Unit 22

Question 1

What is used to reduce losses because of eddy currents in transformers? and what is used to separate them?

Answer 1

Long laminated iron cores ; insulation (usually lacquer)

Question 2

The relationship of the primary winding voltage to the secondary winding voltage is the same as the relationship between the ________ on the primary as compared to the ________ on the secondary

Answer 2

Number of turns ; Number of turns

Question 3

This device has the ability to transfer electrical energy from one system to another, with no physical connection between the two systems

Answer 3

Transformer

Question 4

1 kilovolt-ampere = how many VA?

Answer 4

1,000

Question 5

What do you call the energy required to realign the core molecules to the changing electromagnetic field in a transformer?

Answer 5

Hysteresis Loss

Question 6

Conductor resistance is directly proportional to the ____ of a conductor and inversely proportional to the _____ of a conductor

Answer 6

Length ; Cross Sectional Area

Question 7

The voltage level that can be induced in the secondary winding, form the primary magnetic field, is a function of the number of secondary conductor loops (turns) that are ____ by the primary electromagnetic field

Answer 7

Cut

Question 8

What is the main purpose of an autotransformer?

Answer 8

Step voltage up or down

Question 9

The energy transfer of a transformer is accomplished because the ______ lines of force from the primary winding induce a _____ in the secondary wnding

Answer 9

Electromagnetic ; Voltage

Question 10

Autotransformers use a common _____ for both the primary and secondary.

Answer 10

Winding

Question 11

The induced voltage in each loop of the secondary winding is dependent on the number of secondary conductor loops as compared to what?

Answer 11

The number of primary turns

Question 12

The secondary winding of a step-down transformer has ____ turns than the primary winding.

Answer 12

Fewer

Question 13

As current flows through the transformer, the iron core is temporarily ____ by the electromagnetic field created by the alternating current

Answer 13

Magnetized

Question 14

The heating from harmonic currents is _______ to the square of the harmonic current

Answer 14

Proportional

Question 15

The primary winding in a transformer is connected to the _____ and the secondary winding is connected to the _____

Answer 15

Voltage source ; Load

Question 16

The disadvantage of an autotransformer is the lack of ____ between the primary and secondary conductors.

Answer 16

Isolation

Question 17

Voltage induced in the secondary winding of a transformer is equal to the sum of what?

Answer 17

Voltages induced in each loop of the secondary winding

Question 18

When a load is connected to the secondary of a transformer, secondary voltage induced from the primary magnetic field will cause _____ to flow through the secondary conductor wiinding

Answer 18

Current

Question 19

Three-phase, 4-wire, wye-connected systems that supply nonlinear line-to-neutral loads can ______ because of circulating odd triplen ______ currents.

Answer 19

Overheat ; Harmonic

Question 20

What is the formula for calculating a single-phase transformers primary and secondary current rating?

Answer 20

I = VA / E

Question 21

The _____ lines from the secondary magnetic field effectively reduce the strength of the primary flux lines, and as a result, less CEMF is generated in the primary winding conductors.

Answer 21

Flux

Question 22

The secondary current flow in the secondary winding creates an ______ field that opposes the primary electromagnetic field

Answer 22

Electromagnetic

Question 23

Name four types of power losses that occur in transformers

Answer 23

Conductor Resistance ; Hysteresis ; Eddy Currents ; Flux Leakage

Question 24

What is the formula for calculating a three-phase transformers primary and secondary current rating?

Answer 24

I = VA / (E x 1.732)

Question 25

The leakage of the electromagnetic flux lines between the ____ and ____ also represents wasted energy

Answer 25

Primary ; Secondary

Question 26

The secondary winding of a step-up transformer has ___ turns than the primary winding.

Answer 26

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