Danfoss VLT AutomationDrive FC 300 Design Manual page 44

3. Introduction to FC 300
3
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 brake power 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 mains:
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
Danfoss recommends the brake resistance
R , i.e. one that guarantees that the fre-
rec
quency converter is able to brake at the high-
est braking torque (M
formula can be written as:
η
motor
44
Brake active
390 V (UDC)
778 V
810 V
943 V
NB!
Check 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.
) of 160%. The
br(%)
is typically at 0.90
MG.33.B9.02 - VLT
2
U
dc
R
Ω =
br
P
peak
where
P = P x M x η
peak motor br
Warning before cut
out
405 V
810 V
840 V
965 V
R
Ω =
rec
P
motor
η is typically at 0.98
VLT
® is a registered Danfoss trademark
FC 300 Design Guide
x η [W]
motor VLT
).
dc
Cut out (trip)
410 V
820 V
850 V
975 V
2
U x 100
dc
x M x x
η η
br ( % ) VLT motor