ABB ACS850 series, Application Manual

Page: 32 / 39

32
•
The resistance
R
br(i)
of each individual braking resistor must be at least
R
br,min
according to the braking chopper data of the drive module in question.
•
The resistance value
R
br(i)
of each individual braking resistor should also fulfil the
peak braking power requirements. In the following calculations, the value of
U
dc
is
840 V DC.
•
( )
max , gen
max , br max , br
) i max( , br
dc
) i (
br ) i min(
P
...) P P (
P
U
R R
×
+ +
< <
2 1
2
Where
P
br,max(i)
is the braking power rating of the concerned braking chopper.
•
The selected braking resistors should be able to handle the braking energy
generated in fast dynamic situations (time is just a few seconds).
•
) i ( R gen
cont , br cont , br
) i ( cont , br
E dt P
...) P P (
P
< ×
+ +
∫
2 1
Where
E
R(i)
is the energy pulse rating of the individual resistor and
P
br,cont(i)
is the power
rating of the concerned individual braking chopper.
•
The nominal power rating of the resistor must be adequate for the average
regenerative power.
•
) i ( R , N ave , gen
cont , br cont , br
) i ( cont , br
P P
...) P P (
P
< ×
+ +
2 1
Where
P
N,R(i)
is the nominal power rating of the individual resistor (steady state
continuous load). For more detailed analysis and more optimum selection, the pulse
load curves of the selected resistor should be studied.
Braking resistor types
Resistor types JBR-xx and SAFUR for dynamic load cycles are available for the drive
modules. See the relevant hardware manual for detailed data.
General system design items
Fuse protection
Fuses are needed on the AC supply side and in the DC connections. These provide
protection for the cabling and also limit the damages in case there is a short circuit in
the system. The following items should be checked for fuse selection:
•
fuse class depending on the fault current type and protected items
•
fuse voltage rating
•
fuse current rating
•
standards and regulations. The general guidelines for the fuse selection are given
here. Take always also the local and application specific regulations into account.
Common DC configurations