Transformer Theory

Question 1

What is permeability?

Answer 1

The ease at which iron conducts magnetic flux

Question 2

Purpose of a core within a TX?

Answer 2

To direct and channel the magnetic field.

Question 3

What is the core made of within a TX?

Answer 3

Thin laminated iron sheets.

Question 4

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

Answer 4

More, smaller, higher

Question 5

Two main losses within a TX?

Answer 5

Copper loss and core loss

Question 6

Two purposes for taps?

Answer 6

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

Question 7

Taps are installed on the __________?

Answer 7

Primary coil

Question 8

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

Answer 8

1, I, or A

Question 9

Four methods of cooling a TX?

Answer 9

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

Question 10

What year were PCBs banned?

Answer 10

1979

Question 11

What does PCB stand for?

Answer 11

Polychlorinated Biphenyl

Question 12

Copper loss come from what?

Answer 12

Resistance of the coils and heat loss

Question 13

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

Answer 13

The constant reversing of the magnetic field

Question 14

Symbol for impedance is ___?

Answer 14

%Z

Question 15

Polarity is ___________?

Answer 15

Direction of currant flow

Question 16

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

Answer 16

Subtractive

Question 17

Tx rated over _____KVA or voltage over ______ are subtractive

Answer 17

200 KVA
8,600 v

Question 18

Two main enemies of transformers?

Answer 18

High voltage surges
Heating

Question 19

The fuse protects the TX from ____?

Answer 19

Current surges

Question 20

Arrestors protect the transformer from ______?

Answer 20

Voltage surges

Question 21

Two types of arresters are ______ and ______?

Answer 21

Expulsion
Valve

Question 22

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

Answer 22

Equally at 57.7%

Question 23

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

Answer 23

1/3 each

Question 24

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

Answer 24

1/3, 2/3, 1/3

Question 25

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

Answer 25

1/3 each

Question 26

Electric currant is _________?

Answer 26

The flow of electrons in a conductor

Question 27

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

Answer 27

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

Question 28

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

Answer 28

Circuit must be closed or completed

Question 29

How does a closed Y-Y bank share load?

Answer 29

3[\] ——1/3 each 1[\] ——1/3 each

Question 30

How does a closed Y-Delta bank share load?

Answer 30

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

Question 31

How does a Y-Delta Open bank share load ?

Answer 31

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

Question 32

If the nameplate shows an X between primary voltages means___________?

Answer 32

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

Question 33

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

Answer 33

Both H1 and H2 are insulated Suitable for delta connection

Question 34

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

Answer 34

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

Question 35

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

Answer 35

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

Question 36

Definition of a neutral?

Answer 36

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

Question 37

Two main enemies of TX’s are what?

Answer 37

-high voltage surge from lightning -Heating caused by overloading

Question 38

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

Answer 38

-Motor load -Capacitors

Question 39

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

Answer 39

5 steps 2.5% each step

Question 40

3 main parts of a TX?

Answer 40

Core coil can

Question 41

Definition of a watt

Answer 41

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

Question 42

What is the advantage of a Wye secondary?

Answer 42

Balanced load, more efficient

Question 43

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

Answer 43

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

Question 44

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

Answer 44

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

Question 45

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

Answer 45

Will be at half the phase voltage

Question 46

What is a transformer?

Answer 46

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

Question 47

What is a ground?

Answer 47

An artificial electrical connection to earth