Danfoss VLT AutomationDrive FC 301 Series Design Manual page 65

System Integration
For 200 V, 480 V, 500 V and 600 V adjustable frequency
drives, R at 160% braking torque is written as:
rec
107780
200 V : Rrec = Ω
Pmotor
375300
Ω 1
480 V : Rrec =
Pmotor
428914
Ω 2
V : Rrec =
480
Pmotor
464923
V : Rrec =
500 Ω
Pmotor
630137
V : Rrec =
600 Ω
Pmotor
832664
690 V : Rrec = Ω
Pmotor
1)
For adjustable frequency drives ≤ 10 hp [7.5 kW] shaft
output
2) For adjustable frequency drives 15–100 hp [11–75 kW] shaft
output
NOTICE!
The resistor brake circuit resistance selected should not
be higher than that recommended 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 adjustable frequency drive cuts out for
safety reasons.
NOTICE!
If a short circuit in the brake transistor occurs, power
dissipation in the brake resistor is only prevented by
using a line switch or contactor to disconnect the line
power for the adjustable frequency drive. (The contactor
can be controlled by the adjustable frequency drive).
CAUTION
The brake resistor gets hot during and after braking.
•
To avoid personal injury, do not touch the
brake resistor.
•
Place the brake resistor in a secure environment
to avoid fire risk.
CAUTION
Enclosure types D-F adjustable frequency drives contain
more than one brake chopper. Consequently, use one
brake resistor per brake chopper for those enclosure
types.
MG33BF22
Design Guide
5.5.2 Brake Resistor Cabling
EMC (twisted cables/shielding)
To meet the specified EMC performance of the adjustable
frequency drive, use shielded cables/wires. If non-shielded
wires are used, it is recommended to twist the wires to
reduce the electrical noise from the wires between the
brake resistor and the adjustable frequency drive.
For enhanced EMC performance, use a metal shield.
5.5.3 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 for protecting the brake resistor
against overloading in connection with a fault in the
adjustable frequency drive.
In addition, the brake enables reading out the momentary
power and the mean power for the latest 120 s. The brake
can also monitor the power energizing and ensure that it
does not exceed the limit selected in 2-12 Brake Power
Limit (kW). In 2-13 Brake Power Monitoring, select the
function to carry out when the power transmitted to the
brake resistor exceeds the limit set in 2-12 Brake Power
Limit (kW).
NOTICE!
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.
Overvoltage control (OVC) (exclusive brake resistor) can be
selected as an alternative brake function in 2-17 Over-
voltage Control. This function is active for all units. The
function ensures that a trip can be avoided, if the DC link
voltage increases. This is done by increasing the output
frequency to limit the voltage from the DC link. It is a
useful function, e.g., if the ramp-down time is too short
since tripping of the adjustable frequency drive is avoided.
In this situation, the ramp-down time is extended.
NOTICE!
OVC cannot be activated when running a PM motor
(when 1-10 Motor Construction is set to [1] PM non salient
SPM).
Rev. 2014-04-04 All rights reserved.
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