ABB ACS880-04 drive modules, Application Manual

Page: 29 / 48

Planning – basics 29
Brake resistor selection formulas - system with several brake choppers and
resistors
Use these formulas to select the brake resistor for each chopper, and to verify the resistor
selection:
R
br(i)
> R
br,min(i)
E
r(i)
Energy pulse that individual brake resistor i can withstand and dissipate during one load
cycle. See the drive hardware manual (ABB brake resistors) or resistor data sheet.
R
br(i)
Resistance of individual brake resistor i. See the drive hardware manual (ABB brake
resistors) or resistor data sheet.
R
br,min(i)
Minimum resistance of brake resistor i that you can use with individual drive (brake
chopper). See the drive hardware manual.
P
br,cont(i)
Continuous braking power of individual brake chopper. See the drive hardware manual
(ABB brake resistors) or resistor data sheet.
P
g1
Generating power of the common DC link during time t
g1
. See the graph in section Defining
the energy absorbing capacity of the common DC link on page 26 .
P
gen
(t) Generating power of the common DC link as a function of time over one duty cycle.
P
gen,max
Maximum generating power of the common DC link.
P
N,r(i)
Nominal power of individual brake resistor i. See the drive hardware manual (ABB brake
resistors) or resistor data sheet.
P
br,contr(i)
Continuous power of brake chopper supplying the individual brake resistor i. See section
Brake chopper power ratings on page 44 .
P
br,max(i)
Maximum power of brake chopper supplying the individual brake resistor i. See section
Brake chopper power ratings on page 44 .
t
g1
Duration for generating power P
g1
. See graph in section Defining the energy absorbing
capacity of the common DC link on page 22 .
U
ac
AC power line voltage
U
dc,h
= 2.1 × U
ac
High DC link voltage value but clearly below the trip level
max ,
2 max , 1 max ,
2
) ( )
...) (
) max( ,
gen
br br
dc
i br i
P
P P
i Pbr
U
R
×
+ +
< <
( )
) (
2 , 1 ,
) ( ,
...
i R gen
cont br cont br
i cont br
E dt P
P P
P
< ×
+ +

( )
) ( , ,
2 , 1 ,
) ( ,
...
i R N ave gen
cont br cont br
i cont br
P P
P P
P
< ×
+ +