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Calculating the maximum braking power
The P
value for each standard brake chopper and brake resistor combination is given
brmax
in the rating table on page 57. The rated value is specified for a reference braking cycle
(10 s of braking, 50 s of rest). If the actual braking cycle does not correspond to the
reference cycle, you have to calculate the maximum allowed braking power as shown
below.
1. Braking energy transferred during any ten minute period must be less than or equal to
the energy transferred during the reference braking cycle:
n · P
· t
< P
br
br
brmax
where:
n
Number of braking pulses during a ten minute period
P
Maximum allowed braking power (kW)
br
t
Braking time (s)
br
P
Maximum braking power for a reference cycle (kW)
brmax
2. The braking power must not exceed the rated maximum value P
P
< P
br
brmax
Example 1
The duration of a braking cycle is 30 minutes. The braking time is 15 minutes.
Result: If the braking time exceeds ten minutes, the braking is considered continuous. The
allowed continuous braking power is ten percent of the maximum braking power (P
Example 2
The duration of a braking cycle is three minutes. The braking time is 40 seconds.
P
· 100 s
brmax
1.
<
P
br
4 · 40 s
P
br
P
brmax
t
br
T = Duration of the braking cycle
2.
P
< P
O.K.
br
brmax
Result: The maximum allowed braking power for the cycle is 62% of the rated value given
for the reference cycle.
· 100 s
=
0.625 · P
brmax
Planning the electrical installation 29
t
600 s
:
brmax
).
brmax
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