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Transformers & PCB's > Transformers & PCB's > Flashcards

Transformers & PCB's Flashcards

1
Q

Made by connecting one end of each winding.

A

Wye connection

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2
Q

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

A

Currents

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3
Q

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

A

Higher

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4
Q

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

A

120

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5
Q

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

A

3

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6
Q

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

A

F, they are the same.

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7
Q

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

A

F, higher

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8
Q

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

A

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

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9
Q

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

A

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

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10
Q

Three phase watts (P) is calculated by:

A 
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)
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11
Q

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

A

T

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12
Q

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

A

Transformer

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13
Q

What are the 3 transformer classifications?

A

isolation transformer
autotransformer
current transformer

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14
Q

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

A

Yes

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15
Q

Turns ratio example:

A

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

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16
Q

N(P)

A

of turns in primary winding

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17
Q

N(S)

A

of turns in secondary winding

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18
Q

E(P)

A

Primary voltage

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19
Q

E(S)

A

Secondary voltage

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20
Q

I(P)

A

Primary current

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21
Q

I(S)

A

Secondary current

22
Q

Transformer formulas

A 
EP/ES = NP/NS
EP/ES = IS/IP
23
Q

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

A

Primary winding

24
Q

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

A

Secondary winding

25
Q

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

A

T

26
Q

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

A

Self-induction

27
Q

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

A

Excitation

28
Q

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

A

F, one

29
Q

What is a step-down transformer?

A

A transformer that has a lower secondary voltage than primary.

30
Q

What is a step-up transformer?

A

A transformer that has a secondary voltage than primary.

31
Q

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

A

power in must equal power out.

32
Q

Ratio formula

A

Ratio = E(S1)/E(P)

33
Q

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?

A

Distribution transformer

34
Q

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

A

Control transformer

35
Q

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

A

Autotransformers

36
Q

What is the output of an open delta?

A

86.6%

37
Q

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

A

Dielectric oil

38
Q

Why are windings 120 degrees apart?

A

So power does not go below zero

39
Q

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

A

phase; current

40
Q

What is the simplest circuit breaker?

A

Ordinary knife switch

41
Q

What is fundamental to the success of a circuit breaker?

A

Plasma arc

42
Q

How do air-blast breakers extinguish arc?

A

By a cooled dry air blast

43
Q

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

A

F, heated

44
Q

What is a circuit breakers primary function?

A

Protection

45
Q

What do you use to extinguish an arc?

A

Speed

46
Q

What are the 3 circuit breaker ratings?

A

Voltage class
Continuous current
Interrupting capacity
(or interrupting time)

47
Q

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

A

Continuous current rating

48
Q

How fast is interrupting time?

A

1/20th of a second

49
Q

What 3 methods can a breaker be tripped free?

A

Pneumatically
Mechanically
Electrically

50
Q

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

A

Harmonics

Transformers & PCB's (1 decks)

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