Alternating Current Flashcards
As the loop approaches 90 degrees of rotation the flux lines are cut at a ___ rate (more voltage, voltage peak)
faster
Induced voltage at 45 degree angle is ___
70.7 volts
RMS = actual ___ value
AC
Skin effect in AC circuits
frequency goes ___, skin effect goes ___
Large CMA, Resistance goes ___
up, up
down
Skin effect = ___
tendency of electrons to move towards outside of conductor
phase = current rise and falls at the ___ rate as voltage, and reverses in polarity the ___ as well. (reverse flow)
same
resistive loads - contain pure ____
-produce heat
-current and voltage are in ___ with each other
resistance, phase
___ circuit - electrons travel through entire conductor
___ circuit - electrons forced outside conductor (skin effect)
DC, AC
ripple - pulsating DC - turns on and off but never changes ___
polarity
Inductive capacitance - ___
Impedance - ___
Inductive reactance (__)
(inductance H or L) (reactance X)
farads, ohms, XL
XL (inductive reactance) = ___
2 pie f length
Each is 63.5 (5 of them)
100 - 63.5 = 36.8
Inductance in AC circuits
____ = AC load, usually with coil
- motors, transformers, lightning ballast, and chokes
Inductance (L)
Impedance rules: (4 of them)
1) cutting of magnetic flux through coil, induce voltage
2) Induced voltage ___ in polarity to applied voltage (CEMF) (Counter Electromotive Force)
3) # amount of induced voltage proportional to ___ of current change
4) An inductor opposes a change of ___
opposite, rate, current
Voltage goes up, current change goes up
True or False
True
An inductor opposes a change of current
True or False
True
Inductors connected to AC voltage
-induced voltage is ___ degrees out of phase with applied voltage and opposition to applied voltage
currents flow (out)
decrease (collapse)
180
E (INST) = the voltage at any point on the wave form
___ = impedance (ohms) (h = z)
___ = Reactance in ohms (y = o)
___ = Resistance in ohms (x = a)
Z ,X, R
___ = Apparent power (VA) (h=z)
___ = Reactive power (VARS) (y = o)
___ = True power (Watts) (x = a)
VA, VARS, Watts
____ = AVR (E, I)
____ Effective (E, I)
____ (Pav, P)
Instantaneous (lower case) = sin (theta)
AVR = 0.637
Effective (RMS) = 0.707 (E, I)
Effective (RMS) = 0.5 (P)
Em = Blv
Im = EM/R
Pm = Em x Im
0.637, 0.707,, 0.5
Capital (m) = max
Capital = Effective
lower case = instantaneous
AVR = average
AVR (av) = full cycle = 0
Everything basically calculated by peak (Pm = Im x Rm) or
Effective (capital) P = E power of 2 / R
to get resistance (ohms)
60 cycles per 1 sec = 60 Hz
oscilloscope = see ripple voltages add
Magnetic Induction
____ = rate of certain occurences.
current rise 63.2 percent each time constant (5 times constant)
Exponential curve
high permeability (silicon, steel, and soft iron)
low permeability (brass, copper, or aluminium)
Induced voltage spike
voltage spike - current flow stops and decrease.
- suppressed by ___ (MOV)
Diode = permits current flow in only one direction
Metal Oxide Varistor
Inductance in AC circuit
Inductance - creates voltage by change to ____ (reverse polarity) or increase or decrease of ___ in different directions.
