Transformers Level 2

Question 1

A ? is a distortion in a voltage waveform where the voltage quickly drops toward zero and then returns to the correct value.

Answer 1

Notch.

Question 2

____ is the opposition to current flow that is only present in AC power.

Answer 2

Reactance.

Question 3

A ____-type reactor is basically the primary and secondary being wrapped around the same iron core.

Answer 3

Saturable-Core

Question 4

T/F: Electric motors typically draw many times their full-load current during startup.

Answer 4

True.

Question 5

To reduce notch depth to about 50%, a reactor should have about __% impedance.

Answer 5

3%

Question 6

T/F: All two-winding transformers are isolation transformers.

Answer 6

True.

Question 7

A type of electromagnetic interference on power or communication lines is called ____ noise.

Answer 7

Common-mode

Question 8

A reactor used to reduce common-mode noise is called a common-mode ____.

Answer 8

Choke.

Question 9

In a saturable-core reactor, large amounts of ___ current can be controlled by a small amount of ___ current.

Answer 9

AC, DC

Question 10

What two things are ‘Zero-Crossovers’ usually used for?

Answer 10

1. ) Timing Signals

2. ) Equipment Activation.

Question 11

How much must notch depth be reduced (in a percentage) to eliminate extra ‘zero-crossovers’, (which cause problems)?

Answer 11

50%

Question 12

T/F: A saturable-core reactor has only one winding.

Answer 12

False. Its has two, though they are wrapped around the same core.

Question 13

____ help eliminate voltage spikes by slowing down the rate of change in the drive output voltage.

Answer 13

Output Reactors.

Question 14

How is notching reduced?

Answer 14

By adding impedance.

Question 15

How does adding impedance to the circuit affect notches?

Answer 15

It decreases their depth and makes them wider.

Question 16

What three things does a drive-isolation transformer do?

Answer 16

1. ) Reduces common-mode noise
2. ) Reduces drive-induced ground currents.
3. ) Changes voltage.

Question 17

Do reduce power quality problems due to non-linear loads, ____ is added to the circuit.

Answer 17

Reactance.

Question 18

T/F: The secondary of a drive isolation transformer represents a separately derived system.

Answer 18

True.

Question 19

Line Input Reactors are used in what three instances?

Answer 19

1. ) Motor drive causes notches.
2. ) Low impedance causes high inrush current.
3. ) Capacitors are used for PF correction.

Question 20

Nonlinear rectified power supplies are a common cause of ____ problems.

Answer 20

Power Quality

Question 21

Simply put, A ____ is a coil added in series with a load to reduce inrush current, voltage notching effects, and voltage spikes.

Answer 21

Reactor.

Question 22

A(n) ____ is any transformer in which the primary and secondary circuits have a portion of their two windings in common.

Answer 22

Autotransformer

Question 23

Which has a lower impedance, a two-winding transformer or an autotransformer?

Answer 23

The autotransformer

Question 24

What is the appeal of autotransformers over two winding?

Answer 24

Their is only one coil so it takes much less copper to manufacture, therefore making it much cheaper.

Question 25

Which taps are connected to form an autotransformer?

Answer 25

H2 and X2

Question 26

T/F: An autotransformer has a higher power rating than an equivalent two-winding transformer.

Answer 26

True.

Question 27

Autotransformers aren't able to block the flow of what two things in a three-phase system.

Answer 27

Harmonics and Transient Voltages.

Question 28

T/F: Autotransformers are designed to be overloaded during motor starting.

Answer 28

True.

Question 29

What is a typical duty cycle for allowing the cool down of an autotransformer?

Answer 29

10 Minutes on, 10 minutes off.

Question 30

The cost of ____ makes extremely large autotransformers not financially viable.

Answer 30

Insulation.

Question 31

For a step-____ autotransformer, the source is applied across the entire coil.

Answer 31

Down

Question 32

For a step-____ autotransformer, the source is applied across only part of the coil.

Answer 32

Up

Question 33

What are the three common uses for Autotransformers?

Answer 33

1. ) Tap changing 2. ) Starting of large synchronous and induction motors 3. ) Variable Transformers

Question 34

Which autotransformer configuration is used for large machines?

Answer 34

Open Delta

Question 35

Which autotransformer configuration is used for smaller applications?

Answer 35

Wye

Question 36

A(n) ____ transformer is a continuously adjustable autotransformer consisting of a single layer of wire wound on a toroidal core, and a carbon brush that traverses this winding.

Answer 36

Variable.

Question 37

T/F: When using an autotransformer for starting motors, the voltage and current are NOT equal.

Answer 37

True

Question 38

What are the three common percentages to reduce line voltage to for reduced voltage starting with an Autotransformer?

Answer 38

50%, 65%, and 80%

Question 39

T/F: Reducing voltage during motor starting also results in reduced current and torque.

Answer 39

True

Question 40

T/F: In a variable transformer, it is possible to move the contact under load without interrupting the circuit.

Answer 40

True.

Question 41

AC power in the United States is generated and distributed at __Hz.

Answer 41

60

Question 42

A rectifier in the most basic terms, coverts ___ voltage into ___ voltage.

Answer 42

AC into DC

Question 43

A ___ is a significant drop in voltage at random times in the AC sinewave.

Answer 43

Notch.

Question 44

__% impedance is usually the correct amount to fix notching, by reducing the depth of notches by 50%.

Answer 44

3%

Question 45

A ____ is a coil in series with the load and source.

Answer 45

Reactor.

Question 46

____ resist current from the source becoming too high and keep it at a constant level.

Answer 46

Reactors.

Question 47

What are the four different types of reactors?

Answer 47

1. ) Line Reactors 2. ) Output Reactors 3. ) Saturable Core Reactors 4. ) Chokes

Question 48

____ is a condition of an iron core when any more magnetization will not make the core more magnetic.

Answer 48

Saturation.

Question 49

Any transformer that is not an autotransformer is a(n) ____ transformer.

Answer 49

Drive Isolation Transformer.

Question 50

Which is built heavier and more sturdy? Drive Isolation Transformers or Isolation Transformers?

Answer 50

Drive Isolation.

Question 51

Buck/Boost Transformers usually change the voltage by ___-___%

Answer 51

5-25%

Question 52

T/F: Buck/Boost Transformers usually have two primaries and two secondaries.

Answer 52

True.

Question 53

____ transformers are wired like autotransformers but in different orientations to either add or subtract voltages.

Answer 53

Buck/Boost

Question 54

Buck/Boost transformers are typically __ Kva and smaller.

Answer 54

10

Question 55

T/F: Buck/Boost transformers can sometimes be used as isolating transformers.

Answer 55

True.

Question 56

T/F: Both the primaries and secondaries of buck/boost transformers are dual voltage.

Answer 56

True.

Question 57

T/F: The length of a conductor does not significantly impact voltage drop on the line.

Answer 57

False.