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Test Prep > Transformer Theory > Flashcards

Transformer Theory Flashcards

1
Q

What is permeability?

A

The ease at which iron conducts magnetic flux

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2
Q

Purpose of a core within a TX?

A

To direct and channel the magnetic field.

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3
Q

What is the core made of within a TX?

A

Thin laminated iron sheets.

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4
Q

The primary coil has _____ turns, ______ wire, ______ insulation

A

More, smaller, higher

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5
Q

Two main losses within a TX?

A

Copper loss and core loss

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6
Q

Two purposes for taps?

A

1) to correct primary voltage
2) to control voltage to a customer

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7
Q

Taps are installed on the __________?

A

Primary coil

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8
Q

The highest taps on a TX are labeled __ , __ , or __

A

1, I, or A

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9
Q

Four methods of cooling a TX?

A

1) fans
2) fins
3) air
4) oil

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10
Q

What year were PCBs banned?

A

1979

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11
Q

What does PCB stand for?

A

Polychlorinated Biphenyl

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12
Q

Copper loss come from what?

A

Resistance of the coils and heat loss

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13
Q

Iron loss comes from eddy currant losses, a product of ________?

A

The constant reversing of the magnetic field

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14
Q

Symbol for impedance is ___?

A

%Z

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15
Q

Polarity is ___________?

A

Direction of currant flow

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16
Q

When H1 and X1 bushings are on the same side the TX is ________?

A

Subtractive

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17
Q

Tx rated over _____KVA or voltage over ______ are subtractive

A

200 KVA
8,600 v

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18
Q

Two main enemies of transformers?

A

High voltage surges
Heating

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19
Q

The fuse protects the TX from ____?

A

Current surges

20
Q

Arrestors protect the transformer from ______?

A

Voltage surges

21
Q

Two types of arresters are ______ and ______?

A

Expulsion
Valve

22
Q

How does a wye-delta open bank share 3-phase load

A

Equally at 57.7%

23
Q

How does a Y-Y closed bank share 3-phase load?

A

1/3 each

24
Q

How does a Y-delta closed bank share single phase load?

A

1/3, 2/3, 1/3

25
Q

How does a Y-Y closed bank share single phase load?

A

1/3 each

26
Q

Electric currant is _________?

A

The flow of electrons in a conductor

27
Q

Strength of a electro magnetic field in a TX depend on what?

A

-amount of current flowing
-number of turns in the windings
- permeability of core

28
Q

Once voltage is induced in a conductor, what else is required before current will flow?

A

Circuit must be closed or completed

29
Q

How does a closed Y-Y bank share load?

A

3[] ——1/3 each
1[] ——1/3 each

30
Q

How does a closed Y-Delta bank share load?

A

3(/) equally at 57.7%
1(/). 1/3 power pot, 2/3 lighter pot, 1/3 power pot

31
Q

How does a Y-Delta Open bank share load ?

A

3(/) equally at 57.7% of total kva
1(/) 100% lighter pot

32
Q

If the nameplate shows an X between primary voltages means___________?

A

The coil may be put in series or parallel, but never center tapped

33
Q

What does it mean if there is a slash (/) between the primary voltages on a nameplate?

A

Both H1 and H2 are insulated
Suitable for delta connection

34
Q

If the nameplate conveys 120/240 what can that mean?

A

The coil can be connected in series, parallel, or center tapped series

35
Q

If the nameplate conveys the secondary 240/120 or 208/120 what does that mean?

A

Coils are permanently connected in center tapped series, and can not be paralleled

36
Q

Definition of a neutral?

A

A currant carrying conductor at or near ground potential that acts as a return for unbalanced load.

37
Q

Two main enemies of TX’s are what?

A

-high voltage surge from lightning
-Heating caused by overloading

38
Q

Reactive power comes from _________?
And can be corrected by the use of ___________?

A

-Motor load
-Capacitors

39
Q

How many steps are in a tap changer TX, what percentage is each step?

A

5 steps
2.5% each step

40
Q

3 main parts of a TX?

A

Core coil can

41
Q

Definition of a watt

A

The power of 1 amp flowing under the pressure of 1 volt

42
Q

What is the advantage of a Wye secondary?

A

Balanced load, more efficient

43
Q

Why do we float the primary neutral on a Wye-Delta closed bank

A

If neutral bus becomes grounded, and a TX fuse is blown, the bank will still produce proper voltage but capacity will be reduced to 57.7% —> leading to future failure

44
Q

If a neutral bus is grounded on a Wye-Delta closed bank, and a primary line fuse is opened what happens?

A

The TX connected to the dead line will act as a step up and back feed the “dead” line

45
Q

When a TX fuse is blown on a Wye-Delta closed bank what occurs with the floated neutral?

A

Will be at half the phase voltage

46
Q

What is a transformer?

A

A magneticly coupled ratio device that operates on the principle of mutual induction

47
Q

What is a ground?

A

An artificial electrical connection to earth

Test Prep (2 decks)

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