NORD Drivesystems BU0180 - Manual (Page 25)

2 Assembly and installation
BU 0180 GB-0914 Pre-series version 25
2.3 Brake resistor (BR)
(only size 2)
During dynamic braking (frequency reduction) of a three phase motor, electrical energy is returned to the
frequency inverter. From Size II or larger, an internal or external brake resistor may be used to prevent the
FI from shutting down in case of overvoltage. 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. The brake resistor ultimately converts the excess energy 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- …
NOTE
The internal brake resistor may only be installed at the factory and can not be retrofitted.
It is essential that this is taken into account for the configuration an ordering of the device.
The internal brake resistor can be used if only slight, short braking phases are to be expected.
The output power of the SK BRI4 is limited (see also the following note field) and can be calculated as follows.
)² ) / 30 ( 1 ( * tbrakes Pn P
 
, however, P < P
max
(P=Brake power (W), Pn= Continuous brake power of resistor (W), Pmax. peak brake power, tbrakes = duration of braking process (s))
The permissible continuous brake power P
n
must not be exceeded in the long-term average.
(For details of P
n
and P
max
see Section 2.3.4)
NOTE
If internal brake resistors are used, a suitable power limit must be set in P555, P556 and
P557. This is important in order to activate a peak and continuous power limit for the brake
resistor. Otherwise, the brake resistor may be damaged during operation.