed system voltage conditions. The typicalmaximum V< setting is 70% Vn.Load Blinder V<