Rockwell Automation AK DBU - Dynamic Braking Unit 600/690 VAC User Manual
Page 49
Design Information
C-11
DC Bus Regulation Voltage = V
d
= 950 Volts
This was known because the drive is rated at 600 Volts rms.
All of the preceding data and calculations were made from knowledge of
the application under consideration. The total inertia was given and did
not need further calculations as outlined in
Step 2 Calculate the Peak Braking Power (
P
b
) and (
P
b1
) then
compare (
P
b1
) to the Peak Braking Power of the DBU (
P
max
)
P
b1
= P
b
x (motor effic. x drive effic.)
P
b1
= 123 700 x (0.975 x 0.86) = 103 722 watts < P
max
Note that this is 56% of rated power and is less than the maximum drive
limit of 150% current limit. This calculation determines the power that
must be dissipated by the Dynamic Brake Resistor.
The DBU is suitable for this application because P
b1
is less than P
max
.
Step 3 Calculate the Average Braking Power
Verify the power rating of the Dynamic Brake Resistor, or if applicable
the sum of the power ratings of the Dynamic Brake Resistors chosen in
is greater than the value calculated in
.
Deceleration Time
t
3
t
2
–
(
)
2 seconds
=
=
Cycle Period
t
4
40 seconds
=
=
Peak Braking Power
P
b
J
T
ω
b
ω
b
ω
o
–
(
)
[
]
t
3
t
2
–
(
)
----------------------------------------
=
=
P
b
8.82 167.5 167.5
0
–
(
)
[
]
2
-----------------------------------------------------
123700 watts
=
=
Average Braking Power
P
av
t
3
t
2
–
(
)
t
4
------------------
P
b
2
-----
ω
b
ω
o
+
(
)
ω
b
------------------------
=
=
P
av
2
40
-----
⎝ ⎠
⎛ ⎞ 123700
2
----------------
⎝
⎠
⎛
⎞ 167.5 0
+
167.5
---------------------
⎝
⎠
⎛
⎞
4120 watts
=
=