STAR-DELTA Starter Motor Starting Method Without Timer

Electrical Technology

Starting & Controlling of 3-Phase Motor using Semi-Automatic Star-Delta Starter Without Timer

Electric motors are essential components in various industrial applications and play a vital role in powering machines, pumps, compressors, and other equipment. However, when it comes to starting large motors, the initial inrush current can be significantly high, leading to voltage drops and potential damage to the motor windings. That’s why do we need a PLC, VFD, or a motor starter such as a Star-Delta Starter.

To overcome this challenge, engineers have developed various motor starting methods, and one such method is the “Star-Delta Starter.” As we have explained the automatic star-delta starter using timer in the previous post, In this article, we will explore the power and control diagram, working principle and applications of semiautomatic or manual star-delta starter without using a timer.

Introduction to Star-Delta Starter

A star-delta starter is a widely used method for starting three-phase induction motors. It allows for a gradual reduction of the starting current, reducing the impact on the power supply and the motor itself. Typically, an automatic star-delta starter uses a time delay relay to switch between the star and delta connections of the motor windings. However, in some cases, the use of a timer may not be necessary or practical, especially in applications where simplicity and cost-effectiveness are crucial.

Working Principle of Star-Delta Starter without Timer

The star-delta starter without timer follows a basic principle: the motor starts in a star configuration, and after a predefined time, it switches to the delta configuration. This methods uses when a time delay timer is faulty or not available during the emergency operation of large motors.

Unlike the conventional star-delta starter, this method does not use a time delay relay. Instead, it relies on manual control for the switching process e.g. using push button switches for manual operation for transferring the mains connection from Star to Delta.

Star Connection

During the starting process, the motor windings are initially connected in a star (Y) configuration. In the star connection, each winding receives the full line voltage (V_L) across them. This configuration allows the motor to draw reduced current compared to a direct-on-line start.

Delta Connection

After a specific period (usually a few seconds) of running in star mode, the motor windings are switched to a delta (Δ) configuration. In the delta connection, each winding receives the line voltage divided by the square root of 3 (√3) across them. This results in an increase in the current but provides higher torque, allowing the motor to reach its full speed.

Power Diagram:

Schematic Wiring Diagram:

Control Circuit Diagram:

Control Wiring Diagram:

Manual Control Procedure

The manual control procedure for the star-delta starter without timer is relatively simple. It involves the following steps:

Initial State: The motor is at rest, and the windings are disconnected.
Star Connection: Press the “Start” button or close the start contactor. This connects the motor windings in a star configuration.
Star Mode Operation: The motor runs in the star configuration for a predetermined time to reduce the starting current.
Delta Connection: After the time delay (manually measured or estimated), press the “Changeover or pushbutton” button or close the changeover contactor. This switches the motor windings from star to delta configuration.
Delta Mode Operation: The motor runs in the delta configuration, reaching its full speed and providing the necessary torque for the intended load.
Stopping the Motor: To stop the motor, press the “Stop” button or open the main contactor.

Advantages

The Star-Delta Starter without Timer offers several advantages:

The absence of a time delay relay simplifies the control circuit. It reduces the chances of timer-related failures and eliminates the need for adjusting the timer based on motor size and specifications.
The removal of the timer component reduces the overall cost of the starter. This makes it an attractive option, especially for small to medium-sized motor applications, where cost plays a significant role in equipment selection.
With fewer components involved, the star-delta starter without timer improves the overall reliability of the motor starting process. The manual control procedure is straightforward and less prone to electronic or electrical malfunctions.
The simplified design reduces maintenance efforts and costs. Technicians can easily troubleshoot and replace faulty components if necessary, without dealing with intricate timer circuits.

Applications

The Star-Delta Starter without Timer finds application in various industries, including:

Agriculture: Irrigation pumps and agricultural machinery.
Manufacturing: Fans, blowers, conveyors, and compressors.
Mining: Crushers and large conveyor systems.
Oil and Gas: Pumps and compressors for fluid transportation.
Water Treatment: Water pumps and purification systems.

Abbreviations:

R ,Y, B = Red, Yellow, Blue or Brown, Black, Gray ( 3 Phase Lines L1, L2, L3)
C.B & MCCB = General Circuit Breaker & Molded Case breakers
Mains = Main Supply
Y = Star
Δ = Delta
O/L = Over Load Relay
NO = Normally Open
NC = Normally Closed K1 = Contactor (Contactor coil) K1/NO = Contactor Holding Coil (Normally Open)
K1 , K2, K3 = Contactors