EC2

In-phase Sine Waves Summation

When two or more sinusoidal waves are in-phase and have the same frequency they may be added (arithmetically) to yield a sine wave of the same frequency. A=A1+A2...An

Out-of-phase Sine Waves Summation

When two or more sinusoidal waves are out-of-phase and have the same frequency they may be added (geometrically) to yield a sine wave of the same frequency. A=√(Ahorizontal)^2+(Avertical)^2

The L-circuit

he current will lag behind the voltage by 90 elec. deg. (ideal). i=Em/wL sin(wt-90)

The sine wave

In general, assuming uniform flux-density distribution between north and south poles, the generated voltage in a coil will be: e=Em sin(a)

The advantage of AC circuits

It can be accomplished economically in large power plants that may be located where fuel and water are abundant.

Form Factor

It is the ratio of the effective value to the average value of the waveform, and is used in computing for correction factors for instrument readings. f.f=Irms/Iave =1.11

Frequency

One cycle is developed for one pair of poles, then, for a multipolar alternator, it will have a frequency of: f=pxrpm/120

Average Value

Since the current is not constant, the average current is the total charge transferred in one period divided by the time of one period. Iave=2/pi x Im

The C-Circuit

The current will lead ahead the voltage by 90 elec. deg. (ideal). i=wCEm sin(wt+90)

Inductance

The property of any electric circuit that opposes the change in current. el=L di/dt

Capacitance

The property which permits it (two plates separated by insulating medium) to accumulate and store electric charge. ec=∫idt/C

Out-of-phase

The voltage and current do not cross zero, or reach their peaks and valleys at the same time.

The R-Circuit

The voltage and current waves are in phase with each other,that is, both are zero simultaneously and increasing in the same direction. i=Em/R sin(wt)

In-phase

The voltage and the current are said to be ________ since their zero, peak, and valley points occur at the same time.

Lag and Lead

These designations are based on the fact that, starting from 0°, the maximum value of the leading phasor (V) occurs ahead of the lagging phasor (I).

Phasors

A term that applies to lines that are given direction with respect to a reference when they are used to replace sinusoidal functions.

Faraday's Law

According to this law, the magnitude of the induced emf by changing the flux through the coil is: e=dΦ/dt x 10^-8

Root-Mean-Square Value

An effective or a-c ampere is defined as the current which, passing through a resistance of given ohmic value, produces heat at the same rate as a dc ampere. Irms=Im/√2

Lead

the current is advanced in phase with respect to the voltage

Lag

the current lags behind the voltage.