Technical Data
28 BA8230
2.5.2.2 Braking resistors The mean braking capacity and the duty cycle are determined for selecting the
braking resistor (assuming braking is required). In addition, the minimum braking
resistor or the maximum braking power of each 8230 frequency inverter with a power
dump must be observed.
Determining the mean braking capacity:
Power: Energy content of one braking process:
W
B
= 0,0055 J x (n
1
2
- n
2
2
)[W
B
]= Ws
[J] = kgm²
[n
1
, n
2
]= min
-1
Mean braking power for the complete braking process:
P
BV
= W
B
/t
B
[P
BV
]= W
[t
B
]= s
The braking resistor is rated for the mean braking power and the duty cycle permitted
according to the resistor.
If several braking processes occur during a load cycle, the individual mean braking
powers P
BV1
, P
BV2
.... P
BVn
must be calculated and related to the cycle time t
c
.
The resultant effective mean braking power P
BVeff
must match the continuous capacity
of the braking resistor:
∗++∗+∗
=
c
bn
2
BVnb2
2
BV2b1
2
BV1
BVeff
t
tP...tPtP
P
The continuous capacity of the braking resistor must at least match the mean braking
capacity P
BV
or P
BVeff
respectively as shown above.
Important!
The brake resistors used must be monitored thermally by an overload protection. The
brake resistors offered by Lenze have an integrated temperature monitoring. When
using several resistors in parallel, the individual monitoring contacts must be
connected in series (normally-closed contacts).
Note:
When determining the rating of a braking resistor the type of load involved is an
important criterion.
The size of the braking resistor for a sudden load is determined only by the weight of
the active material and for the theoretical continuous power only by the radiating
surface of the resistor material.
In discontinuous operation the rating is determined by the power permitted and the
duty cycle. The values shown in Table 13 for the duty cycle are preferred and, unless
stated otherwise, refer to a maximum duty cycle of 15 s.
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