Single Phase Transformers

Question 1

What is used to indicate a direction of additive or subtractive polarity on a schematic

Answer 1

Arrows

Question 2

Transformer cores are assembled from many thin sheets of metal. This type of construction is called __________?

Answer 2

Laminated

Question 3

A Tape-wound core is also called ____________?

Answer 3

Toroid

Question 4

When testing a transformer, what will reveal problems of insulation breakdown a ohmmeter will not ?

Answer 4

Megger

Question 5

A transformer in which the SECONDARY voltage is higher then the primary, is called what ?

Answer 5

Step up transformer

Question 6

What is expressed by (%Z)

Answer 6

Transformer Impedance

Question 7

Any transformer flux that does not follow the core and escapes into surrounding air is called ?

Answer 7

Flux leakage

Question 8

Moving coils farther apart increases the amount of _____________?

Answer 8

Magnetic flux leakage

Question 9

What induces a voltage in the secondary for a transformer ?

Answer 9

Primary current

Question 10

The current of the secondary induces a __________ in secondary windings that is in opposition to the counter voltage induced in the primary

Answer 10

Countervoltage

Question 11

In a transformer, even with no load connected, there will be small current flow known as _________ current

Answer 11

Exciting

Question 12

Is = kVA/Es is a calculation of what?

Answer 12

Max current in secondary

Question 13

A transformer has a 2:1 turns ratio. 120V is applied to the primary. What is the secondary voltage ?

Answer 13

60V

Question 14

What type of core is found in high voltage distribution transformers

Answer 14

H-type

Question 15

A transformer that has ONE winding, that is both used for primary and secondary is what ?

Answer 15

Auto transformer

Question 16

A transformer in which the primary and secondary are physically separated and not connected by a conductor is called ?

Answer 16

Isolation transformer

Question 17

Transformer that converts high voltage from hydro down to 240/120V for homes is called ?

Answer 17

Distribution transformer

Question 18

A magnetically operated machine that can change values of voltage, current and impedance without changing frequency ?

Answer 18

Transformer

Question 19

When a transformer is shown on a schematic diagram, what is the common practice to indicate polarity of windings ?

Answer 19

Using Dots ?

Question 20

What should the ohmmeter indicate when testing for shorted windings between primary and secondary

Answer 20

Infinity

Question 21

The industrial use of transformers that normally had 240-480V primary and a 120V secondary is called a __________ transformer.

Answer 21

Control

Question 22

In a 60hz AC cct, how many times does the voltage change polarity ?

Answer 22

120

Question 23

The Output winding is called ???

Answer 23

Secondary

Question 24

A tape-wound core is assembled by ?

Answer 24

Winding a long continuous tape in a spiral

Question 25

In a transformer, the turns of primary wire compared to the turns of secondary wire is called the ________ratio.

Answer 25

Turns

Question 26

Connected the secondary windings of a transformer in ____________ to increase the current capacity

Answer 26

Parallel

Question 27

A transformer in which the secondary voltage is less then the primary is called ?

Answer 27

Step down

Question 28

The amount of current that flows into a transformer primary when voltage is first applied is called ________ current

Answer 28

Inrush

Question 29

Power INPUT winding of a transformer is called ?

Answer 29

Primary

Question 30

What should be disconnected first it is necessary to remove the transformer for service ?

Answer 30

Secondary

Question 31

Are core losses fixed or variable ?

Answer 31

Fixed

Question 32

Are copper losses fixed or variable ?

Answer 32

Variable

Question 33

How can losses be reduced for eddy currents ?

Answer 33

Laminations

Question 34

How can losses be reduced for hysteresis?

Answer 34

Silicon steel

Question 35

What test is performed with a OPEN primary

Answer 35

Open circuit, core test

Question 36

What test is being performed with a closed/ shorted primary

Answer 36

Short circuit test ( Cooper losses)

Question 37

What percent is excitation current ?

Answer 37

2-5%

Question 38

A CT is a example of a _________ transformer

Answer 38

Toroidal

Question 39

The transformer with the highest efficiency is ?

Answer 39

H type oil filled … 99% EFF

Question 40

2 forms of transformer cooling are ?

Answer 40

Natural convection
Forced (pumps, fans, air, water, oil)

Question 41

What transformer has high losses and is used for LOW power applications?

Answer 41

Core type (1 window) 90-95% EFF

Question 42

What transformer is used for medium power applications?

Answer 42

SHELL TYPE 2 window (93-95%)

Question 43

What are pros and cons of a Cross type transformer

Answer 43

Pros : almost no leakage 95-98% EFF

Cons: heavy, higher costs, high power costs