ABB ACS850-04 series, Hardware Manual

Page: 157 / 164

Resistor braking
157
Protecting the system in fault situations
Thermal overload protection
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 and resistor cable thermal 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 (standard in ABB resistors) is required for safety reasons. The
cable must be shielded and not longer than the resistor cable.
Short-circuit protection
The input fuses will also protect the resistor cable when it is dimensioned according
to the input cable.
Selecting and routing the brake circuit cables
Use the cable type used for drive input cabling (see page 57 ) to ensure that the input
fuses will also protect the resistor cable. Alternatively, two-conductor shielded cable
with the same cross-sectional area can be used.
Minimizing electromagnetic interference
Follow these rules in order to minimise electromagnetic interference caused by the
rapid current changes in the resistor cables:
• Shield the braking power line completely, either by using shielded cable or a
metallic enclosure. Unshielded single-core cable can only be used if it is routed
inside a cabinet that efficiently suppresses the radiated RFI emissions.
• Install the cables away from other cable routes.
• Avoid long parallel runs with other cables. The minimum parallel cabling
separation distance should be 0.3 meters.
• Cross the other cables at right angles.
• Keep the cable as short as possible in order to minimise the EMC emissions and
stress on chopper IGBTs. The longer the cable the higher the EMC emissions,
inductive load and voltage peaks over the IGBT semiconductors of the brake
chopper.

Thermal switch
(standard in ABB re-
sistors)
Digital input of the JCU control unit.
See the firmware manual for parameter
settings.