Altivar 31 - Square D

Altivar ® 31 Adjustable Speed AC Drives
Dynamic Braking Resistor Kits
DB resistor requirements:
Peak braking power required to develop braking torque (Tb) when decelerating from a given 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 (t d) during a stop or speed change 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 ATV31HU40N4 controller:
Peak braking power that can be developed with the VW3A66711 DB resistor assembly with the
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 the DB resistor hot state current-time
characteristic curve shown below):
P d = R db x [(Multiple of I r at t d) x Ir] 2 = 120 Ω 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.
Current/time characteristics for DB resistor assemblies
The figure below shows the allowable trip times 1 as a function of current setting multiples with the
dynamic braking resistor assembly located in a 40 °C (104 °F) ambient temperature environment. See
“Calculating resistor size” on page 14 for an example of how to calculate resistor size.
Time (s)
10000
1000
100
10
1
0.1
0.01
Hot State
0.001
1 1.5 10
Multiples of Current Setting (lr)
100
1. Of the GV2 manual starter; see page 16.
Cold State
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DynBrkCurves.eps
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