Transformer Principles

Question 1

Additive Polarity

Answer 1

Polarity where the H1 marking is opposite the X2 marking and the H2 marking is opposite the X1 marking.

Question 2

Delta Connection

Answer 2

The connection of a transformer to form a “Δ” configuration. Delta connections can be made by connecting odd to even terminals.

Question 3

Eddy Currents

Answer 3

Currents formed when the magnetic field induces currents in the iron core. This is reduced by the use of laminated cores to construct the transformer.

Question 4

Efficiency

Answer 4

Efficiency is always the ratio of output to input. It is the ratio of true (output power) to apparent (input power).

Question 5

Flux Leakage

Answer 5

Each transformer produces line of flux. Each time the transformer is energized there is some flux lost because of coupling.

Question 6

Hysteresis Losses

Answer 6

The result of the energy wasted in reversing the magnetization of the core every time the current reverses and magnetizes the core in a different direction.

Question 7

Kilovolt (KVA) Rating

Answer 7

The rating of a transformer in kilovolt-amps.

Question 8

Mutual Inductance

Answer 8

The effects of inductance are mutual between the primary and secondary. The current in the primary induces a voltage in the secondary.

Question 9

Open Delta

Answer 9

The connection of two transformers only. One side of the Delta is removed and the transformer is considered open.

Question 10

Polarity Markings

Answer 10

(+) = Positive and (-) = Negative.

Question 11

Primary Winding

Answer 11

The primary winding is the winding that is connected to the source voltage. It does not necessarily have to be the high voltage winding.

Question 12

Secondary Winding

Answer 12

The secondary winding is the winding that is connected to the load. It does not necessarily have to be the low voltage winding.

Question 13

Significance of 1.73

Answer 13

The multiplier from line to neutral in a 3-phase transformer. Example: A 3-phase “Y” to neutral—208 volts divided by 1.73 equals 120 volts.

Question 14

Subtractive Polarity

Answer 14

Polarity where the H1 terminal is opposite the X1 terminal and the H2 terminal is opposite the X2 terminal.

Question 15

Transformer Polarity

Answer 15

A system of (ANSI) markings of the transformer leads. The high voltage leads are “H” leads and the low voltage leads are “X” leads.

Question 16

Turns Ratio

Answer 16

The ratio of the turns in the primary to the turns in the secondary.

Question 17

Wye Connection

Answer 17

The connection of transformer to form a “Y” configuration. “Y” connections can be made by connecting either the even terminals or the odd terminals together.

Question 18

Core Type Transformer

Answer 18

The iron core is used to concentrate the lines of force and produce a better magnetic coupling between the two coils.

Question 19

Shell Type Transformer

Answer 19

Made up of silicon steel laminations covered with varnish and pressed together. The windings are wound in layers and fit over the center section of the core. The laminated core helps reduce the power losses due to eddy currents and hysteresis, and also reduces flux leakage.

Question 20

Step-up Transformer

Answer 20

Contains more conductors to be cut by the magnetic field, thus a greater amount of voltage will be induced into the secondary than was applied to the primary. It will increase the voltage.

Question 21

Step-down Transformer

Answer 21

Contains less conductor to be cut by the magnetic field, thus a smaller amount of voltage will be induced into the secondary than was applied to the primary. It will decrease the voltage

Question 22

Isolation Transformers

Answer 22

A transformer of the multiple-winding type, with the primary and secondary windings physically separated, which inductively couples its secondary winding to the grounded feeder systems that energize its primary winding.

Question 23

Subtractive Transformer

Answer 23

The H1 and X1 leads are directly across from each other.

Question 24

Additive Transformer

Answer 24

The H1 and X1 leads of a transformer with additive polarity are diagonally across from each other.

Question 25

When paralleling two single-phase transformers, the conditions that must be met are:

Answer 25

Have the same voltage ratings.
Polarities must be correct.
Same percent of impedance.

Question 26

Polarity Testing

Answer 26

A procedure that verifies that electrical conductors are connected to the correct terminals and are not reversed.

Question 27

Primary Winding

Answer 27

The winding that receives the power from the source.

Question 28

Secondary Winding

Answer 28

The winding into which transformed voltage is induced.

Question 29

Single winding transformers have high voltage winding leads marked ___ and ___.

Answer 29

H1, H2

Question 30

Single winding transformers have low voltage winding leads marked ___ and ___.

Answer 30

X1, X2

Question 31

Dual winding transformers have the high voltage winding leads marked…

Answer 31

H1, H2, H3, and H4

Question 32

Dual winding transformers have the low voltage winding leads marked…

Answer 32

X1, X2, X3, and X4

Question 33

Subtractive Transformer

Answer 33

If the X1 terminal is directly across from the H1 terminal so it has subtractive polarity.

Question 34

Additive Transformer

Answer 34

If the X1 terminal sits diagonally across from the H1 terminal so it has additive polarity.

Question 35

When paralleling two single-phase transformers, they must have…

Answer 35

same voltage, same percentage of impedance, and correct polarities.

Question 36

Impedance (Z)

Answer 36

Represented by the symbol Z, is a measure of the opposition to electrical flow.

Question 37

Percent Impedance (%Z)

Answer 37

The percent of the rated load impedance possessed by a transformer.

Question 38

Transformers may have more than one winding on the high voltage and/or low voltage side. True or false?

Answer 38

True

Question 39

Autotransformer

Answer 39

A single-winding transformer with a single winding mounted on an iron core with the primary and secondary currents flowing in parts of the same winding.

Question 40

Control Transformer

Answer 40

A small transformer similar in construction to power or distribution transformer and are used to transform a higher voltage to a safer lower voltage, for electrical control devices.

Question 41

Current Transformer (CT)

Answer 41

Used to step down a relatively high current to some low value for the operation of instruments and some control devices.

Question 42

Tap

Answer 42

A device that attaches a branch circuit to a main circuit, a threading tool, or a conductor that combines multiple sized conductors.

Question 43

There is a possibility for backfeed in which case voltage would feed back through the line making what was the secondary now the primary winding. True or false?

Answer 43

True