on video Star delta Starter Connection Diagram

A Star-Delta starter is an electromechanical device used to start and control the speed of a three-phase induction motor. This starter employs the star-delta (Y-Δ) method for starting the motor, which involves changing the motor’s winding connection from a Star configuration to a Delta configuration once the motor reaches a certain speed.

The Star-Delta starter includes a control circuit that typically consists of a timer, contactors, and overload relays. When the motor is started, it is initially connected in a Star configuration to reduce the starting current, which can be up to 6 times the motor’s full-load current. After the motor reaches a specific speed, the timer switches the winding connection to a Delta configuration to ensure the motor operates efficiently.

This starter is widely used in industries where high-power motors are required, such as in oil and gas, mining, and manufacturing. The star/delta starter offers several advantages, including reduced starting current, better control of inrush current, and reduced stress on the motor windings during starting. However, it also has some disadvantages, including increased cost and complexity, longer starting time, and reduced torque during starting.

In this tutorial, we will demonstrate the automatic star-delta (Y-Δ) starting method for 3-phase AC induction motors. This will include providing a schematic, power and control, PLC ladder, and wiring diagrams. We will also explain how the star-delta starter works and discuss its applications, as well as its advantages and disadvantages.

On the left-hand side, there is the main contactor with a pneumatic timer. The main contactor is always energized.

In the middle, there is the Delta contactor, which is equipped with a thermal overload for motor protection in the event that the motor exceeds the ampere rating set on the thermal overload.

The phase current flows from L1 to the thermal overload contact through an MCB/MCCB or general fuse, then to the OFF push button, On push button interlocking contact 2, and then to K3. The circuit is thus completed, and both contactor coil C3 and timer coil (T) are energized simultaneously. As a result, the motor winding is connected in Star, and when K3 is energized, its auxiliary open links will close, and the close links will open.

Consequently, Contactor K1 is also energized, and the Three Phase Supply reaches the motor. Since the winding is connected in Star, each phase will receive √3 times less than the line voltage, which ensures safe motor starting. The close contact of K3 in the Delta line opens, preventing the activation of contactor 2 (K2).After the push button is released, Timer coil and coil 3 will receive a supply through Timer contact (Ia), Holding contact 3, and the close contact 2 of K2. When Contactor 1 (K1) is energized, the two open contacts in the line of K1 and K2 will close.

For a specific time (generally 5-10 seconds), the motor will be connected in Star. After that, the Timer contact (T) will open (which can be adjusted by rotating the timer knob to set the time again), and as a result, Contactor 3 (K3) will turn off, and the open link of K3 (in the line of K2) will close, causing K2 to energize. When K3 is off, the star connection of the winding will also open, and K2 will close, connecting the motor winding in Delta. Contact 2 (which is in the line K3) will also open, preventing the activation of coil 3 (K3).

Now that the motor is connected in Delta, each phase will receive full line voltage (415V), and the motor will start to run at full speed.

L1 , L2, L3 = Brown, Black, Blue ( 3 Phase Lines)

CB / MCB / MCCB = General Circuit Breaker

Main = Main Supply

Y = Star

Δ = Delta

T = Timer

K1, K2, K3 = Contactors

O/L = Thermal Overload Relay

NO = Normally Open

NC = Normally Closed

K1/NO = Contactor Holding Coil (Normally Open)

Advantages & Disadvantages

Advantages:

Simple design and operation.

Comparatively cheaper than other voltage controlling methods.

The torque and current performance of the Y-Δ starter is good.

It draws two times the starting current of the FLA (Full Load Ampere) of the connected motor.

It reduces the starting current to approximately one-third compared to a DOL (Direct ON Line Starter).

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Starting Torque is also reduced to one-third because the starter reduces the starting current to one-third of the rated current [as Line voltage is also reduced to 57% (1/√3)].

It requires six leads or terminals for a Delta-connected motor.

For Delta connection, the supply voltage must be the same as the rated motor voltage.

At switching time (from Star to Delta), if the motor does not reach at least 90% of its rated speed, then the current peak may be equally high as in a Direct ON Line starter( D.O.L), thus causing harmful effects on the contactor’s contacts, making it unreliable.

We should not use a star-delta starter if the required (application or load) torque is more than 50% of the three-phase induction motor’s rated torque.