Example calculation, C-10 – Rockwell Automation AK DBU - Dynamic Braking Unit 600/690 VAC User Manual
Page 48
C-10
Design Information
A 250 HP, 600 Volt motor and drive are accelerating and decelerating as
depicted in
• Cycle period (t
4
) is 40 seconds
• Rated speed is 1600 RPM
• Deceleration time from rated speed to 0 speed is 2.0 seconds
• Motor load can be considered purely as an inertia and all power
expended or absorbed by the motor is absorbed by the motor and
load inertia.
• Load inertia is 44.0 lb-ft
2
directly coupled to the motor
• Motor inertia is 166 lb-ft
2
• A PowerFlex 700H, 250 HP, 600V Normal Duty rating is chosen.
• Drive efficiency is 0.975 and motor efficiency is 0.86.
Proceed with the following calculation to verify the AKDBU300 is
suitable for the application, and select the Dynamic Brake Resistor.
This information was given and must be known before the calculation
process begins. This can be given in HP, but must be converted to watts
before it can be used in the equations.
This information was given and must be known before the calculation
process begins. This can be given in RPM, but must be converted to
radians per second before it can be used in the equations.
Step 1
Total Inertia
(GR)
2
= 0
This value can be in lb.-ft.
2
or Wk
2
, but must be converted into kg-m
2
before it can be used in the equations.
Example Calculation
Rated Power
250 HP
=
746 watts
186500 W
=
×
Rated Speed
ω
b
1600
=
RPM
2
π
=
=
1600
60
----------
×
167.5 Rad
s
-----------------------
=
Lower Speed
ω
o
0
= RPM
2
π
0
60
-----
×
0 Rad
s
-------------
=
=
=
J
T
J
m
GR
2
J
L
×
(
)
+
=
J
T
166
=
.
44
+
210 lb.-ft.
2
210
0.042
8.82 kg-m
2
=
Ч
=
=