GE Industrial Solutions 6KBU300 Braking Unit User Manual
Page 19
6KBU300
—————— DIMENSIONING... AND CORRESPONDING... ——————
4
1
4. DIMENSIONING OF THE BRAKING UNIT AND
CORRESPONDING RESISTOR
What 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:
P
PBR
[W]
Peak power while braking
P
NBR
[W]
Rated power of the resistor
E
BR
[J]
Braking energy
V
BR
[V]
Braking voltage threshold
I
PBR
[A]
Peak braking current
I
AVBR
[A]
Average braking current
I
PBU
[A]
Peak current of the braking unit
n
1
, n
2
[RPM]
Initial and final speed
t
BR
, T [S]
Braking time and cycle time
J
TOT
[Kg* m2]
Total moment of inertia (referred to the motor shaft )
We will have:
P = J
* n *
PBR
TOT
1
n -n
t
1
2
BR
2Π
60
f001
*
I =
PBR
P
PBR
V
BR
f003
E =
BR
(n -n )
1
2
2
2
J
TOT
2Π
2
2
60
*
*
(
)
Ohmic value of the resistor:
f004
R =
BR
≤
V
BR
I
PBR
Rated continuous power of the resistor:
P =
NBR
=
P * t
PBR
BR
E
BR
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.