User`s guide

171
CHAPTER 8 - CFW-08 OPTIONS AND ACCESSORIES
8.23
DYNAMIC BRAKING
The dynamic braking is used where short deceleration times
are required or where high inertia is present.
For the correct sizing of the braking resistor, application data
such as, deceleration time, load inertia, braking duty cycle
must be considered.
In any case, the rms current capacityand the maximum peak
current must be considered.
The maximum peak current defines the minimum permitted
ohmic value for the braking resistor. Refer to table 8.5.
The DC link voltage level for the actuation of the dynamic
braking is as follows:
Inverters supplied with 200 V to 240 V:
375 Vdc
Inverters supplied with 380 V to 480 V:
750 Vdc
8.23.1
Resistor Sizing
The brakingtorque, thatcanbe obtainedthrough the frequency
inverter, withoutusing thedynamicbraking module,varies from
10 % to 35 % of the rated motor torque.
During the deceleration process, the kinetic energy of theload
is regenerated into the inverter DC link. This energy loads up
the capacitors by increasing the DC link voltage. When this
energy is not fully dissipated, it may generate a DC link
overvoltage trip (E01) and disabling the inverter.
To obtain higher braking torques, the use of dynamic braking
is recommended where the excess of the regeneratedenergy
is dissipated in a resistor mounted externally to the inverter.
The braking resistor is defined according to the deceleration
time, load inertia and resistive torque.
In most cases, a resistor with an ohmic value as indicated on
the table below and a power rating of 20 % of the driven motor
can be used.
Use wire type or tape type resistors with suitable insulation to
withstand the instantaneous currentpeaks.
Figure 8.30
- Load reactor connection
R
S
T
PE
PE
R
S
T
U
V
W
U
V
W
PE
Disconnecting
Switch
PE
Load
Reactor
Shield