Braking - Emerson Unidrive M700 Installation Manual

A typical 3 phase motor would be connected in
however, variations on this are common e.g.
Incorrect connection of the windings will cause severe under or over fluxing of the motor, leading to a
very poor output torque or motor saturation and overheating respectively.
4.9.6 Output contactor
If the cable between the drive and the motor is to be interrupted by a contactor or circuit
breaker, ensure that the drive is disabled before the contactor or circuit breaker is opened
or closed. Severe arcing may occur if this circuit is interrupted with the motor running at
high current and low speed.
WARNING
A contactor is sometimes required to be installed between the drive and motor for safety purposes.
The recommended motor contactor is the AC3 type.
Switching of an output contactor should only occur when the output of the drive is disabled.
Opening or closing of the contactor with the drive enabled will lead to:
1. OI ac trips (which cannot be reset for 10 seconds)
2. High levels of radio frequency noise emission
3. Increased contactor wear and tear
The Drive Enable terminal when opened provides a Safe Torque Off function. This can in many
cases replace output contactors.
For further information see the Control User Guide.
4.10

Braking

Braking occurs when the drive is decelerating the motor, or is preventing the motor from gaining
speed due to mechanical influences. During braking, energy is returned to the drive from the motor.
When motor braking is applied by the drive, the maximum regenerated power that the drive can
absorb is equal to the power dissipation (losses) of the drive.
When the regenerated power is likely to exceed these losses, the DC bus voltage of the drive
increases. Under default conditions, the drive brakes the motor under PI control, which extends the
deceleration time as necessary in order to prevent the DC bus voltage from rising above a user
defined set-point.
If the drive is expected to rapidly decelerate a load, or to hold back an overhauling load, a braking
resistor must be installed.
Table 4-5 shows the default DC voltage level at which the drive turns on the braking transistor.
However the braking resistor turn on and the turn off voltages are programmable with Braking IGBT
Lower Threshold (06.073) and Braking IGBT Upper Threshold (06.074).
Table 4-5 Default braking transistor turn on voltage
Drive voltage rating
200 V
400 V
When a braking resistor is used, Pr 00.015 should be set to Fast ramp mode.
NOTE
Unidrive M/HS Frame 3 and 4 Power Installation Guide
Issue Number: 3
for 400 V operation or
∆
690 V 400 V.
DC bus voltage level
∆
for 230 V operation,
390 V
780 V
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