4-22 BE1-951 Protection and Control 9328900990 Rev L
Table 4-10. Definitions for Equations 4-2 and 4-3
Parameter Description Explanation
T
T
Time to trip Time that the 51 function will take to time out and trip.
D Time dial setting Time dial setting for the 51 function.
M Multiple of pickup
Measured current in multiples of pickup. The timing algorithm has a
dynamic range of 0 to 40 times pickup.
A
Coefficient specific
to selected curve
Affects the effective range of the time dial.
B
Coefficient specific
to selected curve
Affects a constant term in the timing equation. Has greatest effect
on curve shape at high multiples of tap.
C
Coefficient 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 curve
shape near pickup.
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.
K Constant Characteristic minimum delay term.
T
R
Time to reset Relevant if 51 function is set for integrating reset.
R
Coefficient specific
to selected curve
Affects the speed of reset when integrating reset is selected.
Setting Programmable Curves
Curve coefficients are entered using the SP-CURVE (Settings Protection-programmable curve)
command.
Table 4-11 lists the programmable curve settings.
Table 4-11. Programmable Time Current Characteristic Curve Coefficients
Setting Range Increment Default
A Coefficient 0 to 600 0.0001 0.2663
B Coefficient 0 to 25 0.0001 0.0339
C Coefficient 0.0 to 1.0 0.0001 1.0000
N Coefficient 0.5 to 2.5 0.0001 1.2969
R Coefficient 0 to 30 0.0001 0.5000
Curve coefficients can also be entered using BESTCOMS.
Select the Curve Coefficients button on the 51 tab in the
Overcurrent Protection screen (refer to
Figure 4-16). The Curve
Coefficients screen will appear. See
Figure 4-18. Enter the
calculated values for each constant and select Done.
Programmable curve coefficients can be entered regardless of
the curve chosen for the protection element. However, the
programmable curve will not be enabled until P is selected as
the curve for the protective element.
Figure 4-18. Curve Coefficients Screen
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