Transformers Level 2 Flashcards
A ? is a distortion in a voltage waveform where the voltage quickly drops toward zero and then returns to the correct value.
Notch.
____ is the opposition to current flow that is only present in AC power.
Reactance.
A ____-type reactor is basically the primary and secondary being wrapped around the same iron core.
Saturable-Core
T/F: Electric motors typically draw many times their full-load current during startup.
True.
To reduce notch depth to about 50%, a reactor should have about __% impedance.
3%
T/F: All two-winding transformers are isolation transformers.
True.
A type of electromagnetic interference on power or communication lines is called ____ noise.
Common-mode
A reactor used to reduce common-mode noise is called a common-mode ____.
Choke.
In a saturable-core reactor, large amounts of ___ current can be controlled by a small amount of ___ current.
AC, DC
What two things are ‘Zero-Crossovers’ usually used for?
- ) Timing Signals
2. ) Equipment Activation.
How much must notch depth be reduced (in a percentage) to eliminate extra ‘zero-crossovers’, (which cause problems)?
50%
T/F: A saturable-core reactor has only one winding.
False. Its has two, though they are wrapped around the same core.
____ help eliminate voltage spikes by slowing down the rate of change in the drive output voltage.
Output Reactors.
How is notching reduced?
By adding impedance.
How does adding impedance to the circuit affect notches?
It decreases their depth and makes them wider.
What three things does a drive-isolation transformer do?
- ) Reduces common-mode noise
- ) Reduces drive-induced ground currents.
- ) Changes voltage.
Do reduce power quality problems due to non-linear loads, ____ is added to the circuit.
Reactance.
T/F: The secondary of a drive isolation transformer represents a separately derived system.
True.
Line Input Reactors are used in what three instances?
- ) Motor drive causes notches.
- ) Low impedance causes high inrush current.
- ) Capacitors are used for PF correction.
Nonlinear rectified power supplies are a common cause of ____ problems.
Power Quality
Simply put, A ____ is a coil added in series with a load to reduce inrush current, voltage notching effects, and voltage spikes.
Reactor.
A(n) ____ is any transformer in which the primary and secondary circuits have a portion of their two windings in common.
Autotransformer
Which has a lower impedance, a two-winding transformer or an autotransformer?
The autotransformer
What is the appeal of autotransformers over two winding?
Their is only one coil so it takes much less copper to manufacture, therefore making it much cheaper.
Which taps are connected to form an autotransformer?
H2 and X2
T/F: An autotransformer has a higher power rating than an equivalent two-winding transformer.
True.
Autotransformers aren’t able to block the flow of what two things in a three-phase system.
Harmonics and Transient Voltages.
T/F: Autotransformers are designed to be overloaded during motor starting.
True.
What is a typical duty cycle for allowing the cool down of an autotransformer?
10 Minutes on, 10 minutes off.
The cost of ____ makes extremely large autotransformers not financially viable.
Insulation.
For a step-____ autotransformer, the source is applied across the entire coil.
Down
For a step-____ autotransformer, the source is applied across only part of the coil.
Up
What are the three common uses for Autotransformers?
- ) Tap changing
- ) Starting of large synchronous and induction motors
- ) Variable Transformers
Which autotransformer configuration is used for large machines?
Open Delta
Which autotransformer configuration is used for smaller applications?
Wye
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.
Variable.
T/F: When using an autotransformer for starting motors, the voltage and current are NOT equal.
True
What are the three common percentages to reduce line voltage to for reduced voltage starting with an Autotransformer?
50%, 65%, and 80%
T/F: Reducing voltage during motor starting also results in reduced current and torque.
True
T/F: In a variable transformer, it is possible to move the contact under load without interrupting the circuit.
True.
AC power in the United States is generated and distributed at __Hz.
60
A rectifier in the most basic terms, coverts ___ voltage into ___ voltage.
AC into DC
A ___ is a significant drop in voltage at random times in the AC sinewave.
Notch.
__% impedance is usually the correct amount to fix notching, by reducing the depth of notches by 50%.
3%
A ____ is a coil in series with the load and source.
Reactor.
____ resist current from the source becoming too high and keep it at a constant level.
Reactors.
What are the four different types of reactors?
- ) Line Reactors
- ) Output Reactors
- ) Saturable Core Reactors
- ) Chokes
____ is a condition of an iron core when any more magnetization will not make the core more magnetic.
Saturation.
Any transformer that is not an autotransformer is a(n) ____ transformer.
Drive Isolation Transformer.
Which is built heavier and more sturdy? Drive Isolation Transformers or Isolation Transformers?
Drive Isolation.
Buck/Boost Transformers usually change the voltage by ___-___%
5-25%
T/F: Buck/Boost Transformers usually have two primaries and two secondaries.
True.
____ transformers are wired like autotransformers but in different orientations to either add or subtract voltages.
Buck/Boost
Buck/Boost transformers are typically __ Kva and smaller.
10
T/F: Buck/Boost transformers can sometimes be used as isolating transformers.
True.
T/F: Both the primaries and secondaries of buck/boost transformers are dual voltage.
True.
T/F: The length of a conductor does not significantly impact voltage drop on the line.
False.
