Direct on line starter

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A direct on line starter, often abbreviated DOL starter, is a widely-used starting method of electric motors. The term is used in electrical engineering and associated with electric motors. There are many types of motor starters, the simplest of which is the DOL starter.

Contents 1 Definition 2 DOL Reversing Starter 3 Example of Motor Starters 4 Motor direction reversal 5 See also 6 External links

[edit] Definition

A motor starter is an electrical/electronic circuit composed of electro-mechanical and electronic devices which are employed to start and stop an electric motor. Regardless of the motor type (AC or DC), the types of starters differ depending on the method of starting the motor. A DOL starter connects the motor terminals directly to the power supply. Hence, the motor is subjected to the full voltage of the power supply. Consequently, high starting current flows through the motor. This type of starting is suitable for small motors below 5 hp (3.75 kW). Reduced-voltage starters are employed with motors above 5 hp. Although DOL motor starters are available for motors less than 150 kW on 400 V and for motors less than 1 MW on 6.6 kV. Supply reliability and reserve power generation dectates the use of reduced voltage or not

[edit] DOL Reversing Starter

Most motors are reversible or, in other words, they can be run clockwise and anti-clockwise. A reversing starter is an electrical or electronic circuit that reverses the direction of a motor automatically. Logically, the circuit is composed of two DOL circuits; one for clockwise operation and the other for anti-clockwise operation.

[edit] Example of Motor Starters

A very well-known motor starter is the DOL Starter of a 3-Phase Squirrel-Cage Motor. This starter is sometimes used to start water pumps, compressors, fans and conveyor belts. With a 400V, 50 Hz, 3-phase supply, the power circuit connects the motor to 400V. Consequently, the starting current may reach 3-8 times the normal current. The control circuit is typically run at 24V with the aid of a 400V/24V transformer.

[edit] Motor direction reversal

Changing the direction of a 3-Phase Squirrel-Cage Motor requires swapping any two phases. This could be achieved by a contactor KM1 swapping phase L2 and L3 between the supply and the motor.

[edit] See also

• Motor Soft Starter
• Adjustable-speed drive
• Variable-frequency drive
• Thyristor drive

v • d • e Electric motors Broad Motor Categories Synchronous motor • AC motor • DC motor Conventional Electric Motors Induction • Brushed DC • Brushless DC • Stepper • Linear • Unipolar • Reluctance Novel Electric Motors Ball bearing • Homopolar • Piezoelectric • Ultrasonic • Electrostatic Motor Controllers Adjustable-speed drive • Amplidyne • Direct Torque Control • Direct on line starter • Electronic speed control • Metadyne • Motor controller • Variable-frequency drive • Ward Leonard control See also Barlow's Wheel • Nanomotor • Traction motor • Lynch motor • Mendocino motor • Repulsion motor • Inchworm motor • Booster (electric power) • Brush (electric)

[edit] External links

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