2-7) Transformer Operation

Question 1

What does a transformer do and how does it work?

Answer 1

It transforms electrical energy into magnetic energy then back into electrical energy again. Transformers are necessarily AC because their operation depends on electromagnetic induction between two stationary coils and magnetic flux of changing magnitude and polarity.

Question 2

What is the role of the “primary” and “secondary” in a transformer?

Answer 2

Source voltage is directed onto a coil called the “primary.” The “secondary” coil is where the output, or induced voltage, is generated. The fundamental significance of a transformer is its ability to step voltage up or down from between the primary and the secondary. Power is not gains or lost between the primary and secondary.

Question 3

What is the relationship between voltage and current in the primary and voltage and current in the secondary of a transformer?

Answer 3

Voltage and current have an inverse relationship in the windings of a transformer. A primary coil with more turns than the secondary will have higher voltage than the secondary but lower current than the secondary. So a transformer steps down voltage with fewer turns in the secondary than in the primary, voltage will decrease in the secondary but current will increase. Total power (current x voltage) will remain the same between the primary and secondary.

Question 4

In a transformer, what is the relationship between voltage in the secondary to voltage in the primary compared to the number of turns in the primary and the number of turns in the secondary?

Answer 4

The ratio of voltage in the secondary and primary is the same as the ratio of turns in the secondary and primary. More turns in the secondary than primary will step up the voltage. Fewer turns in the secondary than primary will step down the voltage.

Question 5

What is a formula to describe the relationship of voltage and coil turns in a transformer?

Answer 5

V_S / V_P = N_S / N_P

Secondary Voltage : Primary Voltage = Secondary Turns : Primary Turns

A transformer is a voltage conversion device where the ratio of the number of turns is directly proportional to the change in voltage. Once the voltage is changed, then the rest of the circuit is just like any other Ohm’s Law calculation.

Question 6

How is a step up transformer structured?

Answer 6

If there are more coil turns in the secondary winding than in the primary winding, the secondary output voltage will be higher than the primary input voltage.

Question 7

How is a step down transformer structured?

Answer 7

If there are fewer coil turns in the secondary than in the primary, then the secondary output voltage will be lower than the primary input voltage.

Question 8

What are the steps to determine the turns ratio for this transformer?

Answer 8

1. Solve for voltage in the secondary using Ohm’s Law: E_S = 1500 ohms x 3.5A = 5,625V
2. Use transformer voltage : turns ratio formula: V_P / V_S = N_P / N_S = V_P/V_S = 1,125V / 5,625 = 1/5
3. Answer: 1/5