103G Fundamentals of Alternating Current Flashcards
The amount of emf generated depends on 3 factors
- Magnetic flux density
- Conductor length within the magnetic field
- Rate of speed and the angle at which the conductor cuts the magnetic lines of flux
If a conductor moves parallel to the magnetic lines of flux, no lines of flux are cut; therefore, an emf is not generated
T or F
True
A generator that produces AC is known as
Alternator
One full revolution (360 mechanical degrees) of a 4 pole machine produces
720 electrical degrees, as one cycle is 360 electrical degrees
2 cycles per revolution x 30 revolutions per second =
60 cycles per second / 60 Hz
The output frequency of an AC generator or alternator is determined by 2 factors:
- the number of poles
- the revolutions per minute of the driven shaft
What is equal to the number of completed cycles per revolution, multiplied by the revolutions per second
Frequency in hertz
Frequency in hertz =
(number of motor poles x revolution per minute) / 120
f = (p x rpm) / 120
RPM formula
rpm = (120 x Frequency(Hz)) / number of motor poles
rpm = (120 x f) / p
The value of the emf that an alternator produces rises to a peak, falls to zero, reverses polarity, rises to a peak in the opposite direction and falls to zero is what?
Sine Wave Values
One alternation occurs within _____ degrees of an electrical sine wave
180
Instantaneous value
e = Emax x sine of the angle
Effective value
aka Root Mean Square (RMS)
To calculate the maximum value of a sine wave, divide the rms value by the sine of 45 degrees or multiply the rms by “root 2”
Emax = RMS / 0.707
If the maximum value is given and you want to find the effective value(RMS), transpose the equation as follows
RMS = Emax x 0.707
Unless otherwise indicated, an AC meter reads effective values
T or F
True
root 2 =
1.414 = 1/707
3 factors contribute to impedance in an AC circuit:
- Resistance
- Inductive reactance
- Capacitive reactance
In any circuit, _____ affects the flow of current
Resistance
The property of a circuit that opposes any change of current in the circuit
Inductance
_____ cannot prevent the current from rising or falling, but it does oppose any rise or fall
Inductance
The value of electrical energy established between an area of negative electrical charge and an area of positive electrical charge
Capacitance
A poor electrical conductor acting as an insulator, but easily able to polarize, or separate, positive and negative charges
Dielectric
An electrical component made from 2 plates of a conducting material separated by a dielectric
Capacitor
When a capacitor is connected to an AC supply, it constantly charges and discharges
T or F
True
The property of capacitance affects the circuit by opposing a change in voltage
T or F
True
An opposition to current flow in an AC circuit is
Impedance
- Resistance in a circuit
- Inductance in a circuit opposes
- Capacitance in a circuit opposes
- limits the amount of current
- a change in current
- a change in voltage
- Resistance
- Inductive Reactance
- Capacitive Reactance
- Circuit Impedance
- R (ohms)
- XL (ohms)
- XC (ohms)
- Z (ohms)
Any combination of values of resistance, inductive reactance and capacitive reactance is
Circuit Impedance (Z)
ELI the ICE man
E = volts
I = amps
ELI: Inductance -> voltage leads current
ICE: Capacitance -> current leads voltage
Ohm’s Law in an AC circuit
E = I x Z
Z is the total opposition to current in the ac circuit
