Basler Electric DGC-2020 - Manual (Page 178)

Programmable Curves for Overcurrent Protection
Inverse overcurrent characteristics for trip and reset programmable curves are defined by Equation 4-1
and 4-2 respectively. These equations comply with IEEE Std C37.112-1996 - IEEE Standard Inverse-
Time Characteristic Equations for Overcurrent Relays. The curve-specific coefficients are defined for the
standard curves as listed in Appendix A, Time Overcurrent Characteristic Curves. When inverse time
overcurrent characteristic curve P is selected, the coefficients used in the equation are those defined by
the user. Definitions for these equations are provided in Table 4-6.
Equation 4-1. Time OC Characteristics for Trip
( ) K BD
C M
AD
T
Q
N
T
+ +
−
=
Equation 4-2. Time OC Characteristics for Reset
| 1 M |
RD
T
2 R −
=
Table 4-6. Definitions for Equations 4-1 and 4-2
Parameter Description Explanation
T
T
Time to trip Time that the 51-x function will take to time out and trip.
D Time dial setting Time dial setting for the 51-x 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 pickup.
C
Coefficient specific to
selected curve
Affects the multiple of pickup where the curve would
approach infinity if allowed to continue below pickup. Has
greatest effect on curve shape near pickup.
N
Multiple of Pickup
exponent specific to
selected curve
Affects how inverse the characteristics are. Has greatest
effect on curve shape at low to medium multiples of pickup.
K Constant Characteristic minimum delay term. Fixed at 0.028.
T
R
Time to reset Relevant if 51-x function is set for integrating reset.
R
Coefficient specific to
selected curve
Affects the speed of reset when integrating reset is selected.
Q
Denominator exponent
specific to selected curve. Affects how inverse the characteristics are. Has greater
affect as Q is increased.
Setting Programmable (P) Curves
Curve coefficients J are entered using BESTCOMSPlus. Table 4-7 lists the programmable curve settings.
Table 4-7. 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 to 1 0.0001 1.0000
N Coefficient 0.5 to 2.5 0.0001 1.2969
Q Coefficient 0.1 to 10 0.0001 1.0000
R Coefficient 0 to 30 0.0001 0.5000
4-68 DGC-2020 BESTCOMSPlus
® Software
9400200990 Rev X