& magnitude (direction of armature rotation)
- speed of rotation faster, more induced voltage
magnetic field, current
Lenz’s law - an induced voltage or current opposes the motion that causes it
-___ always oppose a change in current
Inductors
Vertical = 180 degrees and 360 degrees
Flat (parallel) = 270 degrees and 90 degrees
shunt - field pole coil
Magnetic Inductance
Amount of Voltage Induced in a conductor
1) The number of turns of wire
2) The strength of the magnetic field (flux density)
3) The speed of the cutting action
Solenoid = converts energy (____) to ____
uses relay
(electrical), mechanical
Impedance (ohms) =(inductive and capacitance)
Hz = (# poles x RPM) / 120
T (time, secs) = L (Henry, Inductance) / R (resistance)
XL = ___
Inductive reactance, proportional to inductance) = constant x pie x frequency in hertz (Hz) x inductance in henrys (H)
proportional to:
- # of turns of wire
- strength of magnetic field
- the speed of cutting action (relative motion between inductor & magnetic lines of flux)
2 pie f L
Terms (symbol) (unit)
Reactance (X) (ohms)
Inductance (L) H)
capacitance (C) (F)
Inductive reactance (XL) (ohms)
Capacitive reactance (XC) (Farads)
Impedance (Z) (ohms)
E (INST) = voltage at any point on the wave form
Wave forms (3 of them)
(Sine Wave, Square Waves, and Triangle waves)
Oscillators = produce Square waves
___ = a triangle wave
(voltage rise at a constant rate with respect to time)
linear wave
Sine wave - contains 360 degrees
each complete 360 degree is called a cycle
frequency = # number of complete cycles in one second
- measured in hertz (Hz)
the ___ the flux lines are cut at an angle, ___ flux lines cut per second, so less induced voltage as goes from 30 degrees to eventual 90 degrees the max lines cut
more, less
The induced voltage after 90 degrees of rotation is ___
-the voltage after 30 degrees of rotation will be ___ because the sine angle of 30 degree angle is 0.5 (100 x 0.5) = 50 volt
100 v, 50 volts
peak value or ___ - measure from zero to highest value in either positive or negative direction
-the peak value is either positive or negative direction.
(amplitude)
- the peak value is one - half of the peak-to-peak value
True or False
True
___ sine wave value of 100 volt cannot produce as much power as 100 volt of ___. (Since it increase to 100 volt but decrease to zero, equal time)
AC, DC
(actual AC value) RMS = peak x 0.707
peak = RMS x 1.414
(rating) - just use an ___ value of AC voltage that produce same power as of DC volt value
equal
AC (Trigonometry)
Apparent power (VA) - the value found by multiplying the ___ by the ___ of an AC circuit.
-apparent power - measured in volt-ampere (VA) & should not be confused with true power, measured in Watts.
Watt (W) - a measure of true power
applied voltage, total current
Impedance (Z) - ___
the total opposition to current flow in an electrical circuit
Reactance - ____
the opposition to current flow in an AC circuit offered by pure inductance or pure capacitance
Resistance - the opposition to current flow in an AC or DC circuit
Average values - of voltage & current are actually ___ values
- when sine wave of AC is changed into DC with rectifier.
The average value produces the same amount of power as a non pulsating battery - source voltage
(half-wave rectifier) average voltage - Efm x 0.637 = Eav (full-wave) then
divide by 2
Eav / 2 = Eav (half-wave)
DC
Wavelength (λ)(lambda) - ___
distance the radiating field or signal can travel during one cycle.
λ (wavelength) = speed of light (meter per sec) / frequency
300,000,000 m/s / 100,000,000 Hz
DC circuits have only one basic type of load (resistive) - true power
- power in pure resistive AC circuits have watts (power)
Conductor Resistance (ohms) depends on: (3 things)
- type of ___ (conductor is made of)
- ___ (conductor)
- ___ (conductor)
material, length, diameter
eddy currents from AC cause electrons to repel to outer surface of conductor (____)
- ___ diameter, increase resistance
skin effect, decrease
A (quantity) = XL (inductive reactance) / R (resistance)
pure inductance (round wave)
internal resistance (jagged wave)
Watts
P (True power) = ER x IR
AC inductance can only periods when current & voltage are both (+) or (-)
Cannot use P = V drop x I
P = E power of square / R
P = I power of square x R
Total voltage for AC inductance must use vectors
(inductive total voltage) ET = ER (resistive voltage) + EL (inductive voltage)
VARs (reactive power)= ___ power of square (reactive current) x ___ (inductive reactance)
-quadrature power
-Wattless power
IL, XL
VA (apparent power) = ___
ET x IT
Power Factor (PF) = True power (Watts) / apparent power (VA)
PF = R (resistance) / Z (____)
PF = P (Watts) / VA (____)
PF = ER (voltage drop) / ET (____)
- cannot use current because current is the same (series AC, inductive ohms)
impedance, apparent, total voltage
angle theta (θ) = angle of VA (apparent) = VAR (reactive) + Watts (true)
cosθ = ___
To find angle 53 degrees which means current & voltage is 53 degree out of phase with each other.
y = o = VAR (reactive)
x= a = P (Watts)
h = VA (apparent)
PF = Watts / VA
(Total current) IT = VA / ___
(Impedance) Z = ET/ __
(Power Factor) PF = WT / ___
ET, IT, VA
