Polyphase Induction Motors

Figure 1: A typical three phase motor.

                                                     

Why does a 3 phase AC induction motor have to be connected in star delta (or wye delta) configuration - What is the significance and advantage of using star and delta in motor connection

Three phase AC induction motors are known to have a very high start-up surge current. The most practical approach to reduce the high start-up inrush current is by firstly implementing a star (or wye) configuration to the motor's 6 leads wiring terminal during the start-up run of the motor. When the motor slowly picks up speed and a significant decrease in the amount of current is achieved then the motor's 6 leads wiring terminal is then reconfigured to a delta connection.

Star Delta or Wye Delta Industrial Process Automation Control Motor Wiring Configuration - Recommended wiring configuration suitable for reduced changeover current peaks from star to delta motor connection - A basic How To Learn Guide

Fig-1

With reference to our previous articles which covered the star delta or wye delta motor wiring configuration - the delta motor wiring diagram presented in Fig-1 on the right shows two of each of the six motor terminals joined together and while connected also to each of the three reference source voltages that conforms to an orderly configuration of phase sequence U1-V2-L1, V1-W2-L2, W1-U2-L3.

Star Delta or Wye Delta Motor Wiring Configuration - A basic how to guide

The previous article which covered the star delta motor control power circuit for industrial process control presented an electrical diagram showing the interchanging motor wiring configuration for a star connection and a delta connection using magnetic contactors as motor starters. Exploring further with reference to the previous star delta power circuit diagram, if you manually trace each line connections going to the motor you will begin to understand how the following star and delta motor wiring connections are achieved.