Calculation Of Braking Power - Danfoss VLT Brake Resistor MCE 101 Design Manual

System Integration
DC-link Voltage (U
Size [V]
FC 301 3x200-240
FC 301 3x200-240
FC 302 3x200-240
4 4
FC 301 3x380-480
FC 301 3x380-480
FC 302 3x380-500
FC 302 3x380-500
FC 302 3x525-600
FC 302 3x525-600
FC 302 3x525-690
Table 4.4 DC-link Voltage (U
1) Enclosure type A
2) Enclosure types B, C
3) Enclosure types A, B, C
4) Enclosure types D, E, F
DC-link Voltage (U
Size [V]
FC 360 3x380-480,
0.37-22 kW
FC 360 3x380-480, 30-75
kW
Table 4.5 DC-link Voltage (U
1) Adjustable with 2-14 Brake voltage reduce
2) No built-in brake option
DC-link Voltage (U
Size [V]
FCD 302 3x380-480
Table 4.6 DC-link Voltage (U
DC-link Voltage (U
Size [V]
VLT 2800 3x200-240
VLT 2800 3x380-480
Table 4.7 DC-link Voltage (U
16
Design Guide
), FC 301/FC 302
dc
High
Brake
voltage
active
warning
[V DC]
[V DC]
1)
365 405
2) 390 405
390 405
1) 728 810
2) 778 810
3) 810 840
4) 810 828
3) 943 965
4) 1099 1109
1099 1109
), FC 301/FC 302
dc
), FC 360
dc
High
Brake
voltage
active
warning
[V DC]
[V DC]
1) 800
700-770
N/A 2) 800
), FC 360
dc
), FCD 302
dc
High
Brake
voltage
active
warning
[V DC]
[V DC]
778 810
), FCD 302
dc
), VLT 2800
dc
High
Brake
voltage
active
warning
[V DC]
[V DC]
385 400
770 800
), VLT 2800
dc
Danfoss A/S © Rev. 05/2014 All rights reserved.
Use the brake resistance R
converter is able to brake at the highest braking torque
Over
(M ) (e.g. 160%). The formula is written as:
br(%)
voltage
alarm
[V DC]
R
Ω =
rec
P
motor
410
η is typically at 0.90
motor
410
η is typically at 0.98
VLT
410
820
When a higher brake resistor resistance is selected, 160%/
820
150%/110% braking torque cannot be obtained, and there
855
is a risk that the frequency converter cuts out of DC-Link
855
overvoltage for protection.
975
1130 For braking at lower torque, for example 80% torque, it is
possible to install a brake resistor with lower power rating.
1130
Calculate size using the formula for calculating R

4.1.3 Calculation of Braking Power

When calculating the braking power, ensure that the brake
resistor is scaled for the average power as well as the peak
power.
•
The average power is determined by the process
Over
period time, i.e. the length of the braking time in
voltage
relation to the process period time.
alarm
•
The peak power is determined by the braking
[V DC]
torque, which means that as braking progresses,
800 the brake resistor must be able to dissipate the
energy input.
800
Illustration 4.2 shows the relation between the average
power and the peak power.
P
[W]
Over
voltage
alarm
[V DC]
820
T Process period time in s
p
T Braking time in s
b
Over
voltage
Illustration 4.2 Relation between Average Power and Peak
alarm
Power
[V DC]
410
820
, to ensure that the frequency
rec
2
U dc x 100
x M br x η x η
% VLT motor
P
peak
P
avg
T T
p b
.
rec
t [s]
MG90O202