Autotransformers

Question 1

What is the difference between a mutual induction transformer and a self induction transformer?

Answer 1

Self induction transformers have a physical connection point between the two windings

Question 2

An autotransformer is a self induction transformer.

True / False

Answer 2

True

Question 3

Name the two windings found in an autotransformer.

Answer 3

Common winding

Series winding

Question 4

In an autotransformer some of the apparent power is (transformed/conducted), and the rest of it is (transformed / conducted)

Answer 4

In an autotransformer some of the apparent power is TRANSFORMED, and the rest of it is CONDUCTED.

Question 5

How is transformed power calculated?

Answer 5

Transformed VA =

Icomm • Vcomm

(Common winding)

Question 6

How is conducted VA calculated?

Answer 6

Conducted power =

Iser • Vcomm

(Iser = series winding current)

Question 7

How do we calculate the total VA rating of an auto transformer?

Answer 7

Total VA =

Transformed VA + Conducted VA

Question 8

There are lots of calculations in this section

I promise to work through the examples in the module ! 🤓

Answer 8

I

P-R-O-M-I-S-E!!!

📚 📖 🎓

Question 9

List the advantages of autotransformers.

Answer 9

• ideal for small voltage changes
• smaller in size and lower in cost than mutual induction Tx’s
• better %Vreg

(Vreg = voltage regulation)

Question 10

List the disadvantages of autotransformers

Answer 10

• secondary cct NOT isolated from primary cct
• higher available short cct currents (because lower Vreg)
• common winding is open in a step-down auto Tx, so source applied directly to load. Could damage load and create serious shock hazard