Eaton PowerXL DA1 Series Installation Manual page 63

Because of this, and as a simplification, brake resistors are instead usually
classified for two load groups:
•
•
DC+
~
Mains
=
Figure 33: Braking cycle, fast motor stop with external brake resistor
Selecting brake resistors
The selection of brake resistors takes place according to the occurring
sustained power loss P
The brake resistor must be appropriate for both outputs.
The maximum pulse power is defined by the braking torque – kinetic energy
W
kin
simplified procedure, as a guideline value for dimensioning for the impulse
peak output P
the rated motor output can be used, as the mechanical braking output is
reduced by the efficiency level of the motor and the inverter.
The required rated output and continuous rating of the braking resistance
P
DB
If the kinetic energy is not known, the percentage ratio of braking time
t
braking
The required continuous rating for a duty factor of 10 % = DF[%]),
for example, can be calculated as follows:
DA1 Variable Frequency Drives 08/18 MN04020005Z-EN www.eaton.com
Low duty: Low load with short braking duration and low duty factor (up
to about 25 %), e.g., for horizontal conveyors and handling equipment
for bulk cargo and general cargo, end carriages, sliding doors, and
turbomachinery (centrifugal pumps, fans).
High duty: High load with long braking duration and high duty factor
(at least 30 %), e.g., for elevators, downhill conveyors, winders,
centrifuges, flywheel motors, and large fans.
R
B
BR
=
~
DB
during braking – that is fed back by the motor during braking. In the
, the braking output P
Peak
is calculated from the braking energy W
and cycle time t
C
n
Motor
M
P
P
PEAK
P
RD
and the maximum impulse peak output P
of the variable frequency drive or
max
1 W
kin
P ∼ P = x
Peak max
2 t
Braking
kin
W
kin
P =
DB
t
C
is required:
t
Brake
DF[%] = x 100 %
t
C
P = P x 10 %
DB Peak
2 Engineering
2.6 Brake resistors
t t
Brems OFF
t
C
and the cycle time :
C
t
t
t
Brems
.
Peak
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