Introduction To Transformers

Question 1

Describe induction

Answer 1

The process of producing a voltage by the interaction of magnetic fields and a conductor

Question 2

Describe mutual induction

Answer 2

When a change of current in one circuit causes a voltage to be induced into another circuit

Also called transformer action

Question 3

What are the 2 types of transformer losses

Answer 3

Eddy currents
Hysteresis

Question 4

Describe hysteresis

Answer 4

1. Losses due to molecular friction caused by reversal of the direction of current flow
2. Proportional to frequency of source voltage, higher the frequency, greater the loss
3. Can be limited by using silicon steel in construction

Question 5

Describe eddy currents

Answer 5

1. Currents that are induced into the metal core material by the changing magnetic field
2. Can be limited by using laminated sheets

Question 6

What are the 3 types of transformers

Answer 6

1. Core
2. Shell
3. H-type

Question 7

Which transformer type has the least leakage flux and which has the most

Answer 7

Core type has the most
H-type has the least

Question 8

What is the primary winding

Answer 8

The winding that is connected to the input voltage

Question 9

What is the secondary winding

Answer 9

The winding that is connected to the load

Question 10

Describe percent impedance

Answer 10

1. Used for calculating transformer losses, voltage regulation, and system short circuit currents
2. It is found by performing a short circuit test

Question 11

What are three functions of single phase transformers

Answer 11

1. Step up the voltage
2. Step down the voltage
3. Isolate one circuit from the other

Question 12

What is the purpose of using taps on transformers

Answer 12

To obtain the proper name plate voltage

Question 13

What is the meaning of a tap labeled 5% FCBN

Answer 13

1. This tap would be used when the primary supply voltage is 5% lower than the rated transformer primary voltage
2. Because it’s a full capacity tap, KVA will be maintained

Question 14

What is the meaning of a tap labelled 5% FCAN

Answer 14

1. The tap would be used when the primary supply voltage is 5% higher than the rated transformer primary voltage
2. Rated KVA capacity is maintained

Question 15

What is the meaning of a tap labelled 2.5% RCBN

Answer 15

1. The tap would be used when the primary supply voltage is 2.5% lower than rated transformer primary voltage
2. Because it is a reduced capacity transformer, the rated KVA will also be reduced