3 Point Starter

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3 Point Starter (Tree Point Starter)

A three-point starter is an electrical device used to start, control, and protect the speed of direct current (DC) motors. It is commonly used in applications where the motor requires a gradual increase in voltage and current during startup to prevent excessive current flow and damage to the motor windings.


The three-point starter consists of three main components: the main contacts, the field regulator, and the armature contacts. Here's how it works:


1. Main Contacts: The main contacts are responsible for connecting the motor to the power source. They are usually controlled by a switch or a lever. In the starting position, the main contacts are open, preventing the flow of current to the motor.


2. Field Regulator: The field regulator controls the excitation of the motor's field windings. It is typically a variable resistor or a rheostat that adjusts the field current. The field windings are connected in series with the armature windings and determine the motor's speed. By controlling the field current, the field regulator can vary the speed of the motor.


3. Armature Contacts: The armature contacts are also controlled by a switch or a lever. When the main contacts are closed, and the armature contacts are in the starting position, the armature windings are connected to a resistance called the starting resistance. This resistance limits the amount of current flowing through the armature during startup, preventing damage.


The starting process involves the following steps:


1. Open the main contacts to ensure that no current flows to the motor.

2. Adjust the field regulator to set the desired field current.

3. Close the armature contacts in the starting position to connect the armature windings to the starting resistance.

4. Close the main contacts to supply power to the motor.

5. Gradually reduce the starting resistance to increase the voltage and current supplied to the motor. This gradual increase in voltage prevents excessive current flow during startup.

6. Once the motor reaches the desired speed, the armature contacts are moved to the running position, bypassing the starting resistance and directly connecting the armature windings to the power source.

7. The field regulator can be adjusted during operation to control the motor's speed.


In summary, a three-point starter provides a controlled and gradual startup for DC motors, protecting them from excessive current and allowing for speed control.

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