Diagnostics Optimization CT MODBUS RTU Technical Data
94
E300 Design Guide
Issue Number: 1
4.14 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 4-17 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
(
D19
)
and
Braking IGBT
(
D20
) upper threshold.
Table 4-17 Default braking transistor turn on voltage
The drive software contains an overload protection function for a braking resistor. In order to enable and set-up this function, it is necessary to enter
three values into the drive:
•
Braking Resistor Rated Power
(
D15
)
•
Braking Resistor Thermal Time Constant (
D16
)
•
Braking Resistor Resistance
(
D18
)
This data should be obtained from the manufacturer of the braking resistors.
Braking Resistor Thermal Accumulator
(
D17
) gives an indication of braking resistor temperature based on a simple thermal model. Zero indicates the
resistor is close to ambient and 100 % is the maximum temperature the resistor can withstand. A ‘Brake Resistor’ alarm is given if this parameter is
above 75 % and the braking IGBT is active. A Brake R Too Hot trip will occur if
Braking Resistor Thermal Accumulator
(
D17
) reaches 100 %, when
Action On Trip Detection
(
H45
) is set to 0 default value) or 1.
If
Action On Trip Detection
(
H45
) is equal to 2 or 3, a Brake R Too Hot trip will not occur when
Braking Resistor Thermal Accumulator
(
D17
) reaches
100 %, but instead the braking IGBT will be disabled until
Braking Resistor Thermal Accumulator
(
D17
) falls below 95 %. This option is intended for
applications with parallel connected DC buses where there are several braking resistors, each of which cannot withstand full DC bus voltage
continuously. With this type of application, it is unlikely the braking energy will be shared equally between the resistors because of voltage
measurement tolerances within the individual drives. Therefore with
Action On Trip Detection
(
H45
) set to 2 or 3, then as soon as a resistor has
reached its maximum temperature the drive will disable the braking IGBT, and another resistor on another drive will take up the braking energy. Once
Braking Resistor Thermal Accumulator
(
D17
) has fallen below 95 % the drive will allow the braking IGBT to operate again.
This software overload protection should be used in addition to an external overload protection device.
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 4.17.3
on page 100 for further details. Internal connection does not require the
cable to be armored or shielded.
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.
Braking resistor overload protection parameter settings. Failure to observe the following information may
damage the resistor.
The drive software contains an overload protection function for a braking resistor.
WARNING
CAUTION
Parameter
Detail
Braking Resistor Rated Power
(
D15
)
Power units in kW and if the rated power is set to zero this protection is disabled
Braking Resistor Thermal Time Constant
(
D16
)
The thermal time constant of the resistor can be calculated from the single pulse
energy rating (E) and continuous power rating (P) of the resistor. Thermal time
constant =
τ
= E / P
Braking Resistor Resistance
(
D18
)
Braking resistor resistance in ohms
Summary of Contents for 03200106
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