Principles Of AC Circuits 030201d Flashcards
How does resistance in an ac circuit compare to a dc circuit?
The calculated value for resistance in an ac circuit is often higher than in a dc circuit due to additional factors.
What is the term used for the resistance of a component in an ac circuit?
The term is effective or ac resistance.
What is the ohmic or dc resistance?
It is the measured value of resistance.
What are the factors that contribute to ac resistance?
The five factors are:
1. dc or Ohmic Resistance
2. Eddy Current & hysteresis (Iron losses)
3. Dielectric
4. Skin Effect.
What factors affect resistance in a dc circuit?
Material of the conductor.
Cross-sectional area of the conductor.
Length of the conductor.
Temperature.
What are iron losses?
It is the combination of hysteresis losses and eddy current losses.
What is hysteresis losses?
It is the energy used to reverse the polarity of the magnetic domains in a magnetic material.
What do manufactures do to reduce hysteresis losses?
Use an alloy containing silicon for the core and armature material.
Silicon reduces molecular friction and allows magnetic domains to rearrange easier.
What are eddy currents?
Circulating currents induced in any metallic material that is adjacent to an ac circuits expanding and collapsing magnetic field.
How can eddy currents be reduced?
Can be reduced by constructing cores and armatures out of thin sheets of material called laminations.
What is dielectric losses?
The energy lost to a circuit, caused by voltage stress on the insulation of a conductor.
What is skin effect?
The tendency of alternating current to flow close to the surface of a conductor due to the induced CEMF being greater in the central core.
Does skin effect get better or worse with higher frequencies?
Skin effect is greater as frequencies increase.
What is impedance?
The total opposition to the flow of current in an ac circuit.
What are the three factors that affect impedance in an AC circuit?
Resistance.
Inductive reactance.
Capacitive reactance.
What is inductance?
Opposes a change in current.
What is capacitance?
Opposes a change in voltage.
What is inductive and capacitive reactance?
Circuit properties that limit the total amount of current in an AC circuit.
How is impedance calculated?
Right-angle triangles.
Trigonometric functions.
Pythagorean theorem.
What are the 3 sides of a triangle called?
Vertical side - altitude.
Horizontal side - base.
Long side - hypotenuse.
What degree do 3 three angles of a triangle always add up to?
180 degrees.
What is the formula for Pythagorean theorem?
A^2(altitude) + b^2(base) = C^2(hypotenuse)
For an impedance triangle, what is represented by each side of the triangle?
Horizontal side - Resistance (R)
Vertical side - Reactance (X)
Hypotenuse - Impedance (Z)
