Planning The Braking System; Verifying The Load Capacity Of The Braking Equipment; Custom Resistor; Calculating The Maximum Braking Power For A Custom Duty Cycle - ABB ACS880-07 Hardware Manual

Planning the braking system

Verifying the load capacity of the braking equipment

￭
Calculate the maximum power generated by the motor during braking ( P
1.
2. Ensure that the maximum power rating of the braking equipment is equal to or
greater than P
max
The P values specified in the ratings table are for the reference braking cycle
brmax
(1 minute of braking, 9 minutes of rest). If the actual duty cycle does not correspond
to the reference cycle, either use the power rating given for the other two reference
cycles ( P
), or calculate the maximum braking power for a custom braking cycle.
br
See 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 you use custom resistor(s), see also the separate instructions below.
R
If the E value of the resistor is not sufficient, it is possible to use a four-resistor
R
assembly in which two resistors are connected in parallel, two in series. The E
value of the four-resistor assembly is four times that of a single resistor.

Custom resistor

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
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 < U 2
/R
max DC
where
P Maximum power generated by the motor during braking
max
U Voltage over the resistor during braking. UDC equals
DC
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 V AC)
R Resistor resistance (ohm)
• the heat dissipation capacity E
(see step 3 above).

Calculating the maximum braking power for a custom duty cycle

These rules must be met during any braking cycle:
.
of the resistor is sufficient for the application
R
for other braking cycles.
br
Resistor braking 337
).
max
R