What is autotransformer motor starter?

What is autotransformer motor starter?

The autotransformer starter is a special type of motor starter that enables the start of squirrel-cage motors using a reduced starting current since the voltage is reduced during the start. With an autotransformer start, a device called a transformer is used.

Is another name for an autotransformer starter?

The term variac has become a genericised trademark, being used to refer to a variable autotransformer.

What are the advantages of autotransformer starter?

Advantages of Auto Transformer starters

• Its efficiency is more when compared with the conventional one.
• Its size is relatively very smaller.
• Voltage Regulation of autotransformer is much better.
• Lower cost.
• Low requirements of excitation current.
• Less copper is used in its design and construction.

What is the working principle of an autotransformer starter?

Autotransformer is a single winding transformer that works on the principle of Faraday’s Law of electromagnetic induction. Mostly used in low voltage range, for industrial, commercial and laboratory purposes. Also known as variac, dimmer stat, etc. autotransformer can be single and three-phase.

What is the disadvantage of autotransformer?

Disadvantages of an Autotransformer Larger short-circuit current. No isolation exists between the primary and secondary windings. Only useful for moderately smaller voltage changes.

Why is autotransformer used?

The primary purpose of an autotransformer is to regulate the voltage of transmission lines and can be used to transform voltages. With only one winding, an autotransformer adjusts the voltage automatically according to load.

What is the purpose of autotransformer?

Autotransformers serve the purpose buck and boost transformer as it functions to increase or decrease the supply voltage by a minimum amount. These are the excellent replacements for full transformers in case the voltage ratio is fairly small lower than four in between the primary and secondary.

What is the working principle of autotransformer?

How does an autotransformer motor starter work?

Autotransformer starting involves inserting an autotransformer in between the motor and the source. The voltage that is fed to the autotransformer input is reduced in proportion to the ‘tap’ setting of autotransformer at the output. Typical settings for tap settings for autotransformer motor starters are 50%, 65%, 80%.

Is a star delta starter equivalent to an autotransformer starter?

Here equation (5) and equation (8) show that with an autotransformer, the starting current I’ stl from the main supply and the starting torque is reduced to the x 2 times to the corresponding values with the direct online starting. Thus, the star delta starter is equivalent to an autotransformer starter of the ratio x = 0.58.

How do you start an auto transformer?

Auto transformer Starter. A double throw switch S is used to connect the auto transformer in the circuit for starting. When the handle H of the switch S in the START position. The primary of the auto transformer is connected to the supply line, and the motor is connected to the secondary of the auto transformer.

What is the motor current at the starting point of auto transformer?

With auto transformer starting, if tapping of the transformer ratio x is used, then the voltage per phase across the motor is xV 1. Therefore, at the starting, the motor current is given by the equation: