SAF OP-STOP DCI User Manual
Page 7
OP-STOP DC INJECTION BRAKE
Page 2
1.2 APPLICATION NOTES
The motor torque/speed characteristic of an induction motor under DC supply is similar to the
normal curve published for constant frequency, at 50 or 60 Hz, but this time having
"synchronous speed" zero RPM. This is illustrated below.
For smooth braking the DC current is typically adjusted to 300% of the motor nameplate
current. The stopping time depends on the torque setting and also the inertia of the mechanical
system.
Electric braking is not recommended for continuous or repetitive operation. The kinetic energy
of the mechanical system is transformed into heat during braking ( energy conservation ). That
heat is dissipated in the rotor of the motor.
On wound rotor motors the external rotor resistance will absorb most of the energy. On squirrel
cage motors, overheating of the motor is a real danger if frequent operation is used.
Keeping DC current on the motor stator for a short time after the motor has stopped is quite
acceptable. The heat produced by the I2R losses are not significant, and they are dissipated in
the stator only, not in the rotor where the rotational energy is dissipated.
TORQUE
SPEED
0=N
S
100%