218
Operating Instructions ACU
09/08
17.4.1 Dimensioning of Brake Resistor
The following values must be known for dimensioning:
−
Peak braking power P
b Peak
in W
−
Resistance R
b
in
Ω
−
Operation Time OT in %
•
Calculation of peak braking power P
b Peak
(
)
b
2
2
2
1
Peak
b
t
182
n
n
J
P
⋅
−
⋅
=
P
b Peak
= Peak braking power in W
J
= Moment of inertia of drive system kgm
2
n
1
= Speed of drive system before the braking oper-
ation in min
-1
n
2
= Speed of drive system after the braking opera-
tion in min
-1
t
b
= Braking time in s
•
Calculation of resistance R
b
Peak
b
2
BC
d
b
P
U
R
=
R
b
= Resistance in
Ω
U
d BC
= Switch-on threshold in V
P
b Peak
= Peak braking power in W
The switch-on threshold U
d BC
is the DC link voltage at which the brake resistor is
switched on. The switch-on threshold can be set, as described above, via parameter
Trigger threshold
506
.
Caution!
The resistance of the brake resistor must not be less than the minimum
value R
b min
-10%. The values for R
b min
are listed in chapter "Technical
Data".
If the calculated resistance R
b
of the brake resistor is between two standard series
values, the lower resistance is to be selected.
•
Calculation of operation time OT
cycle
t
b
t
C
D
=
OT
= Operation time
t
b
= Braking time
t
cycle
= Cycle time
t
cycle
t
b
Example:
t
b
= 48 s, t
cycle
= 120 s
%
40
4
.
0
cycle
t
b
t
C
D
=
=
=
In the case of infrequent short braking operations, typical values of the operation
time OT are at 10 %, for long braking operations (
≥
120 s) typical values are at
100%. In the case of frequent deceleration and acceleration operations, it is recom-
mended that the operating time OT be calculated according to the above formula.
The calculated values for P
b Peak
, R
b
and OT can be used by the resistor manufactur-
ers for determining the resistor-specific permanent power.
Warning!
The brake resistor is to be connected according to the specifications and
instructions in chapter "Electrical Installation, Connection of a Brake
Resistor".
Operating Instructions ACU
09/08
218
Summary of Contents for Bonfiglioli Vectron ACTIVE CUBE ACU 201 Series
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