![background image](http://html.mh-extra.com/html/danfoss/fc-300/fc-300_design-manual_507599046.webp)
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:
Rbr
Ω
=
Udc
2
Ppeak
where
P
peak
= P
motor
x M
br
[%] x
η
motor
x
η
VLT
[W]
As can be seen, the brake resistance depends on the intermediate circuit voltage (U
dc
).
The AutomationDrive FC 301 and AutomationDrive FC 302 brake function is settled in 4 areas of line power:
Size
Brake active
Warning before cut out
Cut out (trip)
AutomationDrive FC 301 /
AutomationDrive FC 302 3 x 200–240 V
390 V (UDC)
405 V
410 V
AutomationDrive FC 301 3 x 380–480 V 778 V
810 V
820 V
AutomationDrive FC 302 3 x 380–500 V* 810 V/ 795 V
840 V/ 828 V
850 V/ 855 V
AutomationDrive FC 302 3 x 525–600 V 943 V
965 V
975 V
AutomationDrive FC 302 3 x 525–690 V 1084 V
1109 V
1130 V
* Power size dependent
NOTE!
Check that the brake resistor can cope with a voltage of 410 V, 820 V, 850 V, 975 V or 1130 V - unless Danfoss brake resistors are
used.
Danfoss recommends the brake resistance R
rec
, i.e., one that guarantees
that the adjustable frequency drive is able to brake at the highest braking
torque (M
br(%)
) of 160%. The formula can be written as:
Rrec
Ω
=
Udc
2
x
100
Pmotor
x
Mbr
(%)
x
VLT
x
motor
η
motor
is typically at 0.90
η
VLT
is typically at 0.98
For 200 V, 480 V, 500 V and 600 V adjustable frequency drives, R
rec
at 160% braking torque is written as:
200
V
:
Rrec
= 107780
Pmotor
Ω
480
V
:
Rrec
= 375300
Pmotor
Ω
1)
480
V
:
Rrec
= 428914
Pmotor
Ω
2)
500
V
:
Rrec
= 464923
Pmotor
Ω
600
V
:
Rrec
= 630137
Pmotor
Ω
690
V
:
Rrec
= 832664
Pmotor
Ω
1) For adjustable frequency drives
≤
10 hp [7.5 kW] shaft output
2) For adjustable frequency drives with 15–100 hp [11–75 kW] shaft output
NOTE!
The resistor brake circuit resistance selected should not be higher than that recommended by Danfoss. If a brake resistor with a higher
ohmic value is selected, the 160% braking torque may not be achieved because there is a risk that the adjustable frequency drive cuts
out for safety reasons.
3 Introduction to AutomationDrive FC 300
FC 300 Design Guide
3-30
MG.33.BC.22 - VLT
®
is a registered Danfoss trademark
3