Star-Delta Motor Starter Power and Control Starter Circuit Diagram

Star – Delta motor starters are perhaps one of the most popular types of starters. They are used to reduce the starting current of motors.

Basics of Starters

Induction motors often draw about 10 times full load current at the time of starting. While we can easily switch on the small motors by using DOL (Direct on-line) connections, doing so on large-sized motors is menacing and it results in serious damages to the motor. A star – delta motor starter reduces this starting current to a lower acceptable level and it contains three contactors namely the:
  1. Main
  2. Delta
  3. Star
There are four states of contactors:
  1. Open state: In this condition, the main contactor is closed and other two are open. At this condition, the voltage exists at one end of windings, but the other end is open and no current passes through. Such condition results in a spinning rotor and on that point a motor behaves as a generator.
  2. Star state: The star and main are closed in this condition. The motor produces 1/3rd of direct on line torque and current.
  3. Delta state: The Delta and main contactors are closed. In this condition full line torque and power flow through.
  4. Open state: In this condition all contactors are open.
The little basics provided above are quite enough to have a basic overview. Let’s roll towards the wiring diagram.

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