Resistor Simplified Sizing - gefran BUy-1020 Manuel D'utilisation

4.4. Resistor Simplified Sizing

In case all the above mentioned data are not available, it is possible to carry out a simplified
and rough calculation of the braking resistance.
The following formulas can be used for the calculation of the different braking values:
Calculating the resistance value for one inverter :
- braking peak current = 100A (125A) , see table in chapter 3
- 400Vac power supply (575Vac), see table in chapter 3.3
- braking threshold = 680 Vac (965Vac), see table in chapter 3.3
the result is:
This formula states just the ohmic value; the following considerations, on the contrary, refer
to the resistor power:
The braking resistor is normally used with an intermittent cycle; it is therefore normal to use
a resistor power lower than the one obtained through R
The following diagram can be used to define the overload factor (similar diagrams can be
supplied by the producer of the used resistor).
1000
100
10
0,1
Using this diagram to calculate the value of the continuous (rated) power of the braking
resistor, it is possible to apply the following formula:
Continuative power R
59-GB
R [ ] =
BR
R =
BR
RESISTANCE POWER
1
1 2 3 4 5
OVERLOAD FACTOR
—————— Braking Unit ——————
V [V]
W
BR
I [I]
PBR
680
?
= 6.8
100
* I
BR PBR
6 7 8 9 10
Regenerated power
=
BR
Overload factor
.
2
Pause time
15 seconds
30 seconds
1 minute
5 minutes
30 minutes