Planning The Braking System - ABB ACS880-37 Hardware Manual

238 Resistor braking

Planning the braking system

Verifying the capacity of the braking equipment

1. Calculate the maximum power generated by the motor during braking (P
2. Ensure that the braking power of the chopper is equal to or greater than P
The P values specified in the ratings table on page
brmax
braking cycle (1 minute of braking, 9 minutes of rest). If the actual duty cycle does not
correspond to the reference cycle, the maximum allowed braking power (P
used instead. In the ratings table, P
below for instructions on calculating P
3. Check the resistor selection. The energy generated by the motor during a 400-second
period must not exceed the heat dissipation capacity of the resistor (E
If the E of the resistor is not sufficient, it is possible to use a four-resistor assembly in
R
which two resistors are connected in parallel, two in series. The E
resistor assembly is four times that of a single resistor.
Custom resistors
Resistors other than those available as option +D151 can be used provided that
•
the resistance is not lower than the value given in the ratings table (page 237)
WARNING! Never use a brake resistor with a resistance below the value specified
for the particular drive / brake chopper / resistor combination. The drive and the
chopper would not able to handle the overcurrent caused by the low resistance.
•
the resistance of the custom resistor does not restrict the braking capacity needed, ie.
P <
max
where
P
max
U
DC
R
•
the heat dissipation capacity E
3 above).
2
U
DC
R
Maximum power generated by the motor during braking
Voltage over the resistor during braking. U
1.35 · 1.25 · 415 V DC (when supply voltage is 380 to 415 V AC)
1.35 · 1.25 · 500 V DC (when supply voltage is 440 to 500 V AC) or
1.35 · 1.25 · 690 V DC (when supply voltage is 525 to 690 AC)
Resistor resistance (ohm)
of the resistor is sufficient for the application (see step
R
is given for two additional braking cycles. See
br
for other braking cycles.
br
equals
DC
).
max
max
237 are for the reference
br
).
R
value of the four-
R
.
) must be