fundamentals of electricity A.C.

generation of sin-waves

created through the principle of electo magnetic induction

inductance in a.c.

-in a.c. inductance occurs continually. -since change in current is constantly occurring, and the changes in flux is always opposing this change in current, an inductor causes current to lag voltage. - this continual opposition to change in current flow will in turn produce an actual opposition to current flow. -the actual opposition to current flow produced by inducatnace in an a.c. circuit is know as inductive reactance(Xl) and is measured in ohms formula: (see picture)

increasing potential

-increasing the strength of the flux field being cut (increasing the current flow through the electromagnet -increasing the density of the lines of flux) -increasing the rate at which the lines of flux are cut ( increasing the speed of the conductor, increasing the number of conductors cutting the flux(wrap in coil)

advantages/disadvantages of A.C.

-much easier to generate large quantities -much easier to change values with out substantial power loss -much easier to transfer over long distances -not as efficient as D.C.

factors which will increase inductance in an inductor

-number of wraps in the coil -length of the coil -width of the coil -type of core.

inductance

-the property of an electric conductor or circuit that causes an electromotive force to be generated by a change in the current flowing. -as current flows in a conductor, a magnetic field forms around the conductor -as current increases, the magnetic field increases -if current flow reverses, the flux field also reverses -the continual changing and reversal of current in a a.c. circuit induces a counter voltage or counter EMF which opposes any change in the initial current flow.

power factor

-the ratio of true power to apparent power -power factor is given by Cos(0) where (0) is the number of degrees of phase change.

inductance in d.c.

1.inductance in d.c. will only occur three times: -when the circuit is first closed -when the circuit is first opened -the instant current changes. 2. the only purpose of inductance in d.c. is to control the amount of time it takes for total current to flow when the circuit is first closed, or stop when the circuit The only purpose of inductanc ein d.c. is to control the amount of time it takes for total current to flow when the circuit is first closed, or stop when the circuit it first opened. -the time is given by time constant -one time constant is defined as the amount of time it takes, in seconds, for 63.2% of total current to begin flow in a circuit it takes five times the constants for total current to fow in a circuit -one time constant formula: TC(lr)=L/R L-total inducatacne in henries R- total resistance in ohms.

power factor

PF=Pt/Pa =cos(theta) =R/Z or Er/Et (series) and= Ir/It (parallel) PF-power factor Pt-true power, in watts Pa-apparent power, in volt-amps Theta- phase shift in degrees R-total resistance, in ohms Z-impedance in ohms Er- voltage drop across "R", volts Et- total voltage (rise), in volts Ir- current through "R", in amps It- total current, in amps

transistors

a device which will allow current flow on only one direction, but the amount of current can be varied by the voltage at the base. -can be used to control a current flow, or can also be used to "amplify: a weak signal (the base) -comes in two forms -Pnb and npn -there is no difference in the operation of the two forms except the polarity of the signal at the base that must be applied to make it function.

three phase electricity

a form of alterating current which has three separate current (and voltage) "sine waves" -capable of producing more power ( higher effective value) -instead of having just one rotating winding ( conductor) there are three, -each winding will produce its own sine wave of voltage(and current). -each winding is 120 degrees apart. -each sine wave is 120 degrees apart, based on conductor rotation.

alternating current

a form of current electricity where the polarity of the source periodically changes.

diodes

allow current flow in one direction, but not the other

sine-wave

alternating current, polarity changes, value changes based on sine function.

triangle-tooth wave

alternating current, polarity periodically changes, value with strait line variation

in-phase

an immediate increase in one (current or voltage) coincides with an immediate increase in the other.

capacitive

any a.c. circuit where Xc is greater then Xl -in a capacitve circuit, current always leads voltage. -purely capacitive is Xc is greater then Xl and Rt=0

resistive

any a.c. circuit where Xc=Xl -in a resistive circuit, there is no phase shift; therefore, PF=1 so true power is equal to apparent power. (most efficient circuit)

inductive

any circuit where Xl is greater then Xc -in a inductive circuit current always lags voltage. -purly inductive Xl is greater then Xc and Rt = 0 (least efficient circuit)

out-of-phase

any condition other than in-phase

period and frequency

are numerical inverses of each other.

polarity of potential

based on two things -orientation of the lines of flux -the direction the conductor is cutting the lines of flux. -determined by the left hand rule(FOR GENERATORS), point first finger in the direction of lines of flux, point thumb in direction of conductor movement, middle finger will point in the direction of current flow.

zener diodes

device that will allow flow in one direction. in the opposite direction, it will allow current flow above a given voltage ( known as zener voltage) -once the zener voltage is exceeded, reverse current flow is allowed with a known(and set) voltage drop across the zener diode. -this characteristic makes zener diodes very useful i voltage regulators.

