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4th Year, Week 2 (Photovoltaic and Transformers) > Transformers Level 2 > Flashcards

Transformers Level 2 Flashcards

1
Q

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

A

Notch.

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2
Q

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

A

Reactance.

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3
Q

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

A

Saturable-Core

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4
Q

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

A

True.

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5
Q

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

A

3%

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6
Q

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

A

True.

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7
Q

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

A

Common-mode

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8
Q

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

A

Choke.

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9
Q

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

A

AC, DC

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10
Q

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

A
  1. ) Timing Signals

2. ) Equipment Activation.

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11
Q

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

A

50%

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12
Q

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

A

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

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13
Q

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

A

Output Reactors.

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14
Q

How is notching reduced?

A

By adding impedance.

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15
Q

How does adding impedance to the circuit affect notches?

A

It decreases their depth and makes them wider.

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16
Q

What three things does a drive-isolation transformer do?

A
  1. ) Reduces common-mode noise
  2. ) Reduces drive-induced ground currents.
  3. ) Changes voltage.
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17
Q

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

A

Reactance.

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18
Q

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

A

True.

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19
Q

Line Input Reactors are used in what three instances?

A
  1. ) Motor drive causes notches.
  2. ) Low impedance causes high inrush current.
  3. ) Capacitors are used for PF correction.
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20
Q

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

A

Power Quality

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21
Q

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

A

Reactor.

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22
Q

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

A

Autotransformer

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23
Q

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

A

The autotransformer

24
Q

What is the appeal of autotransformers over two winding?

A

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

25
Q

Which taps are connected to form an autotransformer?

A

H2 and X2

26
Q

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

A

True.

27
Q

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

A

Harmonics and Transient Voltages.

28
Q

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

A

True.

29
Q

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

A

10 Minutes on, 10 minutes off.

30
Q

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

A

Insulation.

31
Q

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

A

Down

32
Q

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

A

Up

33
Q

What are the three common uses for Autotransformers?

A
  1. ) Tap changing
  2. ) Starting of large synchronous and induction motors
  3. ) Variable Transformers
34
Q

Which autotransformer configuration is used for large machines?

A

Open Delta

35
Q

Which autotransformer configuration is used for smaller applications?

A

Wye

36
Q

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.

A

Variable.

37
Q

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

A

True

38
Q

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

A

50%, 65%, and 80%

39
Q

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

A

True

40
Q

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

A

True.

41
Q

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

A

60

42
Q

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

A

AC into DC

43
Q

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

A

Notch.

44
Q

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

A

3%

45
Q

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

A

Reactor.

46
Q

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

A

Reactors.

47
Q

What are the four different types of reactors?

A
  1. ) Line Reactors
  2. ) Output Reactors
  3. ) Saturable Core Reactors
  4. ) Chokes
48
Q

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

A

Saturation.

49
Q

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

A

Drive Isolation Transformer.

50
Q

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

A

Drive Isolation.

51
Q

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

A

5-25%

52
Q

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

A

True.

53
Q

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

A

Buck/Boost

54
Q

Buck/Boost transformers are typically __ Kva and smaller.

A

10

55
Q

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

A

True.

56
Q

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

A

True.

57
Q

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

A

False.

4th Year, Week 2 (Photovoltaic and Transformers) (2 decks)

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