Rockwell Automation 1336_F_E_T_S SERIES A CHOPPER BRAKE MODULE - Manual (Page 11)

Heavy Duty Dynamic Braking 11
1336-5.65 — March, 2007
Calculate Application Values
Use the Application Information to calculate the necessary values to choose
an acceptable Chopper Module and Dynamic Brake Resistor.
Rated Power of Motor = 100 HP
× 746 = 74.6 kW
This information is given and must be known before the calculation process
begins. If this rating is given in horsepower, convert to watts before using
in the equations.
Rated Speed = 1785 RPM = 2
π × 1785/60 = 186.93 Rad/s = ω
This information is given and must be known before the calculation process
begins. If this rating is given in RPM, convert to radians per second before
using in the equations.
Total Inertia = 9.61 kg-m 2 = J
T
If this value is given in lb-ft 2 or Wk 2 , convert to kg-m 2 before using in the
equations. Total inertia is given and does not need further calculations as
outlined in Step 2.
Deceleration Time = 6.0 seconds = (t
3
- t
2
)
Period of Cycle = 60 seconds = t
4
DC Bus Voltage = 750 Volts = V
d
This is known because the drive is rated at 460 Volts rms.
If a drive is rated 230 Volts rms, V
d
= 375 Volts.
If a drive is rated 575 Volts rms, V
d
= 937.5 Volts.
Select the Correct Chopper Module
Peak Braking Power = J
T
ω
2 /(t
3
- t
2
) = 55.96 kW = P
b
This is 75% rated power and is less than the maximum drive limit of 150%
current limit. This calculation is the result of Step 3 and determines the peak
power that must be dissipated by the Dynamic Brake Resistor.
Maximum Dynamic Brake Resistance = V
d
2 /P
b
= 10.5 ohms = R
db1
This calculation is the result of Step 4 and determines the maximum ohmic
value of the Dynamic Brake Resistor. Note that a choice of V
d
= 750 Volts
DC was made based on the premise that the drive is rated at 460 Volts.
Minimum Current Flow = V
d
/R
db1
= 74.62 amps = I
d1
This calculation is the result of Step 5. This is the minimum value of current
that will flow through the Dynamic Brake Resistor when the Chopper
Module Transistor is turned on. Refer to Table 2b in the Installation
Instructions for the Brake Chopper Module, Publication 1336-5.65. Choose
the Brake Chopper Module whose peak current capacity is greater than
74.62 amps. The correct choice must be the WB035 Chopper Module
because it has a current rating greater than 74.62 amps.