Braking; Figure 4-13 Alternative Connection For Multiple Motors; Table 4-10 Braking Transistor Turn On Voltage - Emerson unidrive sp User Manual
Universal variable speed ac drive for induction and servo motors model sizes 0 to 6
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Figure 4-13 Alternative connection for multiple motors
/ Δ motor operation
4.8.5
and Δ connections of the motor should always
The voltage rating for
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.
400V drive 400V rated voltage
200V drive 200V rated voltage
A typical 3 phase motor would be connected in
Δ for 200V operation, however, variations on this are common e.g.
690V Δ 400V
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.
4.8.6
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
WARNING
speed.
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 (T31) when opened provides a SAFE
TORQUE OFF function. This can in many cases replace output
contactors.
For further information see section 4.16 SAFE TORQUE OFF on
page 99.
78
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parameters
Motor protection
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4.9
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 4-10 shows the DC voltage level at which the drive turns on the
braking transistor.
Table 4-10 Braking transistor turn on voltage
Drive voltage rating
200V
400V
575V
690V
N
NOTE
When a braking resistor is used, Pr 0.15 should be set to FASt ramp
mode.
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.
WARNING
4.9.1
Heatsink mounted braking resistor
A resistor has been especially designed to be mounted internal to the
drive (size 0) or within the heatsink of the drive (sizes 1 and 2). See
section 3.11 Internal / heatsink mounted braking resistor on page 60 for
mounting details. The design of the resistor is such that no thermal
protection circuit is required, as the device will fail safely under fault
conditions. On sizes 0, 1 and 2, the in built software overload protection
is set up at default for the designated heatsink mounted resistor. Table 4-
11 provides the resistor data for each drive rating.
The internal braking resistor for size 0 is installed with a
thermistor which must be connected to the drive whenever
the internal braking resistor in installed.
CAUTION
N
NOTE
The internal/heatsink mounted resistor is suitable for applications with a
low level of regen energy only. See Table 4-11.
Onboard
Advanced
Technical
Diagnostics
PLC
parameters
Data
DC bus voltage level
390V
780V
930V
1120V
Unidrive SP User Guide
Issue Number: 13
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