# Basic Electrical Engineering Autotransformers Quiz

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## 12 Questions

### What decides the cross-sectional area of a wire?

The value of current flowing through it

### How is the length of a wire related to the number of turns?

The length is proportional to the number of turns

Area and length

### In a two-winding transformer, how is the total weight of copper calculated?

Total weight of copper = Weight of first winding + Weight of second winding

### What is the advantage of using an autotransformer compared to a conventional transformer?

Reduced copper usage and size

### What is a disadvantage of an autotransformer?

No electrical isolation between primary and secondary windings

### Explain the configuration of an autotransformer when the number of turns N is less than N₁.

Step down transformer configuration.

### Describe how an autotransformer functions as a step up transformer.

When the number of turns of winding AB (N₂) is higher than the number of turns of winding CB (N₁), the autotransformer acts as a step up transformer.

Winding CB.

### Where is the load connected in an autotransformer when operating as a step up transformer?

Between terminals A and B.

### Explain how an autotransformer achieves copper saving compared to a two-winding transformer.

By using a part of the winding as a common winding for both primary and secondary.

### What is the purpose of autotransformer in electrical engineering?

To efficiently step up or step down voltages.

## Study Notes

### Autotransformer Configurations

• An autotransformer operates as a step-down transformer when the number of turns N is less than N₁.
• When the autotransformer is configured as a step-up transformer, the part CB of the complete winding acts as the primary winding, and the full winding AB acts as a secondary winding.

### Autotransformer as a Step-Up Transformer

• The input voltage V₁ is applied between terminals C and B.
• The load is connected between terminals A and B.
• The number of turns of winding AB (N₂) is higher than the number of turns of winding CB (N₁), resulting in a step-up transformer.
• The load voltage V₂ is equal to N₂/N₁ times V₁.

### Copper Saving in Autotransformer

• The cross-sectional area of a wire is decided by the value of current flowing through it.
• The length of the wire is proportional to the number of turns.
• The weight of copper required is proportional to area and length.
• The weight of copper is proportional to NI (number of turns times current).
• In a two-winding transformer, the total weight of copper is W = W₁ + W₂.
• In a step-down autotransformer, the total weight of copper is W = [(N₁-N₂)/N₁] × W₁.
• Copper saving takes place if an autotransformer is used instead of a two-winding transformer.

• The size of the autotransformer is smaller than that of a conventional transformer.
• The cost of the autotransformer is lower due to reduced copper requirements.
• The efficiency of the autotransformer is higher than that of a conventional transformer due to reduced resistance.
• The autotransformer has fewer losses than a conventional transformer.

• There is no electrical isolation between the primary and secondary windings.
• The autotransformer is not suitable for high voltage applications.

Test your knowledge on autotransformers in Basic Electrical Engineering. Questions cover topics such as step-down transformer configuration, step-up transformer configuration, and diagrams explanation.

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