Cutler-Hammer Digitrip OPTIM 550 - Sample of Partial Time-Current Trip Curve

I.B. 29C891B
Page 21
Effective 11/98
Before discussing protection functions individually, keep
in mind that combining functional capabilities, such as
long, short and instantaneous, is a coordination activity.
The effects of one set of settings on another set should
be carefully evaluated to determine if the results for all
possible circumstances are acceptable.
Example:
• Consider programming the protective functions of a
400 ampere Series C L-Frame circuit breaker with an
installed 200 ampere rating plug value (I
n
). OPTIM
trips are set up with actual values of current instead of
per unit settings.
• The Long Delay Setting (I
r
) is to be 100 amperes and
the Short Delay Pickup is to be 200 amperes.
• The Long Delay Setting (I
r
) is programmable from 0.4
- 1.0 times the rating plug value (I
n
) for the L-Frame.
For this example, the Long Delay Setting (I
r
) is pro-
grammed to 0.5 (I
n
) = 0.5 (200) = 100 amperes, the
required Long Delay Setting (I
r
).
• The Short Delay Pickup is programmable from 1.5 -
8.0 times the Long Delay Setting (I
r
) for the L-Frame.
For this example, the Short Delay Pickup is pro-
grammed to 2.0 (I
r
) = 2.0 (100) = 200 amperes, the
required Short Delay Pickup.
TIME
CURRENT
Intermediate
Minimum
Maximum
Figure 3-2 Typical Trip Curve Horizontal Movement
TIME
CURRENT
I
4
t Slope
I
2
t Slope
Figure 3-3 Typical Long Delay Time Slope Adjustment
TIME
CURRENT
(Pickup Accuracy)
Actual pickup will
occur within ± % of
any selected pickup
setting
(Timing Accuracy)
Actual Trip Time
will be within ± %
of any selected trip
time setting
Trip Time
Setting
Pickup Setting
Figure 3-1 Sample of Partial Time-Current Trip Curve