￭ Placing the brake resistor
Install the resistor assembly outside the drive in a place where it is able to cool effectively.
Arrange the cooling of the resistor in a way that:
• no danger of overheating is caused to the resistor or nearby materials, and
• the temperature of the room the resistor is located in does not exceed the allowed
maximum.
Supply the resistor with cooling air or coolant according to the resistor manufacturer’s
instructions.
WARNING!
The materials near the brake resistor must be non-flammable. The surface
temperature of the resistor is high. Air flowing from the resistor is of hundreds of
degrees Celsius. If the exhaust vents are connected to a ventilation system, make
sure that the material withstands high temperatures. Protect the resistor against
contact.
￭ Protecting the system against thermal overload
The brake chopper protects itself and the resistor cables against thermal overload when
the cables are dimensioned according to the nominal current of the drive. The drive control
program includes a resistor overload protection function which can be tuned by the user.
See the firmware manual.
A main contactor is not required for protecting against resistor overheating when the resistor
is dimensioned according to the instructions and the internal brake chopper is in use. The
drive will disable power flow through the input bridge if the chopper remains conductive in
a fault situation but the charging resistor may fail.
Note: If an external brake chopper (outside the drive module) is used, a main contactor is
always required.
A thermal switch is required for safety reasons. The standard resistors available as option
+D151 are equipped with a thermal switch. The switches of the resistors are wired in series
and connected in the Run enable loop of the drive. With custom resistors, a similar protection
must be implemented.
Use a thermal switch cable rated as follows:
• twisted pair, shielding recommended
•
rated operating voltage between a conductor and ground (U
0
) ≥ 750 V
• insulation test voltage > 2.5 kV.
Wire the switch to a digital input on the drive control unit. Consider connecting the thermal
switch in the Run enable loop connected to the DIIL input. See the circuit diagrams of the
drive.
264 Resistor braking
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