Introduction to transformers

Question 1

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

Answer 1

Induction

Question 2

The property of a circuit that opposes change in current

Answer 2

Inductance

Question 3

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

Answer 3

mutual induction

Question 4

a Transformer transfers energy from one AC circuit to another through…

Answer 4

Electromagnetic Induction

Question 5

The secondary AC Frequency will be the ________ as the Primary AC frequency

Answer 5

same

Question 6

The magnetic circuit of a transformer is usually a path of

Answer 6

low reluctance

Question 7

Two Common Core losses are?

Answer 7

Eddy currents and hysteresis

Question 8

Transformer cores are constructed with this material to prevent hysteresis?

Answer 8

Silicon steel

Question 9

What is done to reduce transformer eddy currents

Answer 9

The core is constructed with thin laminted steel and coated with varnish to insulated them from on another

Question 10

Three basic types of transformer construction are?

Answer 10

Core typed, Shell type and H type

Question 11

Which type of transformer has the least leakage flux?

Answer 11

The H-type.

Question 12

Transformers usually have an efficiency of ?

Answer 12

95 % to 98%

Question 13

The unwanted current flow induced in a core producing heat (power losses) is called?

Answer 13

Eddy currents

Question 14

Magnetic flux lines that are established outside the core and windings that constitute a small amount of lost energy

Answer 14

leakage flux

Question 15

Basic transformer name plates indicate

Answer 15

primary voltage, secondary voltage, VA or KVA rating

Question 16

The capacity of a transformer is rated in

Answer 16

KVA or VA

Question 17

Other information that may be on a transformer nameplate

Answer 17

frequency, temperature rise, percent impedance, type of insulating oil, serial number, type number and single or three phase.

Question 18

The transformer winding that is connected to the input voltage or energy source

Answer 18

Primary winding

Question 19

The transformer winding that is connected to the load

Answer 19

Secondary winding

Question 20

A transformer name plate does not list this rating.

Answer 20

Current, (Current is calculated using the KVA and Voltage)

Question 21

The percent impedance of a transformer is used to calculate?

Answer 21

transformer losses, voltage regulation and system short circuit currents

Question 22

The impedance of a transformer is affected by

Answer 22

The amount and type of core, winding wire size, number of winding turns and degree of magnetic coupling

Question 23

This test is done to determine a transformers percent impedance after manufacturing.

Answer 23

A short circuit test

Question 24

Transformers are used for these 3 applications

Answer 24

1. step up voltage of a circuit 2.step down the voltage of a circuit 3. isolate on circuit from amother

Question 25

The type of transformer generally used in a power station switch yard before transmission

Answer 25

Step up

Question 26

The type of transformer generally used before consumer use.

Answer 26

Step down

Question 27

what does an isolation transformer do

Answer 27

Isolates the secondary from ground, isolates the output from the supply voltage through transformer action and has a 1:1 transformer ratio (no voltage change from primary to secondary)

Question 28

ANSI stands for:

Answer 28

American National Standards Institute

Question 29

ANSI requires high voltage windings of a transformer to be identified with…

Answer 29

A capital letter H

Question 30

ANSI requires the low voltage winding of a transformer to be identified with..

Answer 30

A capital letter X

Question 31

A transformers VA input equals

Answer 31

VA output

Question 32

A transformer typically withstand ________ of its rated voltage.

Answer 32

110%

Question 33

The turns ratio

Answer 33

Np/Ns or Np:Ns

Question 34

The voltage ratio

Answer 34

Vp/Vs or Vp:Vs

Question 35

The current ratio

Answer 35

Ip/Is or Ip:Is

Question 36

The apparent power ratio is always

Answer 36

1:1 (VA in = VA out)

Question 37

The Volts per-turn ratio

Answer 37

Vp / Np or Vs/Ns

Question 38

Polarity of a transformer is important

Answer 38

when paralleling transformers or making a three phase bank from single phase transformers

Question 39

When looking at a transformer from the low voltage side. H1 is always marked on

Answer 39

the upper left side

Question 40

when looking at an additive transformer from the low voltage side X1 would be marked on

Answer 40

Bottom right side

Question 41

when looking at a subtractive transformer from the low voltage side X1 would be marked on the

Answer 41

Bottom left side

Question 42

ANSI requires that every winding lead marked with an even number shall have the same ______

Answer 42

Instantaneous polarity

Question 43

Primary transformer taps are used when

Answer 43

The supplied voltage does not exactly match the rated nameplate voltage

Question 44

tapped secondary winding are used when

Answer 44

more than one output voltage may be required

Question 45

% tap formula

Answer 45

% tap = (Actual Vp - Rated Vp)/rated Vp x 100

Question 46

FCBN

Answer 46

Full Capacity Below Normal

Question 47

FCAN

Answer 47

Full Capacity Above Normal

Question 48

RCBN

Answer 48

Reduced Capacity Below Normal

Question 49

If a RCBN tap was used

Answer 49

The KVA Capacity would also be reduced

Question 50

Taps can be changed by

Answer 50

moving the lead termination, moving connecting bars or using a rotary switch if installed.

Question 51

when changing the taps transformer must be

Answer 51

De-energized unless otherwise stated

Question 52

This device will automatically adjust the secondary voltage to a preset value

Answer 52

Automatic tap changer