What is Star-Delta Starting method?

There are several types of motor starts, including:-

1. Direct-On-Line (DOL) Start

2. Star-Delta Start

3. Auto-Transformer Start

4. Soft Starter

5. Variable Frequency Drive (VFD) Start

Now, let’s briefly explain the Star-Delta Start:What is Star-Delta Start?

A Star-Delta starter is a type of reduced voltage starter used for starting three-phase induction motors. It’s a method of starting a motor with a reduced voltage, followed by a switch to full voltage once the motor reaches a certain speed.

Connections:-

1. Star Connection (initial start):

i)Motor windings connected in a star (wye) configuration.

ii)Voltage across each phase reduced by 1/√3.

iii)Initial power supply from MCCB (Molded Case Circuit Breaker) and also it provide short circuit protection.

2. Delta Connection (after switching):-

i)Motor windings connected in a delta configuration

ii)Full voltage applied across each phase

iii)Power supply from MCCB, then transferred to Contactor and finally to the motor

Contactor Configuration:-

There are three contactors used in a Star-Delta starter:

1. Main Contactor (M): Connects the motor to the power supply

2. Star Contactor (S): Connects the motor windings in a star configuration during starting

3. Delta Contactor (D): Connects the motor windings in a delta configuration after switching

Working principal:-

1. The motor starts in a star configuration, with reduced voltage and current, supplied from the MCCB.

2. The starter timer (usually set between 10-30 seconds) allows the motor to reach 70-80% of full speed.

3. At the end of the set time, the starter switches to a delta configuration: – Star Contactor (S) opens – Delta Contactor (D) closes – Power supply transferred from MCCB to Contactor and finally to the motor

4. In the delta configuration, full voltage is applied across each phase, increasing torque and allowing the motor to reach full speed.

Shifting Time:The shifting time from star to delta connection is typically set between 5-30 seconds, depending on the motor’s characteristics and the application’s requirements

.NOTE : This method is suitable and applied for motor having power ratings 20kW or upto it.

Advantages:

1. Reduced starting current (1/3 of DOL starting current)

2. Reduced starting torque

3. Smoother acceleration

4. Reduced voltage drop during starting

Disadvantages:-

1. More complex and expensive than DOL starters

2. Requires additional switching equipment

3. May cause voltage fluctuations during switching

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