Total Material Flashcards
What are harmonics?
Distortions to the voltage and current waveforms from their normal sinusoidal shape
Harmonics are similar to electrical noise (T/F)
False. Harmonics are not similar to electrical noise. They are a steady state problem.
Harmonics are usually a steady state problem. What does this mean?
If harmonics are present, then they are always present.
What are the 2 sources that harmonics come from?
- Solid State devices
- Lighting
What type of solid state devices produce harmonics?
1.SCR
2. Thyristors
What type of lighting produces harmonics?
Lighting equipped with ballasts
What tends to magnify harmonics?
PFCE
There are 2 ways of dealing with harmonics. What is the first?
Isolation
There are 2 ways of dealing with harmonics. What is the second?
Improving power quality
What are the methods of isolation to deal with harmonics?
Isolation transformers
Uninterruptible Power Supplies (UPS)
What are the methods of improving power quality?
Using shunt and series filters.
In the presence of harmonic currents, motors will run at a higher or lower temperature?
Higher.
Why do harmonics have the ability to produce mechanical vibrations and noise?
Harmonics can produce torque pulsations.
Electronic equipment often requires an accurate voltage and current waveform. How do harmonics affect these waveforms?
Harmonics distort the waveform by reducing its magnitude, and misshaping the wave.
What is another word for shunt filter?
High pass filter
What is another word for series filter?
Low pass filter
How can we control both voltage and frequency over a large range?
Use a VFD
VFD stands for:
Variable Frequency Drive
In the VFD, the converter is a ________ that is either _________ or ___________
- Rectifier
- Uncontrolled using diodes
- Controlled using SCRs
A converter has 2 voltage types. These are ____ and _____
Fixed and Variable DC (Link) Voltage
What is the purpose of the DC link in a VFD?
Filter out the DC link ripple voltage using an inductor or capacitor
What is the purpose of the inverter in a VFD?
Uses the DC link voltage to provide a variable AC voltage and Frequency to the motor at a constant volts/hertz ratio
What are 3 advantages of using VFDs?
- Control speed over large range
- Start the same load at different speeds safely
- The motor will run cooler than if we reduce voltage only
What are the disadvantages of VFDs?
Expensive
More components to maintain
More heat generation
