# What is autotransformer starting method?

## What is autotransformer starting method?

In the autotransformer starting method, the starter is connected to a particular tapping of the autotransformer to obtain the most suitable starting voltage. A changeover switch S is used to connect the autotransformer in the circuit for starting the motor.

How many contactors are needed for auto transformer starter?

An autotransformer is used to reduce the voltage at the starting time of the motor. It has a total of 9 terminals. Among those three terminals are the main input terminals that are connected to the incoming power supply through the transformer contactor.

### How the voltage is reduced in auto transformer starter at the time of starting?

The autotransformer reduced-voltage starter places the motor on the secondary of the autotransformer while starting. The taps on the autotransformer limit the voltage applied to the motor to 50%, 65% or 80% of the nominal voltage.

How do you calculate autotransformer?

Steps for Solving Auto-Transformer Calculations

1. Assign polarities – load polarity is determined by which terminal is most positive with respect to the other terminal.
2. Calculate max high and low voltage winding ampacity.
3. Plot current flow through the load and the series load winding.

## What is the difference between star delta starter and auto transformer starter?

Aside from the amount that the starting voltage (And current) is decreased, Star delta starters require three sets of contactors while autotransformer starters require four sets of contactors and a three phase autotransformer (or two single phase transformers to be connected as an autotransformer).

What is the major disadvantage of the autotransformer starter?

The main disadvantage of an autotransformer is that it does not have the primary to secondary winding isolation of a conventional double wound transformer. Then an autotransformer can not safely be used for stepping down higher voltages to much lower voltages suitable for smaller loads.

### How does an autotransformer work?

Operation. An autotransformer has a single winding with two end terminals and one or more terminals at intermediate tap points. It is a transformer in which the primary and secondary coils have part of their turns in common. The portion of the winding shared by both the primary and secondary is the common section.

What is a 3 phase auto transformer?

3-Phase Autotransformer Three phase auto transformer is used for such application where small voltage is used in distribution system. There is no electrical isolation is provided between them. It is designed for step up and step down voltage and work on magnetic induction principle.

## What is difference between DOL and star-delta?

The most common starting method I have ever seen is DOL. However Star Delta and VSD starters are also used for larger motors. In this article I will discuss DOL starter vs Star Delta starter….

DOL Starter Star Delta Starter
Full voltage is applied to the motor at the starting The voltage is reduced to a lower value

What is an autotransformer starter?

An Autotransformer Starter is suitable for both star and delta connected motors. In this method, the starting current is limited by using a three-phase autotransformer to reduce the initial stator applied voltage. The figure below shows the motor with the autotransformer starter: It is provided with a number of tappings.

### What is the limit of starting voltage of auto transformer?

The taps provided on auto-transformer limit the starting voltage and supply motor in steps of 50% 65% or 80% of nominal voltage. Using auto transformer for starting purpose the line current is always less than motor nominal current during start, because of motor connected to the secondary side of auto-transformer starter during acceleration.

How does an auto-transformer motor work?

On starting, the motor is connected to the tappings of the auto-transformer; transformer contactor K2M and star contactor K1M are closed. The motor starts at the voltage reduced by the transformer, with a correspondingly smaller current.

## What is the purpose of using auto transformer for starting purpose?

Using auto transformer for starting purpose the line current is always less than motor nominal current during start, because of motor connected to the secondary side of auto-transformer starter during acceleration. If motor connected to 50% tap of auto transformer, the motor current would be reduced up to 50% of nominal starting current.