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1) For frequency converters ≤ 7.5 kW shaft output
2) For frequency converters 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 frequency converter 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 mains switch or contactor to disconnect the
mains for the frequency converter. (The contactor can be
controlled by the frequency converter).
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 frequency converters contain more
than one brake chopper. Consequently, use one brake
resistor per brake chopper for those enclosure types.
5.5.2 Brake Resistor Cabling
EMC (twisted cables/shielding)
To meet the specified EMC performance of the frequency
converter, use screened cables/wires. If unscreened wires
are used, it is recommended to twist the wires to reduce
the electrical noise from the wires between the brake
resistor and the frequency converter.
For enhanced EMC performance, use a metal screen.
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
frequency converter.
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 energising 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 brake power is not a safety function; a
thermal switch is required for that purpose. The brake
resistor circuit is not earth leakage protected.
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 frequency converter 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
).
System Integration
VLT
®
AutomationDrive FC 301/FC 302 Design Guide, 0.25-75 kW
MG33BF02 - Rev. 2013-12-20
57
5
5
Содержание VLT AutomationDrive FC 301
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