Fundamentals of AC #1
How many alternations are in ONE cycle of an AC voltage waveform?
2
The maximum value of a sine wave occurs at which 2 angles?
90 and 270 degrees
What is the insulating material between the plates of a capacitor called?
Dieletric
How many time constants does it take for an inductor to reach maximum steady state value of current?
5
By what percentage does capacitor voltage increase every time constant when a constant voltage is applied to it?
63.2%
A generator that produces AC is called what?
An alternator
If a 16-pole alternator is rotated at 1500 rpm, what is the output frequency?
f = (nxp)/120 = (16x1500)/120 = 200 Hz
What do you need to be aware of when connecting polarized capacitors?
Polarity - connecting them backwards can cause them to explode
What is the formula to calculate a time constant for an inductor?
T = L/R
What is the formula to calculate a time constant for an capacitor?
T = RC
When a 20-pole alternator has made 1 complete revolution, the voltage sine wave will have gone through how many electrical degrees?
360x10 = 3600 elec degrees
** 360 elec degrees are produced when a conductor passes by 2 opposite poles - page 7 of 030201a module **
How many times is a magnitude of 120V (neg or pos) attained in a sine wave with a 170V peak?
4 times per cycle
Name the 3 factors that affect capacitance
C = (kA)/d
k - dielectric constant of the material that separates the plates
A - area of the plates
d - distance between the plates
What device can be connected in an inductive circuit to mitigate damage due to voltage spikes when the circuit is opened?
Discharge resistor
What is the phase relationship between I and V in a capacitor?
I LEADS V by 90 degrees
What is the formula for finding the instantaneous value of voltage on an AC sine wave?
Emax x sin theta
When the effective value of a current waveform is known, which formula must be used to find the peak value?
Ipeak = Ieff x 1.414
When the armature of a coil pulls in, does the inductance decrease or increase?
Increase
The flux path (l) is shorter.
What is the phase relationship between I and V in an inductor?
I LAGS V by 90 degrees
What do the open and closed arrowheads represent in a phasor diagram?
Closed - current
Open - voltage
An AC meter reads 75A. The peak value of current is
75x1.414 = 106.05A
If the max value of an AC waveform is 350V, what is the instantaneous value at 75 degrees?
Name the 4 factors that affect the inductance of a coil
L = (N^2)(mu)(A)/l
N - number of turns of conductor in the coil
mu - permeability of the core material
A - cross sectional area of the core
l - length of the core's magnetic path
What is the inductive reactance of a 450mH coil if it is connected to a 100Hz supply?
2(pi)(f)(L) = 2(3.14)(100)(0.45) = 282.74 ohms
What value of capacitor has a capacitive reactance of 10 ohms when connected to a 60Hz supply?
C = 1/[2(pi)(f)(Xc)] = 1/[2(3.14)(60)(10)]
= 0.000265F OR 265 uF