4–186 850 FEEDER PROTECTION SYSTEM – INSTRUCTION MANUAL
PROTECTION CHAPTER 4: SETPOINTS
Figure 4-74: Inverse Time Undervoltage Curves
If FlexCurves are selected, the operating time determined based on following equation:
T= Flexcurve (V
pkp
/ V)
NOTE:
FlexCurve reverses the ratio of voltages. The ratio of set pickup value to the measured
voltage.
Example: For a Pickup set to 0.9 x VT, when the measured voltage is 0.82 x VT, the ratio
would be 0.9/0.8 = 1.1, therefore in the FlexCurve, the corresponding Trip time setting entry
is at 1.1 x PKP (not at 0.82 x PKP). On the other hand, when the measured voltage is 1 x VT,
the ratio is 0.9/1 = 0.9, therefore, in the FlexCurve, the corresponding Reset time entry is at
0.9 x PKP.
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