D.C. to A.C.

done through a device known as a inverter. -the simplest inverter uses a switching mechanism which gives square wave. more advanced inverters control voltage and control voltage and current to give us saw-tooth wave a.c.

a.c. to d.c.

done through a device known as rectifier -simplest form of a rectifier is a single diode -a full-wave rectifier uses multiple diodes to actually reverse the negative alternation -alternators use three-phase, waves, solid state rectifiers

what is inductance (L) measured in?

henries

opposition a.c. and d.c.

in d.c. the only opposition to current flow us resistance. -in a.c. inductive reluctance, capacities reluctance, as well as resistance must be considered.

true power

is power with a result in phase shift included

total opposition in a.c.

known as impedance(Z) measured in ohms in series Z= square root of R^2+X^2 R-total resistance x-total reactants z= impedance in parallel

cycle

one complete sequence of events (of either current or voltage) from zero, to the positive peak, to zero, to the negative peak, and back to zero.

alternation

one half of a cycle, either in the positive or negative direction.

inductive reactants

opposition to change

inductance

opposition to change in current

capacitive reactants

opposition to current flow resulting from capacitance

square waves alternating current

polarity periodically changes but value does not

apparent power

power if it was D.c. or in Phase.

power factor

relation between true power and apparent power

total inductance in a circuit

series- the sum of the individual inductors parallel- the inverse sum of the inverse.

delta to wye /wye to delta

step up transformer ratio 1.73 wye to delta step down ratio 1.73

lead or lag

tell which changes first(given with respect or current) current leads or lags voltage.

capacitance

the ability to store energy in a electro static feild

phase shift

the amount current and voltage are out of phase, in degrees of conductor rotation.

true power

the amount of actual power dissipated in an a.c. circuit -the amount of true power is determined by amount of phase shift -true power is an actual power ut is measured in watts

effective value

the amount of d.c. that is capable of dissipating the same amount of heat as a given sine-wave a.c. (.707 times peak value) (also know as root mean square, or rms -this is what is read off a multi meter -it is how we compare a.c to d.c. -it is what we take our "source voltage

apparent power

the amount of power that would be dissipated in a d.c. circuit -given by the formula P=ie -apparent power is not an actual power, it is measure in volts-amps

average value

the average value of all instantaneous values of one alternation.

resonance

the condition in an a.c. where Xc=Xl. frequency of resonance Fr= (1)/2pie X square root of LxC Fr-frequency resonance, in hertz L- total inductance in henries C- total capacitance, in farads.

electro magnetic induction

the creation of an electrical potential in conduction by passing that conductor through lines of magnetic flux

ohms law in A.C.

the current that flows in a circuit is directly proportional to the voltage of the circuit, and indirectly proportional to the opposition of the circuit

impedance

the effective resistance of an electric circuit or component to alternating current, arising from the combined effects of ohmic resistance and reactance.

peak to peak value

the maximum difference between the positive peak and the negative peak value.

peak value

the maximum instantaneous measure of either current, or voltage, in either the positive or negative direction.

frequency

the number of cycles per second, measured in hertz. F=(# of poles/2)X(Rpm/60)

phase

the positional relationship between current and voltage, with respect to when each is increasing an decreasing.

period

the time required for one cycle to occur, measured in seconds

lenz law

the voltage that is induced into a conductor by change in the flux field caused by a change in the current, is of such a polarity that it opposes the change in the current which caused the change in the flux.

transformer

used to change values of current and voltage. -transformers use the principle of mutual inductance -two forms: step-up and step-down form determined by ratio of primary windings to the secondary windings