Digitax HD M75X Series Installation and Technical Guide
57
Issue Number: 5
4.7.4 /
motor operation
The voltage rating for and
connections of the motor should always be checked before attempting to run the motor.
The default setting of the motor rated voltage parameter is the same as the drive rated voltage, i.e.
400 V drive 400 V rated voltage
230 V drive 230 V rated voltage
A typical 3 phase motor would be connected in for 400 V operation or
for 230 V operation, however, variations on this are common e.g.
690 V
400 V. 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.
4.7.5 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 STO1, STO2 terminal when opened, provides a Safe Torque Off function. This can in many cases replace output contactors.
For further information see the relevant
Digitax HD M75X
Control User Guide
.
4.8 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 4-9 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 4-9 Default braking transistor turn on voltage
When a braking resistor is used, Pr
02.004
should be set to Fast ramp mode.
4.8.1 Compact braking resistor
A resistor has been designed to be mounted on the side of the drive.
See section 3.13.1
on page 32 for mounting details. The design of the resistor is such that no thermal protection circuit is
required, as the device will fail safety under fault conditions. The in built software overload protection is set-up at default for the designated compact
resistor. The compact resistor is not supplied with the drive and can be purchased separately, refer to section 2.8
Installation and system accessories
on page 14.
Side by side mounting is still permissible with compact braking resistor fitted.
Table 4-10 provides the compact braking resistor data.
The compact resistor is suitable for applications with a low level of regenerative energy only.
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
Drive voltage rating
DC bus voltage level
200 V
390 V
400 V
780 V
High temperatures
Braking resistors can reach high temperatures. Locate braking resistors so that damage cannot result. Use cable having insulation capable
of withstanding high temperatures.
NOTE
WARNING
NOTE
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