Dimensioning Of The Braking Resistor; Installation Of The Braking Resistor - WEG DBW03 Serie Manual Del Usuario

3.3.2 Dimensioning of the Braking Resistor

For the proper dimensioning of the braking resistor, consider the application data,
such as:
Desired deceleration time.
„
Load inertia.
„
Braking cycle.
„
In any case, the effective current and maximum braking current values presented in
table 7.1 must be observed.
The maximum braking current defines the minimum ohm value allowed for the braking
resistor. The DC link voltage level for actuation of the rheostatic braking is defined by
the setting of the DIP Switch S2 (rheostatic braking actuation voltage); see table 3.4.
The braking resistor power is defined according to the deceleration time, load inertia
and resistive torque.
For most applications, it may be used a resistor with the ohm value indicated in table
7.1 and power of 20 % of the rated power value of the driven motor.
Use resistors of STRIP or WIRE type in ceramic support, with proper insulation voltage
and that stand high instant powers in relation to the rated power.
For critical applications with very short braking times, high inertia loads (ex: centrifuges)
or with very short and frequent duty cycles, contact WEG, to define the most suitable
resistor.
Note:
The effective braking current presented is just an orientative value, because it depends
on the braking cyclic ratio in the application. In order to obtain the effective braking
current, use the formula below, where t
sum of the braking actuation periods during the severest cycle of five minutes.

3.3.3 Installation of the Braking Resistor

Connect the braking resistor between the power terminals +UD and BR, see figure 3.5.
Separate these power cables from the signal and control wiring. Dimension the cables
according to the application, observing the maximum and effective currents.
If the braking resistor is mounted within the inverter cabinet, take its energy into
account when dimensioning the ventilation of the cabinet.
In order to avoid the destruction of the resistor or risk of fire, include a thermal relay in
series with the resistor and/or a thermostat in contact with its housing, connected in
such a way to disconnect the input power supply of the inverter, as shown in figure 3.5.
is given in minutes and corresponds to the
br
√
t
I = I x
br
effective max
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Installation and Connection
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