Basler Electric DECS-250N - Manual (Page 65)

9440500990 Rev D 49
DECS-250N Protection
during overexcitation. The field current must fall below the dropout ratio (95%) for the function to begin
timing to reset. The following equations are used to calculate the field overcurrent pickup and reset time
delays.
𝑡
𝑝𝑖𝑐𝑘𝑢𝑝
=
𝐴 × 𝑇𝐷
𝐵 + √𝐶 + 𝐷 × 𝑀𝑂𝑃
Equation 9. Inverse Field Overcurrent Pickup
Where:
t
pickup
= time to pick up in seconds
A = -95.908
B = -17.165
C = 490.864
D = -191.816
TD = time dial setting <0.1, 20>
MOP = multiple of pickup <1.03, 205>
𝑇𝑖𝑚𝑒
𝑟𝑒𝑠𝑒𝑡
=
0.36 × 𝑇𝐷
(𝑀𝑂𝑃
𝑟𝑒𝑠𝑒𝑡
) 2 − 1
Equation 10. Inverse Field Overcurrent Reset
Where:
Time
reset
= maximum time to reset in seconds
TD = time dial setting <0.1, 20>
MOP
reset
= multiple of pickup <1.03, 205>
Primary and secondary setting groups provide additional control for two distinct machine operating
conditions.
Field overcurrent protection can be enabled and disabled E without altering the pickup and time delay
settings. Field overcurrent pickup and trip elements in BESTlogicPlus can be used in a logic scheme to
initiate corrective action in response to the condition. BESTCOMSPlus field overcurrent settings are
illustrated in Figure 37. In BESTCOMSPlus, a plot of the field overcurrent setting curve is displayed. The
plot can display the primary or secondary setting curves.