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1 DESCRIPTION
1.1 OVERVIEW
The TRU-START DC Injection braking units provide smooth braking for AC induction
motor. 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 TRU-START solid state starter, or as stand
alone units for new or retrofit installations.
Cutler-Hammer TRU-START DC Injection 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 TRU-START DC Injection brake
unit will neverwear 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. Cutler-Hamer 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.
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