Learn about manual star delta starter circuit diagram. Difference between star connection and delta connection motor.
Star and delta motor connection
We all know or have heard of star-delta starter circuits. The purpose of using this circuit is to reduce the starting current of a three-phase motor. The figure below shows how to connect the motor in star and delta modes.
Star and delta motor connection (source: Electrical Technician)
a. Star connection:
In a Star Connection, the 3 phase wires connect to a common point or star point; Neutral is taken from this common point. Due to its shape, the star connection is sometimes also called as Y or Wye connection.
If only the three phase wires are used, then it is called 3 Phase 3 Wire system. If the Neutral point is also used (which often it is), it is called 3 Phase 4 Wire system. The following image shows a typical Star Connection.
Star connection
In Star system of interconnection, the starting ends or finishing ends (similar ends) of three coils are connected together to form the neutral point. Star Connection is obtained by connecting together similar ends of the three coils, either “Starting” or “Finishing.” The other ends are joined to the line wires. The common point is called the neutral or Star Point, which is represented by N.
b. Delta connection
In Delta Connection, there are only three wires for distribution; all the three wires are phases (no neutral in a Delta connection). Delta connection is the most preferred system for AC power transmission, while for distribution Star connection is usually used.
Delta connection
In the Delta (also denoted by Δ) system of interconnection, the starting ends of the three phases or coils are connected to the finishing ends of the coil. In Delta connection, the three windings interconnection looks like a short circuit, but this is not true.
Principle of manual star delta starter circuit diagram
Manual star delta starter circuit diagram
+ The ON1 and OFF push button controls the motor to operate in star mode.
+ The ON2 and OFF push button controls the motor to operate in delta mode.
+ When we press ON1 button, the coil of contactor K1 will be energized. At this time, the contacts of contactor K1 change state. The contact of contactor K1 closed will supply power to the coil of contactor K. So now in the dynamic circuit: the main contacts of contactor K and K1 are closed, and the motor operates in star mode.
Motor is operating in star connection mode
+ After the motor speed reaches nearly 75% of the rated motor speed, the operator will press the OFF button and then press ON2. At this time, the main contact of contactor K1 is open. The main contacts of contactors K and K2 are closed. The motor operates in delta connection mode.
Motor is operating in delta connection mode
+ The normally closed contacts of contactors K1 and K2 are interlocks; this means the motor can only be connected in star or delta mode at a time.
Simulation video
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