12
Resistor braking
Contents of this chapter
The chapter describes how to select the brake resistor and cables, protect the system,
connect the brake resistor and enable resistor braking.
Safety
WARNING!
Do not do work on the brake resistor or the resistor cable when the drive is
energized. A dangerous voltage is present in the resistor circuit, even when the
brake chopper is not operating, or when it is disabled by a parameter.
Operation principle
The brake chopper handles the energy generated by a decelerating motor. The extra
energy increases the DC link voltage. The chopper connects the brake resistor to the
intermediate DC circuit whenever the voltage in the circuit exceeds the limit defined by
the control program. Energy consumption by the resistor losses lowers the voltage until
the resistor can be disconnected.
Selecting the brake resistor
Drives have a built-in brake chopper as standard equipment. The brake resistor is
selected using the table and equations shown in this section.
1.
Determine the required maximum braking power P
Rmax
for the application. P
Rmax
must be smaller than P
BRmax
. Refer to Reference brake resistors (page 175).
2.
Calculate resistance R with Equation 1.
3.
Calculate energy E
Rpulse
with Equation 2.
Resistor braking 173
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