Worksheet 20-Transformer Operation

Question 1

What are the two parts of a transformer?

Answer 1

The two parts of a transformer are the primary and the secondary windings.

Question 2

What is the normal purpose of a transformer?

Answer 2

A transformer is designed to transform one voltage value to another.

Question 3

In a transformer, when you change voltage, what other value changes proportionally?

Answer 3

When the value of voltage is stepped up in a transformer, the current in the circuit must decrease. When voltage is stepped down, current must increase.

Power remains unchanged–it’s not gained or lost because P = V x I

Question 4

Describe what is happening to voltage and current when you have a step down transformer.

Answer 4

When a voltage is stepped down in a transformer, current will increase.

Question 5

Given the following information: Primary Voltage 120V, Secondary Voltage 60V, what is the transformer ratio and is this a step up or step down transformer?

Answer 5

When the primary voltage is 120 and the secondary voltage is 60, the turns ratio will be 2:1, which is a step-down transformer (120/60 = 2/1)

Question 6

What is the input voltage of a 10:1 transformer when the output is 60VAC?

Answer 6

The input of the primary is 10 times the secondary; this puts the output as a multiple of the input.

10 x 60 = 600 volts. The input is 600 volts.

Question 7

What is the current of the secondary of a 10:25 transformer when the primary current is 50A?

Answer 7

The ratio of this transformer is 1 to 2.5, which is a step up transformer. Current changes inversely to voltage in a transformer.

50A / 2.5 = 20A

Check: to check the work, plug in values for voltage to make sure power is unchanged:

Vp=10V
Vs=25V
Pp = 10V x 50A = 500W
Ps = 25V x 20A = 500W

Question 8

What is the turns ratio of a transformer when the primary voltage is 30 volts and the secondary voltage is 900 volts?

Answer 8

If the primary is 30 and the secondary is 900, then the ratio is divided 30/900 = 1 / 30

Question 9

What is the output voltage of a transformer with 300 turns in the primary and 900 turns in the secondary with an input voltage of 45 VAC?

Answer 9

The voltage of the primary is 45 then the secondary voltage is 135 is a 3:1 transformer:

45 / X = 300 / 900
45 / X = 1 / 3
X = 135V