Rockwell Automation AK DBU - Dynamic Braking Unit 600/690 VAC - Manual (Page 12)

P-8 Overview
To prevent thermal overload of the Braking Unit, it must operate within
the following limits:
In a time range of 10 minutes the permissible loading must be limited
to the maximum peak current of the DBU (300A) up to a maximum of
2.5 minutes.
This maximum current-time area of 750 Amp.-minutes can be of any
shape, as long as 300A is not exceeded.
The peak current (I
Peak
) in the following two examples is 300 Amp
(maximum current with R
min
= 3.2 ohm at 600 VAC line) and the
current-time area also meets the 750 Amp.-minutes requirement.
Figure P.4 Examples for Permissible Loading of the DBU
Permissible Loading of the DBU
1) Linear deceleration to zero speed of
a drive with high inertia connected
(e.g. centrifuge)
2) Drive with active load
(e.g. crane)
Current-time area:
(300 * 5) / 2 = 750 Amp-Min.
Current-time area:
(300 * 1) + (112.5 * 4) = 750 Amp-Min.
5
10
I
Peak
minutes
t
300A
0
4
10
I
Peak
112.5A
t
minutes
1
300A
0