Rockwell Automation AK DBU - Dynamic Braking Unit 600/690 VAC User Manual
Page 43
Design Information
C-5
Step 2
Peak Braking Power
P
b
=
Peak braking power (watts). 1.0 HP = 746 watts
P
b1
=
P
b
x (motor efficiency x drive efficiency)
J
T
=
Total inertia reflected to the motor shaft (kg-m
2
)
η
M
,
η
D
= Motor and drive efficiency
ω
b
=
Rated angular rotational speed
ω
o
=
Angular rotational speed,
less than rated speed down to zero
N
b
=
Maximum application motor speed (RPM)
t
3
– t
2
=
Deceleration time from
ω
b
to
ω
o
(seconds)
Calculate Peak Braking Power:
Record the Peak Braking Power:
Calculate P
b1
:
P
b1
= P
b
x (motor efficiency x drive efficiency)
Compare the P
b1
to the Maximum Peak Braking Power of the DBU
(P
max
). If P
b1
is greater than P
max
, the decel time must be increased, or
the inertia or the speed must be decreased, so that the drive does not
enter current limit.
Table C.A DC bus Voltage and Minimum Brake Resistance
For the purposes of this document, it is assumed that the motor used in
the application is capable of producing the required regenerative torque
and power.
P
b
=
Line Voltage
V
d
R
P
max
600 VAC
950 VDC
3.2 Ohms
268 kW
690 VAC
1090 VDC
3.7 Ohms
305 kW
P
b
J
T
ω
b
ω
b
ω
o
–
(
)
[
]
t
3
t
2
–
(
)
----------------------------------------
=
Rad
s
---------
2
πN
b
60
------------
=
Rad
s
---------
P
b
ooooo
[
]
oooooo
[
]
ooooo
ooooo
–
(
)
Ч
Ч
ooooooooo
ooooooooo
–
(
)
------------------------------------------------------------------------------------------------
=