Example Calculation - Allen-Bradley PowerFlex Reference Manual

Example Calculation

A 10 HP, 4 Pole, 480 Volt motor and drive is accelerating and
decelerating as depicted in
• Cycle period t
4
• Rated speed is 1785 RPM and is to be decelerated to 0 speed in 15.0
seconds
• Motor load can be considered purely as inertia, and all power
expended or absorbed by the motor is absorbed by the motor and
load inertia
• Load inertia is 4.0 lb.-ft.
• Motor rotor inertia is 2.2 lb.-ft.
Calculate the necessary values to choose an acceptable Dynamic Brake.
Rated Power
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.
Rated Speed
Lower Speed
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.
Total Inertia
This value can be in lb.-ft.
before it can be used in the equations.
Deceleration Time
Figure 2.1.
is 40 seconds
2
and is directly coupled to the motor
2
×
10 HP
=
ω
1785 RPM
= =
b
ω
0 RPM
= =
o
J 6.2
= =
T
2 2
or Wk , but must be converted into kg-m
(
t
=
3
Period of Cycle t
=
746 watts 7.46 kW
=
1785
186.98 Rad
×
2π ----------
= = -------------------------
60
0 0 Rad
×
2π
= ---- - = ------------ -
60
2
lb.-ft. 0.261 kg-m
=
)
t 15 seconds
– =
2
40 seconds
=
4
2-9
s
s
2
2