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
rec
. This
guarantees that the adjustable frequency drive is able to
brake at the highest braking torque (M
br(%)
) of 160%). The
formula can be written as:
R
rec
Ω =
Udc
2 x 100
P
motor
x Mbr
%
xη
DRIVE
x η
motor
η
motor
is typically at 0.90
η
DRIVE
is typically at 0.98
For 200 V, 480 V, 500 V, and 600 V adjustable frequency
drives, R
rec
at 160% braking torque is written as:
200
V : Rrec = 107780
Pmotor Ω
500
V : Rrec = 464923
Pmotor Ω
600
V : Rrec = 630137
Pmotor Ω
690
V : Rrec = 832664
Pmotor Ω
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.
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
against overloading by generating a fault in the adjustable
frequency drive.
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)
.
CAUTION
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
.
Product Introduction
Design Guide
MG34S222
Danfoss A/S © Rev. 2014-02-10 All rights reserved.
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