SAF OP-STOP DCI - Manual (Page 6)

OP-STOP DC INJECTION BRAKE
Page 1
1 DESCRIPTION
1.1 OVERVIEW
The OP-STOP braking units provide smooth braking for AC induction motors. The brake units
offer adjustable braking because they are current controlled. Unlike a mechanical brake, an
electrical brake will never wear out. The brake operates by injecting DC current in two phases
of the motor to rapidly decelerate it to zero speed.
These units can be supplied as an option to the OPAL solid state starter, or as stand alone units
for new or retrofit installations.
SAF's OP-STOP braking modules offer a unique combination of features that make it very
reliable, easy to use, and energy efficient. These features include:
• Closed Loop Current Regulation:
The brake, operating with a closed loop current regulator, provides consistent torque
every time. This torque is independent of line voltage variations.
• Direct Power Connection:
The brake's power input is connected directly to the AC line, and the power output is
connected directly to the motor, no contactors are required. The unit adapts itself to any
input voltage between 200 and 600 VAC with no adjustments required.
• Efficient Power Circuit:
The power circuit is an efficient four Silicon Controlled Rectifier ( SCR ) configuration
which uses some of the SCR's as a "free wheeling diode", thus maximizing the DC
current through the motor coils generated by the AC input current.
With every benefit there is usually a trade-off. Although the OP-STOP brake unit will never
wear out like a mechanical brake, the trade-off is that should there be a loss of power, the brake
unit will not operate without battery back-up. SAF can supply a reliable battery back-up to
overcome this disadvantage.
Braking is initiated when the motor starter is opened and the voltage across the motor has
dropped to below 30% or 80% of the line supply. DC injection is removed after an adjustable
period has elapsed. It does not provide zero speed sensing, although a normally closed contact
from a zero speed switch may be connected to the Disable Input.
If braking is released before the motor stops, the motor will coast to rest. If the braking remains
on after the motor stops, the DC supply will provide a holding brake.