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Altivar
®
58 TRX AC Drives
Dynamic Braking Resistor Kits
© 2000–2003 Schneider Electric All Rights Reserved
36
09/2003
DB resistor requirements:
Peak braking power required to develop braking torque (T
b
) when decelerating from a given speed
P
i
= T
b
x N
base
/(7.04) = (1.97 x 1740)/(7.04) = 487 W
The braking power that must be absorbed for a time (td) during stopping or speed changing
operation: P
d
= 0.5 x P
i
= 0.5 x 487 = 243 W for a period of t
d
seconds
The average braking power that must be dissipated during a machine cycle:
P
a
= P
d
x t
d
/t
c
= 243 x 5/30 = 40.5 W
Capability of VW3A66711 DB resistor assembly for ATV58U72N4 controller:
Peak braking power that can be developed with VW3A66711 DB resistor assembly with controller
configured for 460 Vac input line operation: P
i
= (V
db
)
2
/R
db
= (850 V)
2
/120 Ω = 6020 W
The braking power that can be absorbed for t
d
(based on DB resistor hot state current-time
characteristic curve shown on page 37):
P
d
= R
db
x ((Multiple of I
r
at t
d
) x Ir)
2
= 120Ω x (3.5 x 1.0)
2
= 1470 W
Since R
db
limits the peak current that can be drawn from the drive controller DC bus, the value of
[(Multiple of I
r
) x I
r
] must be limited to no greater than (√ p
i
/R
db
).
The average braking power that can be dissipated continuously:
P
a
= R
db
x (I
r
)
2
= 120 Ω x (1)
2
= 120 W
For this example, the VW3A66711 DB resistor assembly will work as intended for the application.