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All motors must have a control device to start and stop the motor called a “motor controller”. |
Motor Controller |
A motor controller is the actual device that energizes and de-energizes the circuit to the motor so that it can start and stop. |
• Motor controllers may include some or all of the following motor control functions: |
S starting, stopping, over-current protection, overload protection, reversing, speed |
changing, jogging, plugging, sequence control, and pilot light indication. |
S Controllers range from simple to complex and can provide control for one motor, |
groups of motors, or auxiliary equipment such as brakes, clutches, solenoids, heaters, or other signals. |
Motor Starter |
The starting mechanism that energizes the circuit to an induction motor is called the “starter” and must supply the motor with sufficient current to provide adequate starting torque under worst case line voltage and load conditions when the motor is energized. |
• There are several different types of equipment suitable for use as “motor starters” but only |
two types of starting methods for induction motors: |
1. Across the Line Starting 2. Reduced Voltage Starting |
Across the Line Starting of Motors |
Across the Line starting connects the motor windings/terminals directly to the circuit voltage “across the line” for a “full voltage start”. |
• This is the simplest method of starting a |
motor. (And usually the least expensive). |
• Motors connected across the line are capable |
of drawing full in-rush current and developing maximum starting torque to accelerate the load to speed in the shortest possible time. |
• All NEMA induction motors up to 200 |
horsepower, and many larger ones, can withstand full voltage starts. (The electric distribution system or processing operation may not though, even if the motor will). |