Danfoss VLT AutomationDrive FC 300 Design Manual page 45

FC 300 Design Guide
For 200 V, 480 V, 500 V and 600 V frequency converters, R
as:
V
200
V
480
V
500
V
600
V
690
1) For FC 300 frequency converters ≤ 7.5 kW shaft output
2) For FC 300 frequency converters > 7.5 kW shaft output
3.7.2. Control with Brake Function
The brake is to limit the voltage in the intermediate circuit when the motor acts as a generator.
This occurs, for example, when the load drives the motor and the power accumulates on the DC
link. The brake is built up as a chopper circuit with the connection of an external brake resistor.
Placing the brake resistor externally offers the following advantages:
-
-
-
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 for protecting the brake resistor against overloading in connection with a fault in the
frequency converter.
In addition, the brake makes it possible to read out the momentary power and the mean power
for the latest 120 seconds. The brake can also monitor the power energizing and make sure it
107780
R
: = Ω
rec
P
motor
375300
1 )
R
: = Ω
rec
P
motor
464923
R
: = Ω
rec
P
motor
630137
R
: = Ω
rec
P
motor
832664
R
: = Ω
rec
P
motor
NB!
The resistor brake circuit resistance selected should not be higher than that recom-
mended by Danfoss. If a brake resistor with a higher ohmic value is selected, the
160% braking torque may not be achieved because there is a risk that the frequency
converter cuts out for safety reasons.
NB!
If a short circuit in the brake transistor occurs, power dissipation in the brake resistor
is only prevented by using a mains switch or contactor to disconnect the mains for
the frequency converter. (The contactor can be controlled by the frequency con-
verter).
NB!
Do not touch the brake resistor as it can get very hot while/after braking.
The brake resistor can be selected on the basis of the application in question.
The brake energy can be dissipated outside the control panel, i.e. where the energy can
be utilized.
The electronics of the frequency converter will not be overheated if the brake resistor is
overloaded.
MG.33.B9.02 - VLT ® is a registered Danfoss trademark
3. Introduction to FC 300
at 160% braking torque is written
rec
428914
V R
480 : =
rec
P
motor
2 )
Ω
3
45