58
Sigmatek FDD Sizes 7 to 9 Power Installation Guide
4.6.6
Output contactor
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
.
4.7
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 the motor is being braked 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 4-6 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).
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
Summary of Contents for 074.00660
Page 1: ...Power Installation Guide SIGMATEK FDD Frame 7 to 9 Issue 12...
Page 97: ......
Page 98: ...0478 0641 12...
