6KBU300
—————— DIMENSIONING... AND CORRESPONDING... —————— 4
1
4. DIMENSIONING OF THE BRAKING UNIT ANDCORRESPONDINGRESISTORWhat below indicated should be meant in general, because point 6 reports a list of the normalised resistor which
must be used with the braking units of the series 6KBU300-.. for the supposed conditions.
Taking into account that:
PPBR [W] Peak power while braking
PNBR [W] Rated power of the resistor
EBR [J] Braking energy
VBR [V] Braking voltage threshold
IPBR [A] Peak braking current
IAVBR [A] Average braking current
IPBU [A] Peak current of the braking unit
n1, n2 [RPM] Initial and final speed
tBR, T [S] Braking time and cycle time
JTOT [Kg* m2] Total moment of inertia (referred to the motor shaft )
We will have:
P=J*n*
PBR TOT 1
n-n
t
12
BR
2Π
60
f001
*
I=
PBR
P
PBR
V
BR f003
E=
BR
(n -n )
12
22
J
TOT
2Π
2
2
60
**()
Ohmic value of the resistor:
f004
R=
BR ≤VBR
IPBR
Rated continuous power of the resistor: P=
NBR =
P*t
PBR BR EBR
2T T
f005
Attention! The value calculated here has to be considered carefully:
the formula calculates an average power value which may be considerably different
from the istantaneous power in case of very low duty-cycles.
Normally, resistors are not able to sustain a peak power greater than 5 to 10 times their rated
power. For this reason if the duty-cycles are less than 10%, the value calculated here can not
be used as rated power of the resistor and considerations made at 4.1 and 6 have to be taken
into account. Consult your resistor manufacturer for overload capability of resistors.