Darect on line statar
They may include only the means for starting and stopping the motor or they may include other functions.
An electric motor controller can be classified by the type of motor it is to drive such as permanent magnet, servo, series, separately excited, and alternating current.
A larger motor requires a specialized switching unit called a motor starter or motor contactor.
When energized, a direct on line (DOL) starter immediately connects the motor terminals directly to the power supply.
The maximum size of a motor allowed on a direct on line starter may be limited by the supply utility for this reason.
By using an autotransformer or a series inductance, a lower voltage is present at the motor terminals, reducing starting torque and inrush current.
Once the motor has come up to some fraction of its full-load speed, the starter switches to full voltage at the motor terminals.
Very large motors running on medium voltage power supplies (thousands of volts) may use power circuit breakers as switching elements.
A direct on line (DOL) or across the line starter applies the full line voltage to the motor terminals, the starters or cubicle locations, can usually be found on an ELO drawing. A DOL motor starter also contains protection devices, and in some cases, condition monitoring.
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For example, a numerically controlled lathe will accurately position the cutting tool according to a preprogrammed profile and compensate for varying load conditions and perturbing forces to maintain tool position.