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,
2max,1max,
2
)()
...)(
)max(,
gen
brbr
dc
ibri
P
PP
iPbr
U
R
×
++
<<
()
)(
2,1,
)(,
...
iRgen
contbrcontbr
icontbr
EdtP
PP
P
<×
++
()
)(,,
2,1,
)(,
...
iRNavegen
contbrcontbr
icontbr
PP
PP
P
<×
++
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