KEB COMBIVERT F5 BASIC Applications Manual page 308

Project Planning
10.1.2 Design of
Braking
Resistors
Chapter Section Page
1 10 4
The KEB COMBIVERT fitted with an external braking resistor or an external braking
option is suitable for a limited 4-quadrant operation. The braking energy, refed into the DC-
bus at generatoric operation, is dissipated over the braking transistor to the braking resistor.
The braking resistor heats up during the braking process. If it is installed in a control
cabinet sufficient cooling of the control cabinet interior and sufficient distance to the
KEB COMBIVERT must be observed.
Different braking resistors are available for the KEB COMBIVERT. Please refer to the
next page for the corresponding formula and restrictions (valid range)
1. Preset desired braking time.
2. Calculate braking time without braking resistor (t
3. If the desired braking time shall be smaller than the calculated time, it is necessay
to use a braking resistor. (t
4. Calculate braking torque (M
5. Calculate peak braking power (P
calculated for the worst case (n
6. Selection of braking resistor:
a) P > P
R
b) P is to be selected according to the cycle time (c.d.f.).
N
The braking resistors may be used only for the listed unit sizes. The maximum
cyclic duration of a braking resistor shall not be exceeded.
6 % c.d.f. = maximum braking time
25 % c.d.f. = maximum braking time
40 % c.d.f. = maximum braking time
For longer cyclic duration times special designed braking resistors are necessary.
The continuous output of the braking transistor must be taken into consideration.
7. Check, whether the desired braking time is attained with the braking resistor
(t ).
Bmin
Restriction: Under consideration of the rating of the braking resistor and the
brake power of the motor, the braking torque may not exceed 1.5times of the
rating torque of the motor.
When utilizing the maximum possible braking torque the frequency inverter must
be dimensioned for the higher current.
Date Name: Basis
10.04.02
KEB COMBIVERT F5
< t )
B Bmin
). Take the load torque into account at the calculation.
B
). The peak braking power must always be
B
to standstill).
max
B
30 s
48 s
).
Bmin
8 s
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