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 develo p braking tor que (Tb) wh en decelerati ng from a giv en speed
Pi = Tb x Nbase/(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: Pd = 0.5 x Pi = 0.5 x 487 = 243 W for a period of td seconds
The average braking power that must be dissipated during a machine cycle:
Pa = Pd x td/tc = 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 assemb ly with controll er
configured for 460 Vac input line operation: Pi = (Vdb)2/Rdb = (850 V)2/120 Ω = 6020 W
The braking power that can be absorbed for td (based on DB resistor hot state current-time
characteristic curve shown on page 37):
Pd = Rdb x ((Multiple of Ir at td) x Ir)2 = 120Ω x (3.5 x 1.0)2 = 1470 W
Since Rdb limits the peak current that can be drawn from the drive controller DC bus , th e v alue of
[(Multiple of Ir) x Ir] must be limited to no greater than (√ pi/Rdb).
The average braking power that can be dissipated continuously:
Pa = Rdb x (Ir)2 = 120 Ω x (1)2 = 120 W
For this example, the VW3A66711 DB resistor assembly will work as intended for the application.