Transformers & PCB's

Question 1

Made by connecting one end of each winding.

Answer 1

Wye connection

Question 2

Line and phase ____ are the same in a wye connection.

Answer 2

Currents

Question 3

In a wye-connected system, the line voltage is higher/lower than the phase voltage by 1.732.

Answer 3

Higher

Question 4

Three-phase voltages are ____ degrees out of phase with each other.

Answer 4

120

Question 5

Delta connections are made by ____ separate inductive loads being connected.

Answer 5

3

Question 6

T/F In a delta connection, line and phase voltages are different.

Answer 6

F, they are the same.

Question 7

T/F In a delta connected system, the line current is lower than the phase current by 1.732.

Answer 7

F, higher

Question 8

If line values of voltage (E) and current (I) are known, apparent power is calculated by:

Answer 8

VA = 1.732 x E (line) x I (line)

Question 9

If phase values of voltage (E) and current (I) are known, apparent power is calculated by:

Answer 9

VA = 3 x E (phase) x I (phase)

Question 10

Three phase watts (P) is calculated by:

Answer 10

P = 1.732 x E (line) x I (line) x PF
(PF = 1 unless otherwise stated)

P = 3 x E (phase) x I (phase) x PF
(PF = 1 unless otherwise stated)

Question 11

T/F Wye connections are characterized by the fact that 1 terminal of each of the devices is connected together.

Answer 11

T

Question 12

What is a magnetically operated machine that can change values of voltage, current and impedance without a change of frequency?

Answer 12

Transformer

Question 13

What are the 3 transformer classifications?

Answer 13

isolation transformer
autotransformer
current transformer

Question 14

Are all values of a transformer proportional to its turns ratio?

Answer 14

Yes

Question 15

Turns ratio example:

Answer 15

4:1 means 4 turns of primary winds to 1 secondary wind

Question 16

N(P)

Answer 16

of turns in primary winding

Question 17

N(S)

Answer 17

of turns in secondary winding

Question 18

E(P)

Answer 18

Primary voltage

Question 19

E(S)

Answer 19

Secondary voltage

Question 20

I(P)

Answer 20

Primary current

Question 21

I(S)

Answer 21

Secondary current

Question 22

Transformer formulas

Answer 22

EP/ES = NP/NS
EP/ES = IS/IP

Question 23

Where is the power input winding connected to incoming power supply (generator side)?

Answer 23

Primary winding

Question 24

Where is the load or output winding connected to driven load?

Answer 24

Secondary winding

Question 25

T/F In an isolation transformer, the secondary winding is physically and electrically isolated from primary winding.

Answer 25

T

Question 26

What is it called when a coil induced a voltage into itself?

Answer 26

Self-induction

Question 27

The ____ current is the amount of current required to magnetize the core of the transformer.

Answer 27

Excitation

Question 28

T/F Mutual induction is the ability of two coils to induce a voltage into another coil.

Answer 28

F, one

Question 29

What is a step-down transformer?

Answer 29

A transformer that has a lower secondary voltage than primary.

Question 30

What is a step-up transformer?

Answer 30

A transformer that has a secondary voltage than primary.

Question 31

A good rule of thumb for any type of transformer is that:

Answer 31

power in must equal power out.

Question 32

Ratio formula

Answer 32

Ratio = E(S1)/E(P)

Question 33

What transformer changes high voltage of power company distribution lines to the common 240/120 volts used to supply power to most homes and many business?

Answer 33

Distribution transformer

Question 34

What transformer reduces line voltage to the value needed to operate control circuits?

Answer 34

Control transformer

Question 35

These one-winding transformers use same winding for both the primary and secondary.

Answer 35

Autotransformers

Question 36

What is the output of an open delta?

Answer 36

86.6%

Question 37

What provides electric insulation between the windings and the case, helps provide cooling and to prevent moisture formation which can deteriorate the winding insulation?

Answer 37

Dielectric oil

Question 38

Why are windings 120 degrees apart?

Answer 38

So power does not go below zero

Question 39

Only ____ values of voltage and _____ can be used when calculating transformer values.

Answer 39

phase; current

Question 40

What is the simplest circuit breaker?

Answer 40

Ordinary knife switch

Question 41

What is fundamental to the success of a circuit breaker?

Answer 41

Plasma arc

Question 42

How do air-blast breakers extinguish arc?

Answer 42

By a cooled dry air blast

Question 43

T/F Sulfur hexafluoride must be kept cool if the circuit breaker will be used outdoors

Answer 43

F, heated

Question 44

What is a circuit breakers primary function?

Answer 44

Protection

Question 45

What do you use to extinguish an arc?

Answer 45

Speed

Question 46

What are the 3 circuit breaker ratings?

Answer 46

Voltage class
Continuous current
Interrupting capacity
(or interrupting time)

Question 47

What is the current that the breaker will carry indefinitely without exceeding a specified temperature rise?

Answer 47

Continuous current rating

Question 48

How fast is interrupting time?

Answer 48

1/20th of a second

Question 49

What 3 methods can a breaker be tripped free?

Answer 49

Pneumatically
Mechanically
Electrically

Question 50

What are currents that operate at a frequency that is a multiple of a fundamental power of frequency?

Answer 50

Harmonics