Circuit Protection - Allen-Bradley Ultra1500 2092-DA1 User Manual

5-24 Ultra1500 Application Examples
Publication 2092-UM001D-EN-P — July 2005

Circuit Protection

The Ultra1500 will not allow the drive to be enabled if the motor
characteristics are such that the dynamic braking circuitry could be damaged in
the event of a stop. (Even if the Fault and Disable Braking parameter of the
drive is set to Free Stop, a loss of control power will also activate the dynamic
braking circuitry.)
The Ultra1500 dynamic braking circuitry was
ATTENTION
designed to operate with the TL-Series motor family
with reasonable load inertias and stopping
!
frequencies. If your application requires high load
inertias (greater than 10:1) and/or stopping
frequencies greater than once every 5 minutes,
consult your Allen-Bradley representative before
using the internal dynamic brake circuitry.
The current required to stop the motor is dependent on several motor
characteristics such as speed, inductance, resistance, and back-EMF constant.
The drive uses the following formula to determine if the stopping current will
exceed the circuit ratings:
[ ⋅
2 I
where:
I
= intermittent current rating of the drive in Amps (0–peak)
Peak
K = phase-neutral back-EMF constant of the motor in Volts/rpm or
E
Volts/m/s (0–peak)
V = maximum speed of the motor in rpm or m/s
Max
R = motor phase-neutral resistance in Ohms
L = motor phase-neutral inductance in Henries
ω
= maximum electrical frequency of the motor in radians/second.
E
⋅
K V
2
E Max
] <
----------------------------------
Peak
2
[ ω
R +
E
2
2
]
L