Danfoss FC 300 Design Manual page 47

FC 300 Design Guide
The intermittent duty cycle for the resistor is calculated as follows:
Duty cycle = t
T = cycle time in seconds
t is the braking time in seconds (of the cycle time)
b
Danfoss offers brake resistors with duty cycle of 5%, 10% and 40%. If a 10% duty cycle is applied,
the brake resistors are able to absorb braking energy for 10% of the cycle time. The remaining
90% of the cycle time will be used on dissipating excess heat.
The max. permissible load on the brake resistor is stated as a peak power at a given intermittent
duty cycle and can be calculated as:
The brake resistance is calculated as shown:
As can be seen, the brake resistance depends on the intermediate circuit voltage (U
The FC 301 and FC 302 brake function is settled in 4 areas of the line power:
Size
FC 301 / 302 3 x 200-240
V
FC 301 3 x 380-480 V
FC 302 3 x 380-500 V
FC 302 3 x 525-600 V
/T
b
Brake active
390 V (UDC)
778 V
810 V
943 V
NOTE
Make sure that the brake resistor can cope with a voltage of 410 V, 820 V, 850 V or
975 V - unless Danfoss brake resistors are used.
MG.33.B9.22 - VLT ® is a registered Danfoss trademark.
3. Introduction to FC 300
2
U
dc
R
Ω =
br
P
peak
where
P = P x M x η
peak motor br motor
Warning before cut Cut out (trip)
out
405 V 410 V
810 V 820 V
840 V 850 V
965 V 975 V
3
x η [W]
VLT
).
dc
47