66
Unidrive M Modular Installation Guide
Issue Number: 2
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.
6.8 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 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 6-17 shows the DC voltage level at which the drive turns on the
braking transistor.
Table 6-17 Braking transistor turn on voltage
N
When a braking resistor is used, Pr
00.015
should be set to FASt ramp
mode.
6.8.1 External braking resistor
When a braking resistor is to be mounted outside the enclosure, ensure
that it is mounted in a ventilated metal housing that will perform the
following functions:
•
Prevent inadvertent contact with the resistor
•
Allow adequate ventilation for the resistor
When compliance with EMC emission standards is required, external
connection requires the cable to be armored or shielded, since it is not
fully contained in a metal enclosure. See section 6.10.4
on page 72 for further details.
Internal connection does not require the cable to be armored or
shielded.
Minimum resistances and power ratings
Table 6-18 Minimum resistance values and peak power rating for
the braking resistor at 40°C (104°F)
* Resistor tolerance: ±10 %
** Continuous rating if drive is part of a common DC bus system. In
parallel systems without the DC bus connected, the resistors must be
matched to within ±5 %.
For high-inertia loads or under continuous braking, the
continuous
power
dissipated in the braking resistor may be as high as the power rating of
the drive. The total
energy
dissipated in the braking resistor is dependent
on the amount of energy to be extracted from the load.
The instantaneous power rating refers to the short-term maximum power
dissipated during the
on
intervals of the pulse width modulated braking
control cycle. The braking resistor must be able to withstand this
dissipation for short intervals (milliseconds). Higher resistance values
require proportionately lower instantaneous power ratings.
In most applications, braking occurs only occasionally. This allows the
continuous power rating of the braking resistor to be much lower than
the power rating of the drive. It is essential, though, that the
instantaneous power rating and energy rating of the braking resistor are
sufficient for the most extreme braking duty that is likely to be
encountered.
Optimization of the braking resistor requires a careful consideration of
the braking duty.
Select a value of resistance for the braking resistor that is not less than
the specified minimum resistance. Larger resistance values may give a
cost saving, as well as a safety benefit in the event of a fault in the
braking system. Braking capability will then be reduced, which could
cause the drive to trip during braking if the value chosen is too large.
Drive voltage rating
DC bus voltage level
200 V
390 V
400 V
780 V
575 V
930 V
690 V
1120 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.
Overload protection
When an external braking resistor is used, it is essential that
an overload protection device is incorporated in the braking
resistor circuit; this is described in Figure 6-12 on page 67.
NOTE
WARNING
WARNING
Model
Minimum
resistance*
Ω
Instantaneous
power rating**
kW
Continuous
power rating
kW
09201760
1.2
144.5
59.4
09202190
1.2
144.5
79.7
10202830
1.3
130
98.6
10203000
1.5
130
116.7
09402000
2.4
282.9
118.6
09402240
2.4
282.9
156.9
10402700
2.6
260.0
198.2
10403200
2.8
260.0
237.6
09501040
3.3
291.3
97.7
09501310
3.3
291.3
116.7
10501520
3.3
291.3
155.6
10501900
2.5
384.4
155.6
09101040
4.2
331.9
116.3
09601310
4.2
331.9
139.1
10601500
4.2
331.9
166.7
10601780
3.3
422.4
193.0
Summary of Contents for 09201760D
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