Danfoss VLT AutomationDrive FC 301 Series Design Manual page 64

System Integration
The intermittent duty cycle for the resistor is calculated as
follows:
Duty cycle = t
T = cycle time in s
t is the braking time in s (of the cycle time)
b
Load
5 5
Speed
ta
Figure 5.8 Typical Braking Cycle
200–240 V
PK25-P11K
P15K-P37K
380–500 V
PK37-P75K
P90K-P160
P200-P800
525–600 V
PK75-P75K
525–690 V
P37K-P400
P500-P560
P630-P1M0
Table 5.9 Braking at High Overload Torque Level
1)
650 hp [500 kW] at 86% braking torque/750 hp [560 kW] at 76%
braking torque
2)
650 hp [500 kW] at 130% braking torque/750 hp [560 kW] at 115%
braking torque
Danfoss offers brake resistors with duty cycles 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 is used on
dissipating excess heat.
NOTICE!
Make sure the resistor is designed to handle the
required braking time.
62
/T
b
tc tb to ta tc tb to ta
T
Time
Braking duty
Cycle time (s) cycle at
100% torque
120 Continuous
300 10%
120 Continuous
600 Continuous
600 40%
120 Continuous
600 40%
600 1)
40%
600 40%
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:
ED duty cycle =
where tb is the braking time in seconds and T cycle is the
total cycle time.
The brake resistance is calculated as shown:
Rbr Ω =
where
P = P
peak
The brake resistance depends on the intermediate circuit
Braking duty
voltage (U
cycle at over
The FC 301 and FC 302 brake function is settled in four
torque
areas of line power.
(150/160%)
Size
40%
10%
FC 301/FC 302
200–240 V
40%
FC 301
10%
380–480 V
10%
FC 302
380–500 V
40% FC 302
525–600 V
10%
FC 302
2)
10%
525–690 V
10%
Table 5.10 Brake Limits [UDC]
NOTICE!
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
that guarantees that the adjustable frequency drive is able
to brake at the highest braking torque (M
The formula can be written as:
R
Ω =
rec
η is typically at 0.90
motor
η is typically at 0.98
DRIVE
Rev. 2014-04-04 All rights reserved.
tb
T cycle
2
U dc
Ppeak
x M [%] x η x η
motor br motor VLT
).
dc
Brake active Warning before
cut-out
390 V 405 V
778 V 810 V
810 V 840 V
943 V 965 V
1084 V 1109 V
2
U dc x 100
P x Mbr x η x η
%
motor DRIVE motor
[W]
Cut-out
(trip)
410 V
820 V
850 V
975 V
1130 V
, i.e., one
rec
) of 160%.
br(%)
MG33BF22