Danfoss oers 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 is used to dissipate
excess heat.
NOTICE!
Make sure that the resistor is designed to handle the
required braking time.
The maximum allowed load on the brake resistor is stated
as a peak power at a given intermittent duty cycle. The
brake resistance is calculated as shown:
R
br
Ω =
U
dc
2
P
peak
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 DC-
link voltage (U
dc
).
Voltage Brake
active
Warning before cut
out
Cut out
(trip)
380–480 V
1)
810 V 828 V 855 V
525–690 V 1084 V 1109 V 1130 V
Table 10.23 FC 102 Brake Limits
1) Power size dependent
NOTICE!
Check that the brake resistor can handle a voltage of
410 V, 820 V, 850 V, 975 V, or 1130 V. Danfoss brake
resistors are rated for use on all Danfoss drives.
Danfoss recommends the brake resistance R
rec
. This
calculation guarantees that the drive is able to brake at the
highest braking torque (M
br(%)
) of 150%. The formula can
be written as:
R
rec
Ω =
U
dc
2
x100
P
motor
xM
br( % )
xη
VLT
xη
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 drives, R
rec
at 160%
braking torque is written as:
200
V: R
rec
=
107780
P
motor
Ω
500
V: R
rec
=
464923
P
motor
Ω
600
V: R
rec
=
630137
P
motor
Ω
690
V: R
rec
=
832664
P
motor
Ω
NOTICE!
The resistor brake circuit resistance selected should not
be higher than what is recommended by Danfoss.
Enclosure sizes E1h–E4h contain 1 brake chopper.
NOTICE!
If a short circuit occurs in the brake transistor, or a
ground fault occurs in the brake module or wiring,
power dissipation in the brake resistor is prevented only
by using a mains switch or contactor to disconnect the
mains from the drive, or a contact in the brake circuit.
Uninterrupted power dissipation in the brake resistor can
cause overheating, damage, or a re.
WARNING
FIRE HAZARD
Brake resistors get hot while/after braking. Failure to
properly place brake resistor in a secure location can
result in serious injury or property damage.
•
Place brake resistor in a secure environment
away from ammable objects and accidental
contact.
10.7.2 Control with Brake Function
A relay/digital output can be used to protect the brake
resistor against overloading or overheating by generating a
fault in the drive. If the brake IGBT is overloaded or
overheated, the relay/digital signal from the brake to the
drive turns o the brake IGBT. This relay/digital signal does
not protect against a short circuit in the brake IGBT or a
ground fault in the brake module or wiring. If a short
circuit occurs in the brake IGBT, Danfoss recommends a
means to disconnect the brake.
In addition, the brake makes it possible to read out the
momentary power and the average power for the latest
120 s. The brake can monitor the power energizing and
make sure that it does not exceed the limit selected in
parameter 2-12 Brake Power Limit (kW). Parameter 2-13 Brake
Power Monitoring selects what function occurs when the
power transmitted to the brake resistor exceeds the limit
set in parameter 2-12 Brake Power Limit (kW).
Electrical Installation Con... Design Guide
MG22B222 Danfoss A/S © 01/2018 All rights reserved. 169
10 10
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