Transformers

Question 1

What are two types of core losses associated with a transformer?

Answer 1

Hysteresis

Eddy currents

Question 2

Describe induction

Answer 2

The process of by which a voltage is produced by the interaction of a conductor and a magnetic field

Question 3

What is inductance

Answer 3

The property of a circuit that opposes change in current

Question 4

What is mutual induction

Answer 4

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

Question 5

True or false

The primary coil is always connected to the source

Answer 5

True

Question 6

True or false

The primary side of a transformer is the high side (H1,H2)

Answer 6

False

The primary side is the supply side. It can be high or low

Question 7

What are the three basic types of transformers (construction)

Answer 7

Core type
H type
She’ll type

Question 8

True or false

The core type xmer has the most leakage flux

Answer 8

True

Question 9

True or false the shell type transformer construction has the least leakage flux

Answer 9

True

Question 10

True or false

Transformers are rated in true power

Answer 10

False
They are rated in apparent power.
kVa input = kVa output

Question 11

Why is a short circuit test performed on a transformer immediately after it is manufactured?

Answer 11

To determine the %IZ

Question 12

What is impedance voltage

Answer 12

The primary voltage required to circulate the rated full load secondary current when the secondary winding is short circuited at the terminals.

Question 13

True or false

The secondary coil of a transformer is not always connected to the load

Answer 13

False

The secondary IS ALWAYS connected to the load.

Question 14

If the turns of the secondary coil are decreased what will happen to the induced voltage

Answer 14

It will decrease

Question 15

What are three types of transformer losses

Answer 15

Eddy currents
Hysteresis
I2R Losses

Question 16

What type of test is performed to find out the core losses of an xmer

Answer 16

An open circuit test

Question 17

Why are xmer ratios so important ?

Answer 17

They can be used to determine voltage, current and apparent power in the primary and secondary turns.

Question 18

What is the purpose of transformer taps in the primary side door

Answer 18

To obtain proper secondary voltage.

Question 19

Why are taps used on the secondary of a transformer

Answer 19

To supply more than one voltage

Question 20

What is another name for mutual induction

Answer 20

Transformer action

Question 21

The small current that flows in the primary winding of a transformer while connected to and ac supply is known as what?

Answer 21

Exciting current

Question 22

The overall magnetic flux from no load to full load will:
A   stay nearly the same
B   Vary proportional to load
C   Vary inversely proportional to load
D.   Is always zero

Answer 22

Stay nearly the same. Within in a few %

Question 23

What type of test is used to determine core losses

Answer 23

Open circuit test

Question 24

What are the three main parts of a transformer

Answer 24

Core
Primary windings
Secondary windings

Question 25

What does the va or the kVa rating of a transformer represent

Answer 25

Full load output

Question 26

What is the formula to calculate the power factor

Answer 26

Pf = P/S True power over apparent power W/VA

Question 27

A transformer can operate up to what percent of its its rated voltage

Answer 27

110%

Question 28

What is the formula for calculating the number of turns in a xmer winding

Answer 28

Number of turns = primary turns / volts per turns

Question 29

What is the formula to find voltage regulation

Answer 29

Vreg = v no load - full load / V full load

Question 30

What is the main component that limits exciting current

Answer 30

Primary induced voltage aka counter emf (XL)

Question 31

True or false | Under load conditions the secondary current flux opposes primary current flux

Answer 31

True

Question 32

When load is added toe an xmer, what will happen to the overall magnetic flux?

Answer 32

It will increase

Question 33

What is the formula for efficiency of an xmer

Answer 33

``` %eff = Pin / Pout Pin = Pout + losses ```

Question 34

When paralleling transformers what must be identical on the transformers

Answer 34

Secondary volages Same %IZ within 5% Same tap settings

Question 35

The current in the series winding of an auto transformer is also known as

Answer 35

The primary line current

Question 36

The series coil current in a step down auto transformer is the same as the primary line current True or false

Answer 36

True

Question 37

Compared to a mutual induction transformer, the auto transformer will have a higher short circuit current Tue or false

Answer 37

True

Question 38

What is the transformed apparent power rating of for an auto transformer a product of

Answer 38

The product of of the rated common winding voltage times the rated common winding current of an autotransformer

Question 39

Describe conducted power of an autotransformer

Answer 39

The product of the rated common winding g voltage times the rated series winding current of an autotransformer