Planning – basics 27
Defining the maximum DC link voltage
The table below shows how you can define the maximum DC link voltage U
dc,lim
. See
section DC voltage limits of the drive on page 45 for the explanation of the symbols.
1)
Parameter 30.30 Overvoltage control in the ACS880 primary control program.
2)
You must have some margin to the limit to avoid fault trips.
3)
The resistor braking starts when the voltage exceeds the limit.
Selecting the brake choppers and resistors
You must use brake choppers and resistors in the common DC system if the DC link
capacitors cannot absorb the surplus energy, and there is no regenerative drive in the
system.
Depending on the drive frame size, the brake chopper is either a standard or optional
device. See section Brake chopper types on page 15. If the chopper is available as an
option, you can order it from ABB as factory-installed.
You must acquire and install the brake resistors separately. See the drive hardware
manual for ABB brake resistors for each drive. Use can use either the default ABB brake
resistors defined for each drive or other resistors that meet the selection criteria.
Select the choppers and resistors as follows:
1. Select the choppers:
• Examine if the chopper load capacity of the drive with the highest power rating is
high enough for the surplus power of the common DC link. See section Brake
chopper selection formulas on page 28.
• If the chopper load capacity of one drive is not enough, use also the chopper with
the second highest power rating, etc. until the total load capacity meets the
criteria.
2. Select the brake resistors:
• If you plan to use one chopper and resistor only, either verify the default ABB
brake resistor selection, or select a user-defined resistor. See section Brake
resistor selection formulas - system with one brake chopper on page 28. If the
resistor does not meet the criteria, try another resistor, or take the next biggest
chopper and its resistor in use as well.
• If you plan to use several choppers and resistors, verify each resistor selection.
See section Brake resistor selection formulas - system with several brake
choppers and resistors on page 29. If a resistor does not meet the criteria, try
another resistor, or take the next biggest chopper and its resistor in use as well.
Repeat the verification until each resistor meets the criteria.
Overvoltage control
1)
Brake choppers and
resistors
U
dc,lim
Enabled Not in use U
dc,lim
= U
DC,ovc
Disabled Not in use
U
dc,lim
< U
DC,ovt
2)
Disabled In use
U
dc,lim
= U
DC,brcl
3)
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