NORD Drivesystems BU0200 - Manual (Page 34)

2 Assembly and installation
BU 0200 GB-4411 Subject to technical alterations 33
2.3 Brake resistor (BR)
During dynamic braking (frequency reduction) of a three phase motor, electrical energy is returned to the
frequency inverter. In order to avoid switch-off of the FI due to excess voltage and internal or external
braking resistor can be used. With this, the integrated brake chopper (electronic switch) pulses the link
circuit voltage (switching threshold approx. 420V/720V DC, according to the mains voltage) into the braking
resistor. Here the excess energy is converted into heat.
For input voltages >460V the use of a brake resistor is generally recommended in order to compensate for
the reduced storage capacity of the link circuit due to the higher voltage.
CAUTION
The braking resistance and all other metal components can heat up to temperatures above
70°C.
When mounting, sufficient distance from neighbouring components must be maintained.
When working on the components, allow sufficient cooling time beforehand
2.3.1 Internal brake resistor SK BRI4-
…
The internal brake resistor can be used if only slight, short braking phases are to be expected. For the
individual power ranges of size 4, the item includes a set of 2 brake resistors. These must be connected in
parallel and thereby achieve the electrical data from the description of the material (see also Section 2.3.4).
The mounting location for the second brake resistor is opposite to the mounting location of the first brake
resistor.
The output power of the SK BRI4 is limited (see also the following note field) and can be calculated as
follows.
)² ) / 30 ( 1 ( * tbrake Pn P
 
, however, P < P
max
(P=Brake power (W), Pn= Continuous brake power of resistor (W), Pmax. peak brake power, tbrake = duration of braking process (s))
The permissible continuous brake power Pn must not be exceeded in the long-term average.
(For details of Pn and Pmax, see Section 2.3.4)
NOTE
With the use of internal resistors, the DIP switch 8 must be set to “On”. This is important in
order to activate a limitation of the peak power of the brake resistor. Otherwise, the brake
resistor may be damaged during operation.
Alternatively, a suitable power limit can also be set in P555, P556 and P557. However, this
is only effective if DIP 8 is set to the “Off” position.