Danfoss FC 300 Design Manual page 41

FC 300 Design Guide
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:
P = P x M
PEAK MOTOR BR(%)
As can be seen, the brake resistance depends on the intermediate circuit voltage (UDC).
The FC 301 and FC 302 brake function is settled in 3 areas of mains:
Size
FC 301 / 302 3 x 200-240 V 390 V (UDC)
FC 301 3 x 380-480 V
FC 302 3 x 380-500 V
FC 302 3 x 525-600 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.
Danfoss recommends the brake resistance R
i.e. one that guarantees that the frequency con-
verter is able to brake at the highest braking tor-
que (M ) of 160%. The formula can be written as:
br
η is typically at 0.90
motor
For 200 V, 480 V, 500 V and 600 V frequency converters, R
107780
V R
200 : =
rec
P
M otor
375300
V R
380 : =
P
M otor
464923
500 V : R =
rec
P
M otor
630137
V R
600 : =
rec
P
M otor
832664
V R
690 : =
rec
P
M otor
1. For FC 300 frequency converters ≤ 7.5 kW shaft output
2. For FC 300 frequency converters > 7.5 kW shaft output
NB!
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 frequency converter cuts out for safety
reasons.
NB!
If a short circuit in the brake transistor occurs, power dissipation in the brake resistor is only
prevented by using a mains switch or contactor to disconnect the mains for the frequency
converter. (The contactor can be controlled by the frequency converter).
Introduction to FC 300
x η x η [W]
MOTOR VLT
Brake active
778 V
810 V
943 V
REC
Ω
Ω
Ω
Ω
Ω
MG.33.B7.02 - VLT is a registered Danfoss trademark
2
U dc
R
= =
br
P
peak
Warning before cut out Cut out (trip)
405 V
810 V
840 V
965 V
,
R
=
rec
P x M
motor
η is typically at 0.98
VLT
at 160% braking torque is written as:
REC
428914
V R
480 : =
P
M otor
Ω
410 V
820 V
850 V
975 V
2
U dc x
100
x x
ϕ ϕ
BR ( % ) VLT motor
Ω
= Ω
41