Theory

Question 1

In a transformer, with no load connected. There is some small current required to magnetize the core. This is called

Answer 1

Excitation current

Question 2

Ideally the material used in a transformer should have a property of ______________ retentivity

Answer 2

Low

Question 3

Ideally the material used in the core of a transformer should have property of ___________ permeability

Answer 3

High

Question 4

Ideally the material used in the core of a transformer should have property of ____________ resistance

Answer 4

High

Question 5

Transformer in which the secondary is more than the primary voltage is called a

Answer 5

Step up transformer

Question 6

Transformer that converts a high 7200V from the utility down to 120/240 is called a

Answer 6

Distribution transformer

Question 7

The magnetically operated device that can change values of voltage current and impedance without changing frequency is a

Answer 7

Transformer

Question 8

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

Answer 8

Flux leakage

Question 9

A transformer in which the secondary voltage is less than the primary voltage is a

Answer 9

Step down transformer

Question 10

An industrial transformer that normally has small VA 240v or 480v primary and a 120v secondary is called

Answer 10

A control transformer

Question 11

A transformer that doesn’t isolate the input from the output is called

Answer 11

A auto transformer

Question 12

Two to design characteristics that are used in the construction to reduce core losses

Answer 12

Layered core
Soft steel

Question 13

The efficiency of practical transformers is a range of

Answer 13

96-99%

Question 14

Difference between transforming AC and DC

Answer 14

DC cannot be transformed

Question 15

The primary of a transformer is a ________ and the secondary is a ___________

Answer 15

Load

Source

Question 16

What can transformers do

Answer 16

Change voltage
Change currents
Change impedance

Question 17

What is mutual induction

Answer 17

When changing current in one coil induces an EMF in the other

Question 18

Primary is side with _______ energy

Answer 18

Input

Question 19

Secondary is the side with ________ energy

Answer 19

Output

Question 20

Currents that circulate in the core are called

Answer 20

Eddy currents

Question 21

What can you do to increase output and decrease losses

Answer 21

Layered laminated core

Question 22

What is retentivity

Answer 22

The ability to retain a magnetic field after source has been lost

Question 23

Benefit of a polyphase transformer

Answer 23

Easier to wire

Question 24

Con of a polyphase transformer

Answer 24

If you lose a winding will have to get a new transformer or rebuild old one.

Question 25

Benefit of 3 single phase transformers in bank connection

Answer 25

If you lose a transformer you can still operate at a reduced KVA

Question 26

Con of 3 single phase bank connected transformers

Answer 26

Harder to wire

Question 27

What degree of displacement is a wye to wye connection

Answer 27

0 degrees

Question 28

What degree displacement is a delta to delta connection

Answer 28

0 degrees

Question 29

What degree displacement is a wye to delta connection

Answer 29

30 degrees

Question 30

What degree displacement is a delta to wye connection

Answer 30

30 degrees

Question 31

What should your reading be in a wrongly connection wye secondary Three 120v phases

Answer 31

120v 120v 208v

Question 32

What should a delta connection read if it's connected properly

Answer 32

0volts

Question 33

What does it mean if voltage if half of a phase value in a delta

Answer 33

Voltage being produced by harmonics

Question 34

What should you read on a delta closure test if not wired correctly and each phase is 240v

Answer 34

240v 240v 480v

Question 35

A bank of three transformers is operated open delta until a new transformer arrives. The maximum percent of load available is?

Answer 35

57.7%

Question 36

In a 3phase 4 wire delta what is the voltage between phases A and neutral if the phase voltage is 240v

Answer 36

120x√3=208v

Question 37

Could a 3 phase 4 wire delta that supply's 120v 240v be rewired to produce 208/120

Answer 37

Yes

Question 38

What do laminated sheet cores do for the transformer

Answer 38

Limit Eddy currents

Question 39

What part of an open delta auto transformer that limits the total possible KVA for the load

Answer 39

The series coil

Question 40

What is the max KVA of two open delta auto transformers

Answer 40

17.32kva x 2

Question 41

What does permiability mean

Answer 41

Measure of how easily magnetic lines of force can pass through a material

Question 42

Causes of poor power quality

Answer 42

Line disturbances Non linear loads

Question 43

What kind of loads are linear

Answer 43

Heaters Hot water heater Baseboard heat Resistive loads

Question 44

What is the supply standard for frequency

Answer 44

+/- 5%

Question 45

What is the supply standard for voltage

Answer 45

+/- 10%

Question 46

Example of non linear loads

Answer 46

Electric welding Arc furnace Solid state recitfiers Personal computers Electric ballast lighting

Question 47

What kind of transformer is needed for linear loads

Answer 47

K1

Question 48

What kind of transformer is used for welders hid lights fluorescent lights

Answer 48

K4

Question 49

What kind of transformer is used for telecommunications Branch circuits in schools Healthcare

Answer 49

K13

Question 50

What kind of transformers are used for vfd, main frame computers, PC, computer terminals.

Answer 50

K20