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Placing the brake resistors
Install the resistors in a place where they will cool.
Arrange the cooling of the resistor in a way that:
•
no danger of overheating is caused to the resistor or nearby materials
•
the temperature of the room the resistor is located in does not exceed the allowed
maximum.
Supply the resistor with cooling air/water 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, ensure that the material withstands high temperatures. Protect the resistor against
contact.
Selecting the chopper enable input cable
Make sure that the cable connecting the resistor thermal switch to chopper enable input
X1 meets the following requirements:
•
shielded cable
•
rated operating voltage between a core and ground > 750 (U
•
insulation test voltage > 2.5 kV.
Protecting the system against thermal overload
The drive control program includes a resistor and resistor cable thermal protection
function, which can be tuned by the user. The brake chopper protects itself and the resistor
cables against thermal overload, provided that the following conditions are met:
•
the resistor assembly is equipped with a thermal switch, which is connected to
chopper enable input X1 (see page 38)
•
fault indication relay output X3 is wired to the main contactor circuit of the drive (see
page 26)
•
the cables are dimensioned according to the nominal current of the drive.
Operation principle
If the resistor overheats, its thermal switch opens and interrupts the chopper enable input
signal. The signal is internally wired to the chopper control board via a temperature
sensitive switch. Upon a fault, the relay output either opens the drive main circuit breaker
or gives a fault indication to the overriding control system, which takes care of the
protection.
For more information on the thermal protection function, see the appropriate drive
firmware manual.
Protecting the resistor cable against short-circuits
The brake chopper unit requires the use of brake circuit fuses. The fuses protect the brake
chopper and the brake circuit cables in a cable short-circuit situation.
Planning the electrical installation 31
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