5-2 9424200996
Phase Undervoltage (27P) Protection BE1-11m
Table 5-1. Definitions for Equation 5-1 and Equation 5-2
Time that the 27P-x function will take to time out and trip.
Time dial setting for the 27P-x function.
M Multiple of pickup
Measured current in multiples of pickup. The timing algorithm has
a dynamic range of 0 to 1 times pickup.
A
Constant specific to
selected curve
Affects the effective range of the time dial.
B
Constant specific to
selected curve
Affects a constant term in the timing equation. Has greatest effect
on curve shape at high multiples of tap.
C
Constant specific to
selected curve
Affects the multiple of PU where the curve would approach
infinity if allowed to continue below pickup. Has greatest effect on
N
Exponent specific to
selected curve
Affects how inverse the characteristics are. Has greatest effect
on curve shape at low to medium multiples of tap.
Relevant if 27P-x function is set for integrating reset.
R
Constant specific to
selected curve
Affects the speed of reset when integrating reset is selected.
Curve constants are entered on the Undervoltage (27P) settings screen in BESTCOMSPlus.
Programmable curve constants can be entered only when the P curve is chosen for the protection
element from the Curve drop-down menu.
Table Curves
BESTCOMSPlus is used to set the 27P element Table Curves (T1, T2, T3, and T4). Using the Settings
Explorer within BESTCOMSPlus, open the Protection, Voltage, Undervoltage Table Curves, Table Curve
(1, 2, 3, or 4) tree branch and select the table curve to be modified. Refer to Figure 5-1. A minimum of 2
and maximum of 40 points can be entered for any one T curve. When you are satisfied with the values
chosen, select Save Curve. Use the Settings Explorer to browse to the 27P-x element you wish to
program and use the drop-down menu under Curve to select T1, T2, T3, or T4.
Table curves can be entered regardless of the curve chosen for the protection element. However, the
table curve will not be enabled until T1, T2, T3, or T4 is selected as the curve for the protective element.
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