Danfoss VLT AutomationDrive FC 300 Design Manual page 57

Product Introduction
NOTICE!
Check that the brake resistor can handle 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
guarantees that the adjustable frequency drive is able to
brake at the highest braking torque (M
formula can be written as:
2
U dc x 100
R
Ω =
rec
P x Mbr x η x η
%
motor
DRIVE motor
η is typically at 0.90
motor
η is typically at 0.98
DRIVE
For 200 V, 480 V, 500 V, and 600 V adjustable frequency
drives, R at 160% braking torque is written as:
rec
107780
V : Rrec =
200 Ω
Pmotor
464923
500 V : Rrec = Ω
Pmotor
630137
600 V : Rrec = Ω
Pmotor
832664
690 V : Rrec = Ω
Pmotor
NOTICE!
The resistor brake circuit resistance selected should not
be higher than that recommended by Danfoss. D-F size
adjustable frequency drives contain more than one brake
chopper and must use one brake resistor per brake
chopper.
NOTICE!
If a short circuit occurs in the brake transistor, power
dissipation in the brake resistor is only prevented by
using a line power switch or contactor to disconnect line
power from the adjustable frequency drive. The
contactor can be controlled by the adjustable frequency
drive.
WARNING
FIRE HAZARD
Brake resistors can get very hot while/after braking, and
must be placed in a secure environment to avoid fire
risk.
MG34S222
Design Guide
3.8.4 Control with Brake Function
The brake is protected against short-circuiting of the brake
resistor, and the brake transistor is monitored to ensure
that short-circuiting of the transistor is detected. A relay/
digital output can be used to protect the brake resistor
. This
rec
against overloading by generating a fault in the adjustable
frequency drive.
) of 160%). The
br(%)
In addition, the brake makes it possible to read out the
momentary power and the mean power for the latest 120
s. The brake can also monitor the power energizing and
make sure that it does not exceed the limit selected in
2-12 Brake Power Limit (kW). Use 2-13 Brake Power
Monitoring to select what function occurs when the power
transmitted to the brake resistor exceeds the limit set in
2-12 Brake Power Limit (kW).
Monitoring the braking energy is not a safety function; a
thermal switch is required for that purpose. The brake
resistor circuit is not protected against ground leakage.
Over Voltage Control (OVC) can be selected as an
alternative brake function in 2-17 Over-voltage Control. This
function is active for all units and ensures that if the DC
link voltage increases, the output frequency also increases
to limit the voltage from the DC link, thereby avoiding a
trip.
NOTICE!
OVC cannot be activated when running a PM motor,
while 1-10 Motor Construction is set to [1] PM non-salient
SPM.
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
CAUTION
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